The 4 types of antihistamines: characteristics and functions.

An explanation of the types of antihistamines used in medicine.

Today, allergies are considered to be almost pandemic. The incidence of these events of autoimmune nature is on the rise, as it is estimated that, Today, there are an estimated 20 million Allergy sufferersof whom at least 10 million have symptoms that recur on an annual basis. The outlook is not too encouraging, as the World Health Organization believes that by 2050, 50% of the population will suffer from some form of allergy.

According to the Clinical University of Navarra (CUN), an allergic reaction consists of our body's perception of a substance that is not harmful, known as an "allergen". When this allergen (latex, mites, animal epithelia, insect bites, food and many others) comes into contact with the host, the immune system reacts erroneously, producing a large number of IgE antibodies.

After the antibody binds to the allergen, mediators (including histamine) are released, causing the typical symptoms of an allergic condition. To prevent the symptoms from escalating once the immune system has been triggered, there are a number of drugs and strategies available. Here's what you need to know about everything you need to know about the types of antihistamines, including when to use them.including times of use.

What is the role of histamine in allergic reactions?

Before dissecting what an antihistamine is, it is necessary to explore the role of histamine in allergic reactions. Once IgE-antibody (allergen) binding has occurred, this imidazole amine is released, essential for the expression of immune reactions in the allergic setting..

The main job of this inflammatory mediator is to provoke arteriolar dilatation (hypotension), which in turn considerably increases vascular permeability. It also stimulates gastric acid secretion, plays an essential role in inflammatory processes, modulates intestinal contractions at the muscular level and has effects on heart rate. In other words, it is an autoimmune compound, but it also acts on intestinal motility and is a neurotransmitter of the central nervous system (CNS).

Thanks to it, the leukocytes involved in the allergic immune response can reach the zone of conflict earlier and trigger the local or systemic reaction.. Due to its activity, histamine is one of the main mediators in the allergic response, and that is why antihistamines arise with the focus on preventing its adhesion to key structures.

What are antihistamines and what types are there?

As the Oxford Languages dictionary indicates, an antihistamine is any substance that combats the effects of histamine in the body by blocking its key receptors.Antihistamines are usually consumed on a massive scale worldwide, as they are very cheap drugs, in many cases do not require a prescription (generic) and are effective in relieving nasal congestion, sneezing and itchy skin, all of which are symptoms associated with allergic and autoimmune processes.

These drugs act against histamine on two very marked fronts: preventing local inflammation (wheal response) and vasodilatation (flare response), by blocking histamine receptors or reducing the activity of their receptors at the nervous, vascular, muscular and endothelial levels. (flare response), by blocking histamine receptors or reducing the activity of their receptors at the nervous, vascular, muscular and endothelial levels. The following are the types of antihistamines, based on their pharmacological properties.

H1 antihistamines

As their name suggests, they are drugs that inhibit the action of the H1 receptor. inhibit the action of the H1 receptor, which is expressed in smooth muscle, vascular endothelial cells, the heart and the central nervous system (CNS). (CNS). It should be noted that two generations can be distinguished within this block of drugs.

First generation H1 antihistamines are lipophilic and can easily cross the blood-brain barrier (between the blood and the brain). Therefore, they are considered to have a sedative effect, and some pharmacological variants are even used to treat insomnia. On the other hand, second-generation H1 antihistamines are more specific and do not cross this barrier, so their side effects do not go through sedation and other anticholinergic processes.

2. H2 antihistamines

H2 antihistamines are drugs that block the action of histamine at the level of H2 receptors, this time in the parietal cells of the stomach, which decreases gastric acidity. Recall that histamine is essential for the immune response to an allergen, but by itself also modulates basic stomach functions (among many other biological elements).

H2 antihistamines, unlike the aforementioned, are used to treat peptic ulcers, dyspepsia, stress ulcers, gastroesophageal reflux and other conditions.. However, proton pump inhibitor drugs, especially omeprazole, are nowadays more widely conceived to address these conditions.

3. H3 antihistamines

As you can imagine, H3 antihistamines block the histamine H3 receptor, which is expressed primarily in the central nervous system and to some extent in the peripheral nervous system. Although it may seem similar to the H1 and H2 groups, nothing could be further from the truth: the former act at the peripheral level of the organism (although they cause sedation if they reach the brain environment), while the H3s work directly in the neuronal and encephalic environment.

Therefore, beyond allergies, H3s work directly in the neuronal and cerebral environment, beyond allergies, group 3 antihistamines are beginning to be used for neurological problems.The drugs have been shown to be effective in the treatment of a wide range of disorders, such as narcolepsy, Alzheimer's disease, attention deficit hyperactivity disorder (ADHD) and schizophrenia. However, at this point, medicine continues to investigate the properties of these drugs at the brain level.

4. H4 antihistamines

H4 antihistamines inhibit the activity of the H4 receptor, which appears to mediate neutrophil outflow. appears to mediate the outflow of neutrophils from the bone marrow and is part of the oral epithelium.. Not much more information about them is publicly available.

Side effects and contraindications

If you are here because of an allergic condition, you are interested in knowing the effect and synergy of the first and second generation H1 antihistamines, since the rest are used in other medical fronts, as you have seen.

On the other hand, first-generation H1 antihistamines have a clear sedative effect, as they cross the blood-brain barrier and interact with neurons in the brain.. For this reason, it is completely inadvisable to consume alcohol if you are under this pharmacological treatment: the depressant effects of both compounds together can be very dangerous.

Likewise, when using a first generation H1 antihistamine, it is recommended not to drive a car or operate heavy machinery.In other words, do not carry out any activity that entails dangers or requires special attention. If the patient is in any of these situations, it is much better to resort to second generation H1 antihistamines. Remember that these do not cross the blood-brain barrier and, therefore, do not cause such marked symptoms in the central nervous system (CNS).

In any case, second-generation drugs also have certain drawbacksAmong their side effects, headaches, cough, tiredness, sore throat and abdominal pain are reported. These are not very common reports in the general society, but it is necessary to expose them.

On the other hand, it should be noted that H2 antihistamines are usually well tolerated by the general population, but it should be remembered that their use is aimed at reducing the acidification of the gastric environment. To date, drugs such as omeprazole have been shown to be more effective (and with fewer adverse effects) than these drugs.

Summary

As you have seen, the world of antihistamines goes far beyond allergy avoidance. Histamine is a compound that plays an essential role in the immune reaction to the presentation of an allergen, but it also modulates intestinal motility, gastric acid secretion and even certain circuits in the brain (as it is a neurotransmitter).

For all these reasons, antihistamines have a promising future, especially if we look at the H3 family. If given the right guidelines and modifications, these could become the answer to treating diseases such as Alzheimer's or disorders such as ADHD. Only time and science will tell.