Histamine H1 receptor blockers (abbreviated as AGP) have been serving mankind for about seventy years. They have always been in demand in 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, let's take a closer look at H1 histamine receptor blockers, find out what their features are, and in addition, find out which of them belong to the second generation.
Definition: what are receptor blockers?
H1-histamine receptor blockers are drugs. There are many drugs that affect the release, and in addition, the dynamics, kinetics and metabolism of histamine. These include, in particular, physiological and inverse histamine agonists.
Historically, the term "antihistamines" refers to drugs that block H1-histamine receptors. Since 1937, when the antihistamine effect of a previously synthesized compound was first experimentally confirmed, developments have been underway along with the improvement of therapeutic antihistamine medications. Now let's move on to considering the features of such medical devices.
Features of these funds
Multiple studies have shown that histamine, due to its effects on the receptors of the human respiratory system, skin and eyes, causes the characteristic symptoms of allergies, and antihistamines that selectively block histamine H1 receptors can stop and prevent it.
Most of the antihistamine drugs 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 histamine-induced bronchial spasm. Some of them are characterized not by histamine blockade, but by structural features.
Mechanism of competitive inhibition
Antihistamine medications can block the effects of histamineH1 receptors on the mechanisms of competitive inhibition. But their affinity for these receptors is significantly lower compared to histamine. Therefore, these medicines cannot displace histamine, which is bound to the receptor.
They can only block released and unoccupied receptors. Accordingly, the H1 type of blockers is most effective in preventing an immediate allergic reaction, and in the event of a reaction that has already occurred, 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 core determines the severity of antihistamine activity along with some of the properties of the substance. Knowing the composition, it is possible to 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, find out what types of medications are divided into.
Types of antagonists
There are several classifications of histamine H1 receptor antagonists, although none of them is considered generally accepted today. According to one popular classification, antihistamine drugs are divided into drugs of the first andsecond generation.
Drugs that block H1 histamine receptors belonging to the first generation are usually called sedatives (based on the dominant side effect), in contrast to non-sedating drugs belonging to the second generation. Currently, the third generation is also being isolated, which includes fundamentally new drugs in the form of active metabolites, which, in addition to the highest antihistamine activity, exhibit the absence of sedative effects and the cardiotoxic effects characteristic of second-generation drugs.
In addition, according to the chemical structure (which largely depends on the X-bond), antihistamine drugs are divided into several categories: ethanolamines along with ethylenediamines, alkylamines, quinuclidine derivatives, alphacarboline, piperazine, phenothiazine and piperidine.
Let's consider H1 histamine receptor blockers in more detail.
First and second generation drugs
So, first-generation drugs include medical products in the form of Diphenhydramine, Benadryl, Doxylamine, Antazolin, Mepyramine, Quifenadine, Sequifenadine, Suprastin and others.
H1 histamine receptor blockers of the 2nd generation include Akrivastine along with Astemizole, Dimentinden, Oxotamide, Terfenadine, Loratadine, Mizolastine, Soventol, Claritin, "Kestin" and others.
Loratadine as the most effective second-generation antihistamine
Widely applicablethe 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 over 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?
The active metabolite of H1 histamine receptor blockers is the active form of the drug after the drug has been processed by the body. Most of the above drugs break down, as a rule, in the liver, followed by the formation of active forms of metabolites that play an extremely important role in the implementation of the necessary therapeutic effect. If liver functions are impaired, some drugs can accumulate in the human body, which will lead to a lengthening of the QT interval on the electrocardiogram with the further development of ventricular pirouette tachycardia.
Main indications for drug use
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. A feature of these drugs is that they blockhistamine receptors in the body. Thanks to this mechanism, the release of biologically active components into the blood and tissue, which are responsible for the development of allergic manifestations, stops or decreases.
Thus, the most common group of medications for the treatment of allergies are antihistamines. These drugs block histamine, which is produced during allergic reactions. Therefore, in the event that there are no clinical manifestations of allergy in a person, then such drugs should not be taken for prevention, since they simply will not have anything 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 in the forties of the last century. Today, there are already three generations of these medicines.
