Blockers of histamine H1 receptors (abbreviated as AHP) have been serving humanity for about seventy years. They have always been in demand by medicine. Against this background, they have recently been used without a doctor's prescription, which is alarming. Most often, such blockers are used to treat allergic pathologies, however, they are often used in the complex treatment of diseases such as bronchitis, pneumonia and autoimmune processes, which, of course, contradicts modern knowledge about their origin.
Next, we consider in detail histamine H1 receptor blockers, find out what their characteristics are, and in addition, we find out which of them belong to the second generation.
Definition: what are receptor blockers?
H1 histamine receptor blockers are drugs. There are many medications that affect the release, and in addition, the dynamics, kinetics and metabolism of histamine. These, in particular, include physiological and inverse histamine agonists.
Historically, the term “antihistamines” refers to drugs that block H1-histamine receptors. Since 1937, when the antihistamine effect of the previously synthesized compound was first experimentally confirmed, developments are being carried out along with the improvement of therapeutic antihistamines. Now we turn to the consideration of the features of such medical devices.
Features of these funds
Numerous studies have shown that histamine, due to the action on the receptors of the human respiratory system, skin and eyes, causes characteristic allergy symptoms, and antihistamines that selectively block histamine H1 receptors can stop and prevent it.
Most antihistamines used have a number of pharmacological specific properties that characterize them as a separate group. These include effects in the form of antipruritic, decongestant, antispastic, anticholinergic, antiserotonin, sedative and local anesthetic properties, and in addition, the prevention of induced histamine bronchial spasm. Some of them are characterized not by histamine blockade, but by structural features.
Competitive inhibition mechanism
Antihistamines can block the effects of histamine H1 receptors through competitive inhibition mechanisms . But their affinity for these receptors is significantly lower compared to histamine. Therefore, these medications cannot displace the histamine, which is associated with the receptor.
They can only block released and unoccupied receptors. Accordingly, the H1 type of blockers is most effective for preventing an allergic reaction of an immediate nature, and in case of an already occurring reaction it prevents the release of a new portion of histamine.
By their chemical structure, most of these drugs are classified as amines soluble in fats, which have the same structure. Their core is represented by an aromatic or heterocyclic group. They have it connected with the help of a molecule of nitrogen, carbon or oxygen with an amino group. The nucleus determines the severity of antihistamine activity along with some of the properties of the substance. Knowing the composition, you can determine in advance the strength of the drug along with its effects, for example, it is possible to establish the ability to penetrate the blood-brain barriers. Next, we find out what types of medications are considered.
Types of Antagonists
There are several classifications of histamine H1 receptor antagonists, although not one of them is generally accepted today. According to one popular classification, antihistamines are divided into first and second generation drugs by the time they are created.
Drugs that block H1 histamine receptors related to the first generation are commonly called sedatives (based on the dominant side effect), in contrast to non-sedative drugs related to the second generation. At present, the third generation is also being allocated, which includes fundamentally new drugs in the form of active metabolites, which, in addition to showing the highest antihistamine activity, show the absence of sedative effects and cardiotoxic effects characteristic of second-generation drugs.
In addition, according to the chemical structure (which largely depends on the X-bond), antihistamines are divided into several categories: ethanolamines along with ethylenediamines, alkylamines, derivatives of quinuclidine, alfacarbolin, piperazine, phenothiazine and piperidine.
Consider histamine H1 blocker drugs in more detail.
First and second generation drugs
So, the first-generation drugs include medicines in the form of “Diphenhydramine”, “Benadril”, “Doxylamine”, “Antazolin”, “Mepiramin”, “Quifenadine”, “Sequifenadine”, “Suprastin” and others.
2 generations of histamine receptor H1 blockers include Akrivastin, along with Astemizole, Dimentinden, Oxotamide, Terfenadine, Loratadin, Misolastin, Soventol, Claritin, Kestin and others .
"Loratadine" as the most effective antihistamine of the second generation
A widely used second-generation drug is currently a drug called loratadine. The antihistamine effect of this medication reaches a maximum after eight to twelve hours. It lasts more than twenty-four hours. It is worth saying that this tool is well studied, and rarely causes adverse reactions in patients. Its dosage depends directly on age, and in addition, on body weight.
Active metabolite - what is it?
An active metabolite of histamine H1 blockers is the active form of the drug after the drug has been treated by the body. Most of the above medicines break down, as a rule, in the liver with the subsequent formation of active forms of metabolites, which play an extremely important role in the implementation of the necessary therapeutic effect. In case of impaired liver function, some drugs may accumulate in the human body, which will lead to a lengthening of the QT interval on the electrocardiogram with further development of ventricular pirouette tachycardia.
The main indications for the use of drugs
The main indication for prescribing such drugs to patients is a deviation in well-being due to the presence of various allergic reactions in the form of atopic dermatitis, allergic responses, urticaria, insect bites, etc. The peculiarity of these drugs is that they block histamine receptors in the body. Thanks to this mechanism, the release into the blood and tissue of biologically active components that are responsible for the development of allergic manifestations stops or decreases.
Thus, antihistamines are the most common group of medications for allergy therapy. These drugs block the histamine produced during allergic reactions. Therefore, if the clinical manifestations of allergies in humans are absent, then such medications should not be taken for prophylaxis, as they simply will have nothing to act on. This category of drugs is one of the oldest in the field of pharmacology. It is worth noting that the first of them were synthesized back in the forties of the last century. To date, there are already three generations of these drugs.