Allergy symptoms worry more and more people every year. Often the disease is not episodic, but permanent. There are many remedies for getting rid of allergies, but only second and third generation antihistamines have a minimal amount of side effects.
An allergic reaction refers to complex biochemical processes, in which a biologically active substance, histamine, plays an important role. The number of patients forced to resort to the use of antihistamines is increasing every year. The reasons for the increase in the consumption of antihistamines and other antiallergic drugs include the aggravation of the environmental situation in the world, the uncontrolled use of drugs, the daily use of household chemicals with an unexplored effect on the human body.
Allergy sufferers notice a decrease in the potency of drugs that were previously effective. There are also those that fix an undesirable side effect from antiallergic drugs. It was these factors that prompted scientists to find more effective allergy drugs with a minimum number of side effects: second and third generation antihistamines.
How the drugs work
The first antihistamines appeared in the first third of the last century. At that time, they coped with the tasks set, namely: they quickly blocked the effect of histamine on specific H1 - histamine receptors, thereby reducing the severity of allergic reactions ( skin itching, rashes, rhinitis, bronchospasm, anaphylactic shock). These drugs also had a number of disadvantages.
First generation
They acted for a short time, penetrated the blood-brain barrier. Such side effects forced the patient to take the medicine several times a day in sufficiently large doses, and the antihistamine itself caused sedation, drowsiness, and the inability to engage in activities that require a high reaction rate and concentration. It is known about the adverse effect of such drugs on the gastrointestinal tract.
Long-term use of the first generation antihistamine was undesirable. Many representatives of this pharmacological group are contraindicated in children and pregnant women.
Research in the field of studying the increased reaction of the body to a particular substance made it possible to establish the cause of allergies, the mechanism of its development and the main biochemical components that are involved in it. Thus, it was possible to synthesize the second and third generations of antihistamines with somewhat different pharmacological effects.
The undoubted advantages of these drugs include the absence or minimal manifestation of a calming effect, there is no addiction, the simultaneous intake of food does not affect the therapeutic effect of drugs. In addition, these drugs exhibit a high degree of specificity for blocking H1-histamine receptors without affecting other types of receptors. A few hours after taking these drugs, the maximum therapeutic effect occurs.
Second generation
The second generation of antihistamines appeared relatively recently. . Their essential advantage is that they do not penetrate the blood-brain barrier, drowsiness, dizziness and weakness are mild. The mechanism of action of representatives of the second generation of antiallergic drugs is based on a specific blocking effect on H1 receptors.
At the same time, these drugs do not affect other receptors; after their use, tachyphylaxis does not develop (a decrease in the therapeutic effect with repeated use). A single dose of a representative of this group of drugs is enough for the pharmacological effect to last for a day. And after stopping the course of therapy, the effect persists for a week.
Representatives of second-generation antihistamines include Astemizol (Gismanal), Loratadin (Lorano, Claritin, Erolin, Tyrlor, Lomilan), Terfenadine (Teridin, Trexil, Tofrin, Tamagon, Bronal), Acrivastine (Semprex), Azelastine (Allergodil), Ebastin ( Ebastel, Clover, Kestinlio, Kestin), Desloratadine (Eden, Erius).
Desloratadine in the form of a suspension can be prescribed to children from one year old, astemizole and loratadine - from the second year, the rest - from an older age.
third generation
The third generation of antihistamines can be described as prodrugs or intermediates that are converted into an active form in the body and have a therapeutic effect. And only cetirizine was obtained by modifying hydroxyzine, a representative of the first generation of antiallergic drugs. Thanks to these chemical changes, the third generation of antihistamines got rid of unwanted side effects, and the pharmacological effect increased significantly. It is representatives of the third generation that can rightly be considered metabolites of previous generations.
This group of antiallergic drugs includes Fexofenadine (Telfast, Fexofast, Gifast, Allegra) and Cetirizine (Cetrin, Zodak, Zirtek, Zincet). Cetirizine can be used in children from the age of six months, fexofenadine - from the age of six.
Main Side Effects
Compared with the first generation of antihistamines, the second and third generations have fewer side effects. However, there is no need to talk about their maximum safety.
Thus, it has been proven that drugs of the 2nd and 3rd generations of antihistamines can accumulate and not be excreted from the body for a long time. This fact can also be considered as an undesirable effect due to the fact that the simultaneous use of several drugs can negatively affect the internal systems and organs of a person.
It is known that the violation of the liver and kidneys must be taken into account by the doctor to adjust the therapeutic dose. The combined use of antiallergic drugs with ketoconazole or erythromycin increases the manifestation of side effects.
When using almost all antihistamine drugs, an unpleasant sensation of dryness of the mucous membranes, nausea, vomiting, headache, and fatigue may occur.
Second-generation antihistamines may exhibit cardiotoxic effects due to their ability to block potassium channels in the myocardium. In this regard, ECG monitoring should be carried out periodically in order to timely cancel the use of antiallergic drugs. Many doctors avoid prescribing such drugs in people with heart conditions.
Despite the selectivity of the action of modern antihistamines, side effects such as drowsiness, dizziness, impaired concentration, nervousness, distortion of sound perception, visual disturbances are not excluded.
The adverse effect of second and third generation antihistamines on the developing fetus when used in pregnant women has not been fully proven, therefore, under certain circumstances, they can be used to a limited extent under the supervision of a physician. These medicines should not be used by breastfeeding women.
Application area
The most correct solution in the treatment of conditions associated with allergies is the complete exclusion of the patient's contact with a substance that causes unpleasant symptoms in the form of bronchospasm, conjunctivitis, rhinitis, and allergic dermatosis. To do this, conduct a series of studies that determine the allergen - the cause of the disease. It is allergens that cause swelling and spasm of the respiratory tract, skin itching, characteristic rashes, unpleasant symptoms from the gastrointestinal tract in the form of spasms and colic, expansion and increased permeability of capillaries, lowering blood pressure, and heart rhythm disturbance.
Unfortunately, it is impossible to completely eliminate the effect of substances that cause an allergic reaction in most cases. The influence of substances that cause allergic reactions can be both short-term, episodic, and long-term, throughout the season or all year round.
The most acceptable way to cope with allergies today is the use of special medicines that block the effect of the allergen on sensitive receptors. That is why in such situations, antihistamines of the second and third generations are used.
Rhinitis seasonal and throughout the year, allergic dermatoses, an integrated approach to the treatment of bronchial asthma, prevention of spasms of the upper respiratory tract - these are the main areas in which the second and third generations of antiallergic drugs are used. Long-term and continuous use of such anti-allergic groups does not reduce the manifestation of the necessary therapeutic effects, does not aggravate the patient's condition, does not cause a new side effect.
Most antihistamine medicines are categorized as over-the-counter drugs. However, self-medication with the use of such drugs is not justified. Together with the doctor, it is necessary to find out the cause of the increased sensitivity of the body to a particular substance, to determine the main directions of therapeutic measures.
Historically, the term "antihistamines" means drugs that block H1-histamine receptors, and drugs that act on H2-histamine receptors (cimetidine, ranitidine, famotidine, etc.) are called H2-histamine blockers. The former are used to treat allergic diseases, the latter are used as antisecretory agents.
Histamine, this most important mediator of various physiological and pathological processes in the body, was chemically synthesized in 1907. Subsequently, it was isolated from animal and human tissues (Windaus A., Vogt W.). Even later, its functions were determined: gastric secretion, neurotransmitter function in the central nervous system, allergic reactions, inflammation, etc. Almost 20 years later, in 1936, the first substances with antihistamine activity were created (Bovet D., Staub A.). And already in the 60s, the heterogeneity of histamine receptors in the body was proven and three of their subtypes were identified: H1, H2 and H3, differing in structure, localization and physiological effects that occur during their activation and blockade. Since that time, an active period of synthesis and clinical testing of various antihistamines begins.
Numerous studies have shown that histamine, acting on the receptors of the respiratory system, eyes and skin, causes characteristic allergy symptoms, and antihistamines that selectively block H1-type receptors can prevent and stop them.
Most of the antihistamines used have a number of specific pharmacological properties that characterize them as a separate group. These include the following effects: antipruritic, decongestant, antispastic, anticholinergic, antiserotonin, sedative and local anesthetic, as well as the prevention of histamine-induced bronchospasm. Some of them are not due to histamine blockade, but to structural features.
Antihistamines block the action of histamine on H1 receptors by the mechanism of competitive inhibition, and their affinity for these receptors is much lower than that of histamine. Therefore, these drugs are not able to displace histamine bound to the receptor, they only block unoccupied or released receptors. Accordingly, H1 blockers are most effective in preventing immediate allergic reactions, and in the case of a developed reaction, they prevent the release of new portions of histamine.
According to their chemical structure, most of them are fat-soluble amines, which have a similar structure. The core (R1) is represented by an aromatic and/or heterocyclic group and is linked via a nitrogen, oxygen or carbon (X) molecule to the amino group. The core determines the severity of antihistamine activity and some of the properties of the substance. Knowing its composition, one can predict the strength of the drug and its effects, such as the ability to penetrate the blood-brain barrier.
There are several classifications of antihistamines, although none of them is generally accepted. According to one of the most popular classifications, antihistamines are divided into first and second generation drugs according to the time of creation. First-generation drugs are also called sedatives (according to the dominant side effect), in contrast to non-sedative second-generation drugs. At present, it is customary to single out the third generation: it includes fundamentally new drugs - active metabolites that, in addition to the highest antihistamine activity, exhibit the absence of a sedative effect and the cardiotoxic effect characteristic of second-generation drugs (see).
In addition, according to the chemical structure (depending on the X-bond), antihistamines are divided into several groups (ethanolamines, ethylenediamines, alkylamines, derivatives of alphacarboline, quinuclidine, phenothiazine, piperazine and piperidine).
First generation antihistamines (sedatives). All of them are well soluble in fats and, in addition to H1-histamine, also block cholinergic, muscarinic and serotonin receptors. Being competitive blockers, they reversibly bind to H1 receptors, which leads to the use of rather high doses. The following pharmacological properties are most characteristic of them.
- The sedative effect is determined by the fact that most of the first-generation antihistamines, being easily dissolved in lipids, penetrate well through the blood-brain barrier and bind to the H1 receptors of the brain. Perhaps their sedative effect consists of blocking the central serotonin and acetylcholine receptors. The degree of manifestation of the sedative effect of the first generation varies in different drugs and in different patients from moderate to severe and increases when combined with alcohol and psychotropic drugs. Some of them are used as sleeping pills (doxylamine). Rarely, instead of sedation, psychomotor agitation occurs (more often in medium therapeutic doses in children and in high toxic doses in adults). Due to the sedative effect, most drugs should not be used during tasks that require attention. All first-generation drugs potentiate the action of sedative and hypnotic drugs, narcotic and non-narcotic analgesics, monoamine oxidase inhibitors and alcohol.
- The anxiolytic effect characteristic of hydroxyzine may be due to the suppression of activity in certain areas of the subcortical region of the central nervous system.
- Atropine-like reactions associated with the anticholinergic properties of drugs are most characteristic of ethanolamines and ethylenediamines. Manifested by dry mouth and nasopharynx, urinary retention, constipation, tachycardia and visual impairment. These properties ensure the effectiveness of the discussed remedies in non-allergic rhinitis. At the same time, they can increase obstruction in bronchial asthma (due to an increase in sputum viscosity), exacerbate glaucoma and lead to infravesical obstruction in prostate adenoma, etc.
- The antiemetic and antiswaying effects are also probably associated with the central anticholinergic effect of the drugs. Some antihistamines (diphenhydramine, promethazine, cyclizine, meclizine) reduce the stimulation of vestibular receptors and inhibit the function of the labyrinth, and therefore can be used for motion sickness.
- A number of H1-histamine blockers reduce the symptoms of parkinsonism, which is due to central inhibition of the effects of acetylcholine.
- Antitussive action is most characteristic of diphenhydramine, it is realized through a direct action on the cough center in the medulla oblongata.
- The antiserotonin effect, which is primarily characteristic of cyproheptadine, determines its use in migraine.
- The α1-blocking effect with peripheral vasodilation, especially seen with phenothiazine antihistamines, may lead to a transient decrease in blood pressure in sensitive individuals.
- Local anesthetic (cocaine-like) action is characteristic of most antihistamines (occurs due to a decrease in membrane permeability to sodium ions). Diphenhydramine and promethazine are stronger local anesthetics than novocaine. However, they have systemic quinidine-like effects, manifested by prolongation of the refractory phase and the development of ventricular tachycardia.
- Tachyphylaxis: decrease in antihistamine activity with long-term use, confirming the need for alternating drugs every 2-3 weeks.
- It should be noted that the first generation antihistamines differ from the second generation in the short duration of exposure with a relatively rapid onset of the clinical effect. Many of them are available in parenteral forms. All of the above, as well as low cost, determine the widespread use of antihistamines today.
Moreover, many of the qualities that were discussed allowed the “old” antihistamines to occupy their niche in the treatment of certain pathologies (migraine, sleep disorders, extrapyramidal disorders, anxiety, motion sickness, etc.) that are not associated with allergies. Many first-generation antihistamines are included in combination preparations used for colds, as sedatives, hypnotics, and other components.
The most commonly used are chloropyramine, diphenhydramine, clemastine, cyproheptadine, promethazine, phencarol, and hydroxyzine.
Chloropyramine(Suprastin) is one of the most widely used sedative antihistamines. It has significant antihistamine activity, peripheral anticholinergic and moderate antispasmodic action. Effective in most cases for the treatment of seasonal and year-round allergic rhinoconjunctivitis, angioedema, urticaria, atopic dermatitis, eczema, itching of various etiologies; in parenteral form - for the treatment of acute allergic conditions requiring emergency care. Provides a wide range of usable therapeutic doses. It does not accumulate in the blood serum, so it does not cause an overdose with prolonged use. Suprastin is characterized by a rapid onset of effect and short duration (including side effects). At the same time, chloropyramine can be combined with non-sedating H1-blockers in order to increase the duration of the antiallergic effect. Suprastin is currently one of the best-selling antihistamines in Russia. This is objectively related to the proven high efficiency, controllability of its clinical effect, the availability of various dosage forms, including injections, and low cost.
Diphenhydramine, best known in our country under the name diphenhydramine, is one of the first synthesized H1-blockers. It has a fairly high antihistamine activity and reduces the severity of allergic and pseudo-allergic reactions. Due to the significant anticholinergic effect, it has an antitussive, antiemetic effect and at the same time causes dry mucous membranes, urinary retention. Due to lipophilicity, diphenhydramine gives pronounced sedation and can be used as a hypnotic. It has a significant local anesthetic effect, as a result of which it is sometimes used as an alternative for intolerance to novocaine and lidocaine. Diphenhydramine is presented in various dosage forms, including for parenteral use, which determined its widespread use in emergency therapy. However, a significant range of side effects, unpredictability of consequences and effects on the central nervous system require increased attention in its application and, if possible, the use of alternative means.
clemastine(tavegil) is a highly effective antihistamine drug similar in action to diphenhydramine. It has a high anticholinergic activity, but to a lesser extent penetrates the blood-brain barrier. It also exists in an injectable form, which can be used as an additional remedy for anaphylactic shock and angioedema, for the prevention and treatment of allergic and pseudo-allergic reactions. However, hypersensitivity to clemastine and other antihistamines with a similar chemical structure is known.
Cyproheptadine(peritol), along with antihistamine, has a significant antiserotonin effect. In this regard, it is mainly used in some forms of migraine, dumping syndrome, as an appetite enhancer, in anorexia of various origins. It is the drug of choice for cold urticaria.
Promethazine(pipolfen) - a pronounced effect on the central nervous system determined its use in Meniere's syndrome, chorea, encephalitis, sea and air sickness, as an antiemetic. In anesthesiology, promethazine is used as a component of lytic mixtures to potentiate anesthesia.
Quifenadine(fenkarol) - has less antihistamine activity than diphenhydramine, but is also characterized by less penetration through the blood-brain barrier, which determines the lower severity of its sedative properties. In addition, fenkarol not only blocks histamine H1 receptors, but also reduces the content of histamine in tissues. May be used in the development of tolerance to other sedative antihistamines.
Hydroxyzine(atarax) - despite the existing antihistamine activity, it is not used as an antiallergic agent. It is used as an anxiolytic, sedative, muscle relaxant and antipruritic agent.
Thus, first-generation antihistamines that affect both H1- and other receptors (serotonin, central and peripheral cholinergic receptors, a-adrenergic receptors) have different effects, which determined their use in a variety of conditions. But the severity of side effects does not allow us to consider them as drugs of first choice in the treatment of allergic diseases. The experience gained with their use has allowed the development of unidirectional drugs - the second generation of antihistamines.
Second generation antihistamines (non-sedating). Unlike the previous generation, they have almost no sedative and anticholinergic effects, but differ in their selective action on H1 receptors. However, for them, a cardiotoxic effect was noted to varying degrees.
The following properties are the most common for them.
- High specificity and high affinity for H1 receptors with no effect on choline and serotonin receptors.
- Rapid onset of clinical effect and duration of action. Prolongation can be achieved due to high protein binding, accumulation of the drug and its metabolites in the body, and delayed elimination.
- Minimal sedative effect when using drugs in therapeutic doses. It is explained by the weak passage of the blood-brain barrier due to the peculiarities of the structure of these funds. Some particularly sensitive individuals may experience moderate drowsiness, which is rarely the reason for discontinuing the drug.
- Absence of tachyphylaxis with prolonged use.
- The ability to block the potassium channels of the heart muscle, which is associated with prolongation of the QT interval and cardiac arrhythmia. The risk of this side effect increases when antihistamines are combined with antifungals (ketoconazole and itraconazole), macrolides (erythromycin and clarithromycin), antidepressants (fluoxetine, sertraline and paroxetine), grapefruit juice, and in patients with severe liver dysfunction.
- Absence of parenteral formulations, however, some of them (azelastine, levocabastine, bamipine) are available as topical formulations.
Below are second-generation antihistamines with their most characteristic properties.
Terfenadine- the first antihistamine drug, devoid of a depressant effect on the central nervous system. Its creation in 1977 was the result of a study of both the types of histamine receptors and the features of the structure and action of existing H1-blockers, and laid the foundation for the development of a new generation of antihistamines. Currently, terfenadine is used less and less, which is associated with its increased ability to cause fatal arrhythmias associated with prolongation of the QT interval (torsade de pointes).
Astemizol- one of the longest acting drugs of the group (the half-life of its active metabolite is up to 20 days). It is characterized by irreversible binding to H1 receptors. Virtually no sedative effect, does not interact with alcohol. Since astemizole has a delayed effect on the course of the disease, it is not advisable to use it in an acute process, but it may be justified in chronic allergic diseases. Since the drug has the ability to accumulate in the body, the risk of developing serious heart rhythm disturbances, sometimes fatal, increases. Due to these dangerous side effects, the sale of astemizole in the United States and some other countries has been suspended.
Akrivastine(semprex) is a drug with high antihistamine activity with a minimally pronounced sedative and anticholinergic effect. A feature of its pharmacokinetics is a low level of metabolism and the absence of cumulation. Acrivastine is preferred in cases where there is no need for permanent antiallergic treatment due to the rapid onset of effect and short-term effect, which allows for a flexible dosing regimen.
Dimethenden(Fenistil) - is closest to the first generation antihistamines, but differs from them in a much less pronounced sedative and muscarinic effect, higher antiallergic activity and duration of action.
Loratadine(claritin) is one of the most purchased drugs of the second generation, which is quite understandable and logical. Its antihistamine activity is higher than that of astemizole and terfenadine, due to the greater strength of binding to peripheral H1 receptors. The drug is devoid of a sedative effect and does not potentiate the effect of alcohol. In addition, loratadine practically does not interact with other drugs and does not have a cardiotoxic effect.
The following antihistamines are topical preparations and are intended to relieve local manifestations of allergies.
Levocabastin(Histimet) is used as an eye drop for the treatment of histamine-dependent allergic conjunctivitis or as a spray for allergic rhinitis. When applied topically, it enters the systemic circulation in a small amount and does not have undesirable effects on the central nervous and cardiovascular systems.
Azelastine(allergodil) is a highly effective remedy for the treatment of allergic rhinitis and conjunctivitis. Used as a nasal spray and eye drops, azelastine has little to no systemic effects.
Another topical antihistamine, bamipine (soventol), in the form of a gel, is intended for use in allergic skin lesions accompanied by itching, insect bites, jellyfish burns, frostbite, sunburn, and mild thermal burns.
Antihistamines of the third generation (metabolites). Their fundamental difference is that they are active metabolites of antihistamines of the previous generation. Their main feature is the inability to influence the QT interval. Currently, there are two drugs - cetirizine and fexofenadine.
cetirizine(Zyrtec) is a highly selective peripheral H1 receptor antagonist. It is an active metabolite of hydroxyzine, which has a much less pronounced sedative effect. Cetirizine is almost not metabolized in the body, and the rate of its excretion depends on the function of the kidneys. Its characteristic feature is its high ability to penetrate the skin and, accordingly, its effectiveness in skin manifestations of allergies. Cetirizine neither experimentally nor in the clinic showed any arrhythmogenic effect on the heart, which predetermined the area of practical use of metabolite drugs and determined the creation of a new drug, fexofenadine.
Fexofenadine(telfast) is the active metabolite of terfenadine. Fexofenadine does not undergo transformations in the body and its kinetics does not change with impaired liver and kidney function. It does not enter into any drug interactions, does not have a sedative effect and does not affect psychomotor activity. In this regard, the drug is approved for use by persons whose activities require increased attention. A study of the effect of fexofenadine on the QT value showed, both in the experiment and in the clinic, the complete absence of a cardiotropic effect when using high doses and with long-term use. Along with maximum safety, this remedy demonstrates the ability to stop symptoms in the treatment of seasonal allergic rhinitis and chronic idiopathic urticaria. Thus, the pharmacokinetics, safety profile and high clinical efficacy make fexofenadine the most promising of the antihistamines at present.
So, in the doctor's arsenal there is a sufficient amount of antihistamines with different properties. It must be remembered that they provide only symptomatic relief from allergies. In addition, depending on the specific situation, you can use both different drugs and their diverse forms. It is also important for the physician to be aware of the safety of antihistamines.
| 1st generation | II generation | III generation |
|
|
|
There are several groups of drugs used in allergic diseases. It:
- antihistamines;
- membrane stabilizing drugs - preparations of cromoglycic acid () and ketotifen;
- topical and systemic glucocorticosteroids;
- intranasal decongestants.
In this article, we will only talk about the first group - antihistamines. These are drugs that block H1-histamine receptors and, as a result, reduce the severity of allergic reactions. To date, there are more than 60 antihistamines for systemic use. Depending on the chemical structure and the effects on the human body, these drugs are combined into groups, which we will discuss below.
What is histamine and histamine receptors, the principle of action of antihistamines
There are several types of histamine receptors in the human body.Histamine is a biogenic compound formed as a result of a number of biochemical processes, and is one of the mediators involved in the regulation of vital body functions and playing a leading role in the development of many diseases.
Under normal conditions, this substance is in the body in an inactive, bound state, however, with various pathological processes (hay fever, and so on), the amount of free histamine increases many times, which is manifested by a number of specific and nonspecific symptoms.
Free histamine has the following effects on the human body:
- causes spasm of smooth muscles (including the muscles of the bronchi);
- dilates capillaries and lowers blood pressure;
- causes stagnation of blood in the capillaries and an increase in the permeability of their walls, which entails thickening of the blood and swelling of the tissues surrounding the affected vessel;
- reflexively excites the cells of the adrenal medulla - as a result, adrenaline is released, which contributes to the narrowing of arterioles and an increase in heart rate;
- enhances the secretion of gastric juice;
- plays the role of a neurotransmitter in the central nervous system.
Externally, these effects are manifested as follows:
- bronchospasm occurs;
- the nasal mucosa swells - nasal congestion appears and mucus is released from it;
- itching, redness of the skin appears, all kinds of elements of a rash form on it - from spots to blisters;
- the digestive tract responds to an increase in the level of histamine in the blood with a spasm of the smooth muscles of the organs - there are pronounced cramping pains throughout the abdomen, as well as an increase in the secretion of digestive enzymes;
- from the side of the cardiovascular system, and can be noted.
In the body, there are special receptors for which histamine has an affinity - H1, H2 and H3-histamine receptors. In the development of allergic reactions, mainly H1-histamine receptors play a role, located in the smooth muscles of the internal organs, in particular, the bronchi, in the inner membrane - the endothelium - of the vessels, in the skin, and also in the central nervous system.
Antihistamines affect precisely this group of receptors, blocking the action of histamine by the type of competitive inhibition. That is, the drug does not displace histamine already bound to the receptor, but occupies a free receptor, preventing histamine from attaching to it.
If all receptors are occupied, the body recognizes this and gives a signal to reduce the production of histamine. Thus, antihistamines prevent the release of new portions of histamine, and are also means of preventing the occurrence of allergic reactions.
Classification of antihistamines
Several classifications of drugs in this group have been developed, but none of them is generally accepted.
Depending on the characteristics of the chemical structure, antihistamines are divided into the following groups:
- ethylenediamines;
- ethanolamines;
- alkylamines;
- quinuclidine derivatives;
- alphacarboline derivatives;
- phenothiazine derivatives;
- piperidine derivatives;
- piperazine derivatives.
In clinical practice, the classification of antihistamines by generations has become more widely used, which are currently distinguished by 3:
- 1st generation antihistamines:
- diphenhydramine (diphenhydramine);
- doxylamine (donormil);
- clemastine (tavegil);
- chloropyramine (suprastin);
- mebhydrolin (diazolin);
- promethazine (pipolphen);
- quifenadine (fencarol);
- cyproheptadine (peritol) and others.
- 2nd generation antihistamines:
- acrivastine (semprex);
- dimethindene (fenistil);
- terfenadine (histadine);
- azelastine (allergodil);
- loratadine (lorano);
- cetirizine (cetrin);
- bamipin (soventol).
- 3rd generation antihistamines:
- fexofenadine (telfast);
- deslorathodine (erius);
- levocetirizine.
1st generation antihistamines
Antihistamines of the first generation have a pronounced sedative effect. According to the predominant side effect, drugs in this group are also called sedatives. They interact not only with histamine receptors, but also with a number of other receptors, which determines their individual effects. They act for a short time, which is why they require multiple doses during the day. The effect comes quickly. Available in different dosage forms - for oral administration (in the form of tablets, drops) and parenteral administration (in the form of a solution for injection). Affordable.
With prolonged use of these drugs, their antihistamine effectiveness is significantly reduced, which necessitates a periodic change of the drug - once every 2-3 weeks.
Some 1st generation antihistamines are included in combination medicines for the treatment of colds, as well as sleeping pills and sedatives.
The main effects of 1st generation antihistamines are:
- local anesthetic - associated with a decrease in membrane permeability to sodium; the most powerful local anesthetics from the drugs of this group are promethazine and diphenhydramine;
- sedative - due to a high degree of penetration of drugs of this group through the blood-brain barrier (that is, into the brain); the degree of severity of this effect in different drugs is different, it is most pronounced in doxylamine (it is often used as a sleeping pill); the sedative effect is enhanced with the simultaneous use of alcoholic beverages or the use of psychotropic drugs; when taking extremely high doses of the drug, instead of the effect of sedation, marked excitement is noted;
- anti-anxiety, calming effect is also associated with the penetration of the active substance into the central nervous system; maximally expressed in hydroxyzine;
- anti-sickness and antiemetic - some representatives of the drugs in this group inhibit the function of the labyrinth of the inner ear and reduce the stimulation of receptors of the vestibular apparatus - they are sometimes used for Meniere's disease and motion sickness in transport; this effect is most pronounced in drugs such as diphenhydramine, promethazine;
- atropine-like action - cause dryness of the mucous membranes of the oral and nasal cavities, increased heart rate, visual disturbances, urinary retention, constipation; may exacerbate bronchial obstruction, lead to exacerbation of glaucoma and obstruction in - with these diseases are not used; these effects are most pronounced in ethylenediamines and ethanolamines;
- antitussive - drugs of this group, in particular, diphenhydramine, have an effect directly on the cough center located in the medulla oblongata;
- the antiparkinsonian effect is obtained by inhibiting the effects of acetylcholine by the antihistamine;
- antiserotonin effect - the drug binds to serotonin receptors, alleviating the condition of patients suffering from migraine; especially pronounced in cyproheptadine;
- expansion of peripheral vessels - leads to a decrease in blood pressure; maximally expressed in phenothiazine preparations.
Since drugs in this group have a number of undesirable effects, they are not the drugs of choice for the treatment of allergies, but they are still often used for it.
Below are the individual, most commonly used, representatives of the drugs in this group.
diphenhydramine (diphenhydramine)
One of the first antihistamines. It has a pronounced antihistamine activity, in addition, it has a local anesthetic effect, and also relaxes the smooth muscles of the internal organs and is a weak antiemetic. Its sedative effect is similar in strength to the effects of neuroleptics. In high doses, it also has a hypnotic effect.
Rapidly absorbed when taken orally, penetrates the blood-brain barrier. Its half-life is about 7 hours. Undergoes biotransformation in the liver, excreted by the kidneys.
It is used for all kinds of allergic diseases, as a sedative and hypnotic, as well as in the complex therapy of radiation sickness. Less commonly used for vomiting of pregnant women, seasickness.
Inside is prescribed in the form of tablets of 0.03-0.05 g 1-3 times a day for 10-14 days, or one tablet at bedtime (as a sleeping pill).
Intramuscularly injected 1-5 ml of a 1% solution, intravenous drip - 0.02-0.05 g of the drug in 100 ml of a 0.9% sodium chloride solution.
Can be used as eye drops, rectal suppositories or creams and ointments.
Side effects of this drug are: short-term numbness of the mucous membranes, headache, dizziness, nausea, dry mouth, weakness, drowsiness. Side effects go away on their own, after a dose reduction or complete discontinuation of the drug.
Contraindications are pregnancy, lactation, prostatic hypertrophy, angle-closure glaucoma.
Chloropyramine (suprastin)
It has antihistamine, anticholinergic, myotropic antispasmodic activity. It also has antipruritic and sedative effects.
Quickly and completely absorbed when taken orally, the maximum concentration in the blood is observed 2 hours after ingestion. Penetrates through the blood-brain barrier. Biotransformirovatsya in the liver, excreted by the kidneys and faeces.
It is prescribed for all kinds of allergic reactions.
It is used orally, intravenously and intramuscularly.
Inside should be taken 1 tablet (0.025 g) 2-3 times a day, with meals. The daily dose may be increased to a maximum of 6 tablets.
In severe cases, the drug is administered parenterally - intramuscularly or intravenously, 1-2 ml of a 2% solution.
When taking the drug, side effects such as general weakness, drowsiness, decreased reaction rate, impaired coordination of movements, nausea, dry mouth are possible.
Enhances the effect of hypnotics and sedatives, as well as narcotic analgesics and alcohol.
Contraindications are similar to those of diphenhydramine.
Clemastine (tavegil)
By structure and pharmacological properties, it is very close to diphenhydramine, but it acts longer (within 8-12 hours after administration) and is more active.
The sedative effect is expressed moderately.
It is used orally 1 tablet (0.001 g) before meals with plenty of water, 2 times a day. In severe cases, the daily dose can be increased by 2, maximum - 3 times. The course of treatment is 10-14 days.
It can be used intramuscularly or intravenously (within 2-3 minutes) - 2 ml of a 0.1% solution per dose, 2 times a day.
Side effects with this drug are rare. Headache, drowsiness, nausea and vomiting, constipation are possible.
Be wary appoint persons whose profession requires intense mental and physical activity.
Contraindications are standard.
Mebhydrolin (diazolin)
In addition to antihistamine, it has anticholinergic and. Sedative and hypnotic effects are extremely weak.
When taken orally, it is slowly absorbed. The half-life is only 4 hours. Biotransformed in the liver, excreted in the urine.
It is used orally, after meals, in a single dose of 0.05-0.2 g, 1-2 times a day for 10-14 days. The maximum single dose for an adult is 0.3 g, daily - 0.6 g.
Generally well tolerated. Sometimes it can cause dizziness, irritation of the gastric mucosa, blurred vision, urinary retention. In very rare cases - when taking a large dose of the drug - a slowdown in the rate of reactions and drowsiness.
Contraindications are inflammatory diseases of the gastrointestinal tract, angle-closure glaucoma and prostatic hypertrophy.
2nd generation antihistamines
Antihistamines of the second generation are characterized by high efficacy, rapid onset of action and a minimum of side effects, however, some of their representatives can cause life-threatening arrhythmias. The purpose of the development of drugs in this group was to minimize sedative and other side effects while maintaining or even stronger antiallergic activity. And it succeeded! Antihistamine drugs of the 2nd generation have a high affinity specifically for H1-histamine receptors, with virtually no effect on choline and serotonin receptors. The advantages of these drugs are:
- rapid onset of action;
- long duration of action (the active substance binds to the protein, which ensures its longer circulation in the body; in addition, it accumulates in organs and tissues, and is also slowly excreted);
- additional mechanisms of anti-allergic effects (suppress the accumulation of eosinophils in the respiratory tract associated with the intake of an allergen, and also stabilize mast cell membranes), causing a wider range of indications for their use (,);
- with prolonged use, the effectiveness of these drugs does not decrease, that is, there is no effect of tachyphylaxis - there is no need to periodically change the drug;
- since these drugs do not penetrate or penetrate in extremely small quantities through the blood-brain barrier, their sedative effect is minimal and is observed only in patients who are particularly sensitive in this regard;
- do not interact with psychotropic drugs and ethyl alcohol.
One of the most adverse effects of 2nd generation antihistamines is their ability to cause fatal arrhythmias. The mechanism of their occurrence is associated with blocking the potassium channels of the heart muscle with an antiallergic agent, which leads to a prolongation of the QT interval and the occurrence of arrhythmia (usually ventricular fibrillation or flutter). This effect is most pronounced in drugs such as terfenadine, astemizole and ebastine. The risk of its development increases significantly with an overdose of these drugs, as well as in the case of a combination of taking them with antidepressants (paroxetine, fluoxetine), antifungals (itraconazole and ketoconazole) and some antibacterial agents (antibiotics from the macrolide group - clarithromycin, oleandomycin, erythromycin), some antiarrhythmics (disopyramide, quinidine), when the patient consumes grapefruit juice and severe.
The main form of release of antihistamines of the 2nd generation is tableted, while parenteral ones are absent. Some drugs (such as levocabastine, azelastine) are available as creams and ointments and are intended for topical administration.
Consider the main drugs of this group in more detail.
Acrivastine (semprex)
Well absorbed when taken orally, begins to act within 20-30 minutes after ingestion. The half-life is 2-5.5 hours, it penetrates the blood-brain barrier in a small amount, is excreted in the urine unchanged.
Blocks H1-histamine receptors, to a small extent has a sedative and anticholinergic effect.
It is used for all kinds of allergic diseases.
Against the background of admission, in some cases, drowsiness and a decrease in the reaction rate are possible.
The drug is contraindicated during pregnancy, during lactation, with severe, severe coronary and, as well as children under 12 years of age.
Dimetinden (Fenistil)
In addition to antihistamine, it has a weak anticholinergic, anti-bradykinin and sedative effects.
It is quickly and completely absorbed when taken orally, while bioavailability (degree of digestibility) is about 70% (in comparison, when using cutaneous forms of the drug, this figure is much lower - 10%). The maximum concentration of the substance in the blood is observed 2 hours after ingestion, the half-life is 6 hours for the usual and 11 hours for the retard form. Through the blood-brain barrier penetrates, excreted in the bile and urine in the form of metabolic products.
Apply the drug inside and topically.
Inside, adults take 1 capsule of retard at night or 20-40 drops 3 times a day. The course of treatment is 10-15 days.
The gel is applied to the affected areas of the skin 3-4 times a day.
Side effects are rare.
Contraindication is only the 1st trimester of pregnancy.
Enhances the effect on the central nervous system of alcohol, sleeping pills and tranquilizers.
Terfenadine (histadine)
In addition to antiallergic, it has a weak anticholinergic effect. It does not have a pronounced sedative effect.
Well absorbed when taken orally (bioavailability delivers 70%). The maximum concentration of the active substance in the blood is observed after 60 minutes. It does not penetrate the blood-brain barrier. Biotransformed in the liver with the formation of fexofenadine, excreted in faeces and urine.
The antihistamine effect develops after 1-2 hours, reaches a maximum after 4-5 hours, and lasts for 12 hours.
Indications are the same as for other drugs in this group.
Assign 60 mg 2 times a day or 120 mg 1 time per day in the morning. The maximum daily dose is 480 mg.
In some cases, when taking this drug, the patient develops such side effects as erythema, fatigue, headache, drowsiness, dizziness, dry mucous membranes, galactorrhea (outflow of milk from the mammary glands), increased appetite, nausea, vomiting, in case of an overdose - ventricular arrhythmias.
Contraindications are pregnancy and lactation.
Azelastine (allergodil)
It blocks H1-histamine receptors, and also prevents the release of histamine and other allergy mediators from mast cells.
It is rapidly absorbed in the digestive tract and from the mucous membranes, the half-life is as long as 20 hours. Excreted as metabolites in the urine.
They are used, as a rule, for allergic rhinitis and.
When taking the drug, side effects such as dryness and irritation of the nasal mucosa, bleeding from it and taste disorders during intranasal use are possible; irritation of the conjunctiva and a feeling of bitterness in the mouth - when using eye drops.
Contraindications: pregnancy, lactation, children under 6 years of age.
Loratadine (lorano, claritin, lorizal)
Long-acting H1-histamine receptor blocker. The effect after a single dose of the drug lasts for a day.
There is no pronounced sedative effect.
When taken orally, it is absorbed quickly and completely, reaches a maximum concentration in the blood after 1.3-2.5 hours, and is half excreted from the body after 8 hours. Biotransformed in the liver.
Indications are any allergic diseases.
It is usually well tolerated. In some cases, dry mouth, increased appetite, nausea, vomiting, sweating, pain in the joints and muscles, hyperkinesis may occur.
Contraindication is hypersensitivity to loratadine and lactation.
Be wary appoint pregnant women.
Bamipin (soventol)
Blocker of H1-histamine receptors for local use. It is prescribed for allergic skin lesions (urticaria), contact allergies, as well as for frostbite and burns.
The gel is applied in a thin layer to the affected areas of the skin. After half an hour, it is possible to re-apply the drug.
Cetirizine (Cetrin)
Metabolite of hydroxyzine.
It has the ability to freely penetrate the skin and quickly accumulate in it - this leads to a rapid onset of action and high antihistamine activity of this drug. There is no arrhythmogenic effect.
It is rapidly absorbed when taken orally, its maximum concentration in the blood is observed 1 hour after ingestion. The half-life is 7-10 hours, but in case of impaired renal function, it is extended to 20 hours.
The spectrum of indications for use is the same as for other antihistamines. However, due to the characteristics of cetirizine, it is the drug of choice in the treatment of diseases manifested by skin rashes - urticaria and allergic dermatitis.
Take 0.01 g in the evening or 0.005 g twice a day.
Side effects are rare. This is drowsiness, dizziness and headache, dry mouth, nausea.
3rd generation antihistamines
III generation antihistamines have high antiallergic activity and are devoid of arrhythmogenic effect. These drugs are active metabolites (metabolites) of the previous generation. They are devoid of cardiotoxic (arrhythmogenic) effect, but retained the advantages of their predecessors. In addition, 3rd generation antihistamines have a number of effects that enhance their antiallergic activity, which is why their effectiveness in treating allergies is often higher than that of the substances from which they are produced.
Fexofenadine (Telfast, Allegra)
It is a metabolite of terfenadine.
It blocks H1-histamine receptors, prevents the release of allergy mediators from mast cells, does not interact with cholinergic receptors, and does not depress the central nervous system. It is excreted unchanged with feces.
The antihistamine effect develops within 60 minutes after a single dose of the drug, reaches a maximum after 2-3 hours, lasts for 12 hours.
Side effects such as dizziness, headache, weakness are rare.
Desloratadine (erius, edema)
It is an active metabolite of loratadine.
It has anti-allergic, anti-edematous and antipruritic effects. When taken in therapeutic doses, it practically does not have a sedative effect.
The maximum concentration of the drug in the blood is reached 2-6 hours after ingestion. The half-life is 20-30 hours. Does not penetrate the blood-brain barrier. Metabolized in the liver, excreted in the urine and feces.
In 2% of cases, against the background of taking the drug, headache, increased fatigue and dry mouth may occur.
In renal failure appoint with caution.
Contraindications are hypersensitivity to desloratadine. As well as periods of pregnancy and lactation.
Levocetirizine (Aleron, L-cet)
A derivative of cetirizine.
The affinity for H1-histamine receptors of this drug is 2 times higher than that of its predecessor.
Facilitates the course of allergic reactions, has anti-edematous, anti-inflammatory, antipruritic effect. Practically does not interact with serotonin and cholinergic receptors, does not have a sedative effect.
When taken orally, it is rapidly absorbed, its bioavailability tends to 100%. The effect of the drug develops 12 minutes after a single dose. The maximum concentration in blood plasma is observed after 50 minutes. It is excreted mainly by the kidneys. It is allocated with breast milk.
Contraindicated in case of hypersensitivity to levocetirizine, severe renal insufficiency, severe galactose intolerance, deficiency of the lactase enzyme or impaired absorption of glucose and galactose, as well as during pregnancy and lactation.
Side effects are rare: headache, drowsiness, weakness, fatigue, nausea, dry mouth, muscle pain, palpitations.
Antihistamines and pregnancy, lactation
Therapy of allergic diseases in pregnant women is limited, since many drugs are dangerous for the fetus, especially in the first 12-16 weeks of pregnancy.
When prescribing antihistamines to pregnant women, the degree of their teratogenicity should be taken into account. All medicinal substances, in particular anti-allergic ones, are divided into 5 groups depending on how dangerous they are to the fetus:
A - special studies have shown that there is no harmful effect of the drug on the fetus;
B - when conducting experiments on animals, no negative effects on the fetus were found, special studies on humans have not been conducted;
C - animal experiments have revealed a negative effect of the drug on the fetus, but it has not been proven in relation to humans; drugs of this group are prescribed to a pregnant woman only when the expected effect exceeds the risk of its harmful effects;
D - the negative effect of this drug on the human fetus has been proven, however, its administration is justified in certain life-threatening situations for the mother, when safer drugs were ineffective;
X - the drug is certainly dangerous for the fetus, and its harm exceeds any theoretically possible benefit to the mother's body. These drugs are absolutely contraindicated in pregnant women.
Systemic antihistamines during pregnancy are used only when the expected benefit outweighs the possible risk to the fetus.
None of the drugs in this group is included in category A. Category B includes drugs of the 1st generation - tavegil, diphenhydramine, peritol; 2nd generation - loratadine, cetirizine. Category C includes allergodil, pipolfen.
Cetirizine is the drug of choice for the treatment of allergic diseases during pregnancy. Loratadine and fexofenadine are also recommended.
The use of astemizole and terfenadine is unacceptable due to their pronounced arrhythmogenic and embryotoxic effects.
Desloratadine, suprastin, levocetirizine cross the placenta, and therefore are strictly contraindicated for pregnant women.
With regard to the lactation period, the following can be said ... Again, the uncontrolled intake of these drugs by a nursing mother is unacceptable, since no human studies have been conducted on the degree of their penetration into breast milk. If necessary, in these drugs, a young mother is allowed to take the one that is allowed to be taken by her child (depending on age).
In conclusion, I would like to note that even though this article describes in detail the most commonly used drugs in therapeutic practice and indicates their dosages, the patient should start taking them only after consulting a doctor!
A rare child is not allergic to various pathogens, some react painfully to certain products from birth, others to cosmetics or flowering plants, but thanks to new generation drugs - antihistamines for children, serious complications can be avoided. If timely measures are taken to eliminate childhood allergies, then acute processes will not turn into a state of chronic ailments.
What are antihistamines
A group of modern medicines that suppress the action of histamine (a neurotransmitter) is called antihistamines. When an allergen is exposed to the body, the mediator or organic compound histamine begins to be released from the connective tissue cells that make up the immune system. When a neurotransmitter interacts with specific receptors? often there is swelling, itching, rash and other manifestations of allergies. Antihistamines are responsible for blocking these receptors. Today there are four generations of these drugs.
Antiallergic drugs do not completely cure the disease. They do not particularly affect the cause of the allergy, but only help to cope with unpleasant symptoms. Such medications can be prescribed to patients of any age, even one-year-olds and infants. Antihistamines are prodrugs. This means that when they enter the body, they begin to be converted into active metabolites. An important property of these funds is the complete absence of a cardiotoxic effect.
Indications for use
When teething, before vaccination, special anti-allergic drugs can be used to neutralize a possible allergic reaction. Besides, indications for the use of such funds are:
- hay fever (pollinosis);
- angioedema;
- year-round, seasonal allergic reactions (conjunctivitis, rhinitis);
- skin itching in infectious chronic diseases;
- previously observed complex manifestations of allergies or symptoms of anaphylactic shock;
- atopic dermatitis, eczema, dermatosis, urticaria and other skin rashes;
- individual predisposition to allergies;
- deterioration of the child's condition with chronic respiratory ailments (laryngitis, stenosis of the larynx, allergic cough);
- a high level of eosinophils in the blood;
- insect bites;
- swelling of the mucous membranes of the nose, oral cavity;
- acute manifestations of allergy to drugs.
Classification
Antiallergic drugs, depending on the characteristics of the chemical composition, can be divided into groups:
- piperidine derivatives;
- alkylamines;
- alphacarboline derivatives;
- ethylenediamines;
- phenothiazine derivatives;
- piperazine derivatives;
- ethanolamines;
- quinuclidine derivatives.
Modern medicine offers a huge number of classifications of antiallergic drugs, but none of them is generally accepted. The classification of medicines by the time of their creation or by generations, which are currently distinguished by 4: 1 - sedative, 2 generation - non-sedative, 3 and 4 - metabolites, has received wider application in clinical practice.
Generations of antihistamines
The very first anti-allergic drugs appeared in the 30s of the 20th century - these were the 1st generation drugs. Science is constantly moving forward, so over time, similar tools of the second, 3rd and 4th generations were developed. With the advent of each new drug, the strength and number of side effects decrease, and the duration of exposure increases. Below is a table of 4 generations of antiallergic drugs:
| Generation | Main active ingredient | Characteristic | Titles |
| 1 | Diphenhydramine, diphenhydramine, diprazine, clemastine, hifenadine | They have a sedative effect, they have a short-term effect. Often Diphenhydramine is prescribed for hay fever, allergic dermatosis. Medicines cause tachycardia and vestibulopathy. | Psilo-balm, Suprastin, Tavegil, Diazolin |
| 2 | Azelastine, ebastine, astemizole, loratadine, terfenadine | Not sedative. There is no effect on the heart. Only one dose per day is needed, long-term use is possible. | Claritin, Kestin, Rupafin, Tsetrin, Ketotifen, Fenistil, Zodak |
| 3 | Cetirizine, fexofenadine, desloratadine | Active metabolites do not affect the functioning of the heart. Rarely cause dryness of the mucous membranes of the oral cavity. | Xyzal, Allegra, Desloratadine, Cetirizine, Telfast, Fexofast |
| 4 | Levocetirizine, desloratadine | Modern means that instantly affect the body. 4th generation drugs quickly block histamine receptors, effectively eliminate allergy symptoms. | Xizal, Glenset, Erius, Ebastin, Bamipin, Fenspiride |
Antiallergic drugs for children
The choice of antihistamines should be carried out by a doctor. Self-medication will only aggravate the allergic reaction that has appeared and cause undesirable consequences. For first aid, parents often use creams. They can be smeared with a reaction to the vaccine. Other forms: drops, tablets, syrup, suspension should be used after consulting a specialist. The pediatrician will select the dosage, taking into account the severity of the allergy and the age of the baby.
Up to a year
Usually, infants pediatricians prescribe a new generation of drugs, since the second and first can cause side effects: headache, drowsiness, suppression of activity, respiratory depression. Doctors often do not recommend taking antihistamines for babies, but sometimes in acute situations they are simply necessary. The best remedies for small patients are:
- Suprastin solution. It is used to treat the common cold, urticaria, acute allergic dermatitis. Well removes itching, accelerates the process of getting rid of rashes on the skin. Approved for the treatment of infants (from the age of 30 days). The children's dose is one fourth of the ampoule 2 times a day. Rarely, the medicine can cause nausea, stool disorders, dyspepsia. Suprastin is dangerous when taking more than one ampoule.
- Drops Fenistil. A popular allergy remedy for children is used to treat rubella, chickenpox. In addition, it is often drunk for contact dermatitis, sunburn, insect bites. Antihistamine drops for children Fenistil at the very beginning of treatment can cause drowsiness, but after a few days this effect disappears. The medicine has side effects: dizziness, muscle spasms, swelling of the oral mucosa. Children up to a year are prescribed once, 10 drops per day, but not more than 30.
From 2 to 5 years
When a child grows up, the range of medicines expands, although many well-known remedies are still contraindicated, for example, Suprastin and Claritin tablets, Azelastine drops. The most popular medications used from 2 to 5 years of age are:
- Drops of Tsetrin. It is used for food allergies, for the treatment of conjunctivitis and rhinitis. The advantage of using the drug is its long-term effect. Drops must be taken only once a day. Side effects: anticholinergic effect, drowsiness, headache.
- Erius. This allergy syrup for children is one of the most popular. It belongs to the drugs of the 3rd generation. Helps to stop allergic symptoms and alleviate the general condition of the patient. Not addictive. Erius syrup is useful for rhinitis, hay fever, allergic conjunctivitis, urticaria. Side effects: nausea, headache, diathesis, diarrhea.
From 6 years and older
As a rule, starting from the age of 6, a specialist can prescribe 2nd generation antihistamines for children. A child at this age is already able to take a tablet form, so allergists often prescribe Suprastin tablets. For allergic rhinitis and conjunctivitis, Allergodil drops are used. Besides, Patients over 6 years old can take:
- Tavegil. Recommended for hay fever, dermatitis, allergic insect bites. Among antiallergic drugs, Tavegil is considered the safest. Therapy for children from 6 to 12 years of age involves the following intake of funds - half a capsule in the morning and evening. Tablets should be taken regularly before meals, preferably at the same time. With caution, they should be taken by patients with glaucoma, because. Tavegil causes a deterioration in the clarity of perception of visual images.
- Zyrtec. These non-hormonal tablets have anti-inflammatory and antiexudative effects. The advantage of using the drug is its use as part of the combined treatment of bronchial asthma. Children from 6 years old can take half a tablet 2 times a day. Side effects: itching, rash, malaise, asthenia.
Which antihistamines are best for a child
Unstable children's immunity often contributes to the appearance of allergic reactions. Modern antihistamines for children help to cope with negative symptoms. Many pharmaceutical companies produce anti-allergic drugs in children's dosage in the form of syrup, drops, suspension. This facilitates the reception and does not cause the baby to be disgusted with the treatment. Often, a doctor may prescribe an antihistamine in the form of a gel or cream to reduce local inflammation. They are used externally for an allergic skin reaction to insect bites.
Usually, antihistamines for newborns are allowed to be given in the form of syrup or oral drops, and they should not use the old generation (1st) because of sedation and high toxicity. The dosage of drugs depends on the severity of the symptoms and the patient's body weight. Antiallergic drugs of the 3rd generation are recommended for children from one year old. For an older child, pills are more suitable. It is also possible to use anti-allergic local remedies: nasal sprays, eye drops, gels, creams, ointments.
Tablets
The most common form of release of anti-allergic drugs are tablets. A child can take them only from the age of 3, but often at this age the baby is not yet able to swallow the medicine. Therefore, you can give tablets in crushed form, diluting them with water. Popular tablets are:
- Loratadine. second generation drug. Helps to quickly eliminate the unpleasant symptoms of allergic rhinitis, reactions to pollen and flowering plants. It is used in the treatment of urticaria, bronchial asthma. Children from two years of age are recommended a single dose of 5 mg. Adolescents - 10 mg. Side effects: fever, blurred vision, chills.
- Diazolin. Helps with allergic seasonal rhinitis and cough. It can be prescribed during chickenpox, urticaria, conjunctivitis caused by pollen. The maximum daily dose of Diazolin in patients aged 2 to 5 years is 150 mg. It is not recommended to drink pills for heart problems.
Drops
This form is convenient for use in young children, it is easily dosed using a special bottle. As a rule, doctors try to prescribe antihistamines in drops for newborns. The most famous means are:
- Zodak. The tool has anti-exudative, antipruritic, anti-allergic action, prevents the further development of the disease. The action of the drug begins within 20 minutes after ingestion and persists throughout the day. Dosage for children from one year: 2 times a day, 5 drops. Rarely, against the background of the use of drops, nausea and dry mouth occur. Caution should be taken in patients with liver disease.
- Fenkarol. The drug relieves spasms, reduces suffocation, quickly extinguishes the negative manifestations of allergies. Patients under three years of age are recommended to give 5 drops 2 times a day. Fenkarol is prescribed for chronic and acute hay fever, urticaria, dermatosis (psoriasis, eczema). Side effects: headache, nausea, dry mouth.
syrups
Most antihistamines for children come in tablets, but some have alternatives in syrup form. Most of them have age limits up to two years. The most popular antihistamine syrups are:
- Claritin. It has a long anti-allergic effect. The remedy is suitable for eliminating acute symptoms, preventing severe relapses. After ingestion, the medicine will begin to act after 30 minutes. Claritin is prescribed for seasonal or year-round rhinitis, allergic conjunctivitis. Rarely, drowsiness and headache may occur while taking the medicine.
- Hismanal. The drug is prescribed for allergic skin reactions, for the treatment and prevention of angioedema. Doses of medication: for patients from 6 years old - 5 mg once a day, younger than this age - 2 mg per 10 kg. Rarely, the medication may cause nausea, headache, and dry mouth.
Ointments
Antiallergic children's ointments are a large group of medicines intended for topical use. Antihistamine ointments are applied to the affected area of skin manifestations of allergies. The most famous are:
- Bepanten. Ointment that stimulates tissue regeneration. It is used to care for babies, for skin irritations, diaper dermatitis, to relieve dry skin. Rarely, long-term treatment with Bepanthen causes itching and urticaria.
- Gistan. Non-hormonal antihistamine cream. It contains components such as string extract, violets, calendula. This topical medicine is used for allergic skin reactions and as a topical anti-inflammatory agent for atopic dermatitis. Contraindications: Do not use the ointment for children under one year old.
Overdose of antihistamines in children
Abuse, misuse or prolonged therapy with antiallergic drugs can lead to their overdose, which often manifests itself in the form of increased side effects. They are only temporary and disappear after the patient stops taking the medicine or is prescribed an acceptable dose. Usually, children with an overdose may experience:
- severe drowsiness;
- excessive stimulation of the central nervous system;
- dizziness;
- hallucinations;
- tachycardia;
- excited state;
- fever;
- convulsions;
- impaired renal function;
- dry mucous membranes;
- pupil dilation.
The price of antihistamines for children
Any antiallergic drugs and their analogues can be purchased at a pharmacy without a prescription or ordered online. Their cost depends on the manufacturer, dosage, form of release, pricing policy of the pharmacy and the region of sale. Approximate prices for antiallergic drugs in Moscow are presented in the table:
Medicines combined by the phrase " antihistamines”, are surprisingly common in home medicine cabinets. At the same time, the vast majority of people who use these drugs have no idea either about how they work, or about what the word “antihistamines” means in general, or about what all this can lead to.
The author with great pleasure would write in capital letters the slogan: “antihistamines should be prescribed only by a doctor and used in strict accordance with the doctor’s prescription,” after which he would put a bullet and close the topic of this article. But such a situation will be very similar to the numerous warnings of the Ministry of Health regarding smoking, so we will refrain from slogans and move on to filling gaps in medical knowledge.
So the occurrence
allergic reactions largely due to the fact that under the influence of certain substances ( allergens) in the human body, quite certain biologically active substances are produced, which, in turn, lead to the development allergic inflammation. There are dozens of these substances, but the most active of them is histamine. In a healthy person histamine is in an inactive state inside very specific cells (the so-called mast cells). Upon contact with an allergen, mast cells release histamine, which leads to allergy symptoms. These symptoms are very diverse: swelling, redness, rash, cough, runny nose, bronchospasm, lowering blood pressure, etc.
For quite a long time, doctors have been using drugs that can affect the metabolism of histamine. How to influence? Firstly, to reduce the amount of histamine released by mast cells and, secondly, to bind (neutralize) the histamine that has already begun to act actively. It is these drugs that are united in the group of antihistamines.
Thus, the main reason for using antihistamines
Prevention and/or elimination of allergy symptoms. Allergies to anyone and anything: respiratory allergies (they inhaled something wrong), food allergies (they ate something wrong), contact allergies (they were smeared with something wrong), pharmacological allergies (they were treated with what didn’t fit) .
Should be replaced immediately, that the preventive effect of any
a antihistamines is not always so pronounced that there is no allergy at all. Hence the quite logical conclusion that if you know a specific substance that causes an allergy in you or your child, then the logic is not to eat an orange bite with suprastin, but to avoid contact with the allergen, i.e. Do not eat orange. Well, if it is impossible to avoid contact, for example, you are allergic to poplar fluff, there are a lot of poplars, but they don’t give you a vacation, then it’s time to be treated.
The "classic" antihistamines include diphenhydramine, diprazine, suprastin, tavegil, diazolin, fenkarol. All these drugs have been used for many years.
The experience (both positive and negative) is quite large.
Each of the above drugs has many synonyms, and there is not a single well-known pharmacological company that would not produce at least something antihistamine, under its proprietary name, of course. The most relevant is the knowledge of at least two synonyms, in relation to drugs that are often sold in our pharmacies. We are talking about pipolfen, which is the twin brother of diprazine and clemastine, which is the same as tavegil.
All of the above drugs can be consumed by swallowing (tablets, capsules, syrups), diphenhydramine is also available in the form of suppositories. In severe allergic reactions, when a quick effect is needed, intramuscular and intravenous injections are used (diphenhydramine, diprazine, suprastin, tavegil).
We emphasize once again: the purpose of using all of the above drugs is one
Prevention and elimination of allergy symptoms. But the pharmacological properties of antihistamines are not limited to antiallergic action. A number of drugs, especially diphenhydramine, diprazine, suprastin and tavegil, have more or less pronounced sedative (hypnotic, sedative, inhibitory) effects. And the broad masses of people actively use this fact, considering, for example, diphenhydramine as a wonderful sleeping pill. From suprastin with tavegil, you also sleep well, but they are more expensive, so they are used less frequently.
The presence of antihistamines in the sedative effect requires special care, especially in cases where the person using them is engaged in work that requires a quick reaction, such as driving a car. Nevertheless, there is a way out of this situation, since diazolin and phencarol have very little sedative effects. It follows that for a taxi driver with an allergic rhinitis, suprastin is contraindicated, and fenkarol will be just right.
Another effect of antihistamines
The ability to enhance (potentiate) the action of other substances. General doctors use the potentiating action of antihistamines to enhance the effect of antipyretic and analgesic drugs: everyone knows the favorite mixture of emergency doctors - analgin + diphenhydramine. Any drugs that act on the central nervous system, in combination with antihistamines, become noticeably more active, an overdose can easily occur up to loss of consciousness, coordination disorders are possible (hence the risk of injury). As for the combination with alcohol, no one will undertake to predict the possible consequences, and it can be anything - from deep, deep sleep to very delirium tremens.
Diphenhydramine, diprazine, suprastin and tavegil have a very undesirable side effect
- "drying" effect on the mucous membranes. Hence the often occurring dry mouth, which is generally tolerable. But the ability to make sputum in the lungs more viscous is already more relevant and very risky. At least the thoughtless use of the four antihistamines listed above for acute respiratory infections (bronchitis, tracheitis, laryngitis) significantly increases the risk of pneumonia (thick mucus loses its protective properties, blocks the bronchi, disrupts their ventilation - excellent conditions for the reproduction of bacteria, pathogens of pneumonia) .
Effects that are not directly related to the antiallergic action are very numerous and are expressed differently for each drug. The frequency of administration and doses are varied. Some drugs are safe during pregnancy, others are not. The doctor is supposed to know all this, and the potential patient is supposed to be careful. Dimedrol has an antiemetic effect, diprazine is used to prevent motion sickness, tavegil causes constipation, suprastin is dangerous for glaucoma, stomach ulcers and prostate adenoma, fencarol is not desirable for liver diseases. Suprastin can be used by pregnant women, fencarol is not allowed in the first three months, tavegil is not allowed at all ...
With all the pros and cons
antihistamines all of the above drugs have two advantages that contribute to their (drugs) widespread. Firstly, they really help with allergies and, secondly, their price is quite affordable.
The latter fact is especially important, since pharmacological thought does not stand still, but it is also expensive. New modern antihistamines are largely devoid of the side effects of classic drugs. They do not cause drowsiness, they are used once a day, they do not dry out the mucous membranes, and the anti-allergic effect is very active. Typical representatives
Astemizole (gismanal) and claritin (loratadine). Here, knowledge of synonyms can play a very significant role - at least the difference in price between Nashensky (Kyiv) loratadine and non-Nashensky claritin will completely allow you to subscribe to the magazine "My Health" for six months.
In some antihistamines, the prophylactic effect significantly exceeds the therapeutic one, that is, they are used mainly for the prevention of allergies. Such agents include, for example, cromoglycate sodium (intal)
The most important drug for the prevention of asthma attacks. For the prevention of asthma and seasonal allergies, for example, to the flowering of certain plants, ketotifen (zaditen, astafen, bronitene) is often used.
Histamine, in addition to allergic manifestations, also enhances the secretion of gastric juice. There are antihistamines that act selectively in this direction and are actively used to treat gastritis with high acidity, peptic ulcer of the stomach and duodenum.
Cimetidine (Gistak), ranitidine, famotidine. I report this for completeness, since antihistamines are considered only as a means to treat allergies, and the fact that they can also successfully treat stomach ulcers will certainly be a discovery for many of our readers.
However, antiulcer antihistamines are almost never used by patients on their own, without a doctor's recommendation. But in the fight against allergies, mass experiments of the population on their bodies
Rather the rule than the exception.
Given this sad fact, I will allow myself some advice and valuable guidance for lovers of self-treatment.
1. Mechanism of action
antihistamines similar, but there are still differences. It often happens that one medicine does not help at all, and the use of another quickly gives a positive effect. In short, a very specific drug is often suitable for a particular individual, and why this happens is not always clear. At least, if there is no effect after 1-2 days of taking the drug, the drug should be changed, or (on the advice of a doctor) treated with other methods or drugs of other pharmacological groups.
2. Multiplicity of ingestion:
Fenkarol
3-4 times a day;
Diphenhydramine, diprazine, diazolin, suprastin
2-3 times a day;
2 times a day;
Astemizole, claritin
1 per day.
3. Average single dose for adults
1 tablet. I do not give children's doses. Adults can experiment on themselves as much as they like, but I will not contribute to experiments on children. Only a doctor should prescribe antihistamines for children. He will give you a dose.
4. Reception and food.
Phencarol, diazolin, diprazine
After meal.
Suprastin
While eating.
Astemizol
On an empty stomach in the morning.
Dimedrol, Claritin and Tavegil intake is fundamentally not connected with food.
5. Terms of admission. Basically, any
an antihistamine (of course, except for those used prophylactically) does not make sense to take more than 7 days. Some pharmacological sources indicate that you can swallow for 20 days in a row, others report that, starting from the 7th day of administration, antihistamines can themselves become a source of allergies. Apparently, the following is optimal: if after 5-6 days of taking the need for anti-allergic drugs has not disappeared, the medicine should be changed,
We drank diphenhydramine for 5 days, switched to suprastin, etc. - fortunately, there are plenty to choose from.
6. It makes no sense to use
antihistamines "just in case" along with antibiotics. If your doctor prescribes an antibiotic and you are allergic to it, stop taking it immediately. An antihistamine medicine will slow down or weaken the manifestations of allergies: we will notice later that we will have time to get more antibiotics, then we will be treated longer.
7. Reactions to vaccinations, as a rule, have nothing to do with allergies. So there is no need to prophylactically put tavegils-suprastins into children.
8. And the last. Please keep antihistamines away from children.
