Antihistamines: what they are, how they act and what they cure

Antihistamines, what they are, how they act and what they cure.

They have names that are difficult to pronounce and remember – loratadine, desloratadineoxatomidepromethazine and xylometazoline just to name a few – but many know what they are: antihistamines are widely used drugs, a real lifeline for those who every year find themselves struggling with annoying seasonal allergies And for those who, on the other hand, must constantly deal with intense tearing, nose obstruction, sneezing and itching triggered by the encounter with dust mites or other allergens.

The allergy in addition to being annoying, can manifest itself in some cases with very strong symptoms, to the point of becoming a debilitating disorder. Especially during the spring season, when pollen invades the air we breathe, antihistamines represent much more than a lifeline for many people; The only way to spend time outdoors without incurring disturbances.

Their function is precisely to block the symptoms of allergic reactions triggered by an immune system that from a fundamental ally of well-being turns into the cause of health problems.

In fact, allergies represent the most common example of disease attributable to the malfunction of the immune system and, in fact, represent the most common immune diseases.

The underlying cause is the response triggered by the immune defenses when they come into contact with foreign agents – the “allergens” – which in reality are not dangerous to health and therefore should not induce any defense response.

As it is easy to understand, when the immune system takes action to counteract allergens, it initiates an inflammatory response, which can be either local, as in the case of itching, swelling or nasal congestion, or more extensive. It is precisely inflammation that is the cause of the symptoms that allergy sufferers are used to knowing very well.

The pollen responsible for the most classic seasonal allergy (such as spring allergies) and dust mites are just two of these foreign agents, the list of which also includes several other factors normally found in nature, such as mold, wheat and milk proteins.

To avoid the problem it is necessary to avoid contact with the allergen that triggers this hypersensitivity reaction – for example, in the case of food allergies, excluding foods containing it from the diet.

Unfortunately, however, sometimes – as it is for example in the case of pollen allergies – being able to do so is almost impossible and the symptoms of allergy return to strike whenever you are face to face with the substances that trigger them.

In these cases the only way to feel better is to act on these symptoms and only an antihistamine can be able to give at least temporary relief.

There are also cases in which the same allergen is contained, for example, both in a plant and in a certain food: in this case we speak of cross-allergies. Here are some examples.

Plant Alimony
Grasses Tomato, kiwi, watermelon, peanut, wheat flour
Ambrosia Watermelon, melon, banana
Composite Celery, fennel, carrot, green pepper, parsley, chicory, chamomile
Parietaria Cherries, melon and basil

The causes of allergies

The appearance of an allergy is partly attributable to genetic factors and to an even greater extent to factors of environmental origin.

The phenomenon of atopy (i.e. the genetic predisposition to the development of allergies) has in fact been known for some time, but the strong spread of this type of problem in the Western world has brought the environment into the spotlight, revealing the role it can play in the development of allergies.

Today, among the main accused of their promotion are air pollution and improved hygienic conditions, which would lead the immune system to lose control of the production of a particular class of synthesized antibodies when the immune defenses come into contact with an external agent – immunoglobulins E (IgE) on which some of the tests used to diagnose allergies are also based.

IgE binds to specific elements present in mucous tissues in contact with the external environment without triggering particular symptoms. Continuous exposure to the external agent, however, leads to the amplification of IgE production, increasing the risk that inflammation ends up becoming chronic.

It is therefore evident that the modern lifestyle, and especially the Western one, has mainly influenced the onset of allergies among the population. The increasing pollution of air and water certainly plays a very important role, but also the high frequency of washing and the use of detergents and disinfectants that are too aggressive are not to be underestimated. These elements have played a very important role in the prevention of diseases and in the improvement of living conditions, but at the same time they could also be protagonists of the increase in the frequency of the most common allergies.

Symptoms to fight

Clinically, symptoms of allergies can involve skin, eyes, nose, bronchi and digestive system.

Among the most frequent are itchy skin, eyes, nose, mouth, throat or palate, acute hives, eye redness and profuse tearing, nasal congestion or watery discharge, sneezing, coughing, shortness of breath or wheezing or difficulty breathing, nausea, vomiting, stomach cramps or diarrhea.

Only in rarer cases (usually associated with taking drugs, insect bites or ingesting foods to which you are allergic) the encounter with the allergen can trigger an anaphylactic shock, ie a response that involves the whole body and that if not treated quickly can be fatal.

Symptoms of anaphylactic shock include acute asthma, generalized urticaria, bloating, and abdominal pain associated with vomiting and diarrhea. In their presence it is essential to administer adrenaline, a drug that those who know they are at risk of reactions of this type should always carry with them.

Fortunately, in most cases allergies trigger symptoms that do not put your health in immediate danger. However, even these problems can significantly undermine the quality of life. Just think of those who love outdoor sports: an allergy to pollen could literally make it impossible to train during periods when they invade the air.

In these cases the solution is neither antibiotics nor vitamins or remedies that help to deal with the classic cold, but antihistamines, available in different formulations – from sprays to eye drops, passing through products in the form of creams or ointments, designed for topical use, and for tablets to be taken orally – based on different effective active ingredients that can also be purchased without the need for a prescription or prescription.

This does not mean that antihistamines, like all drugs, can have side effects. For this reason it is essential to always consult with your doctor or pharmacist, who will be able to indicate the most suitable therapy based on the type of allergic reaction and the symptoms encountered.

What are antihistamines

The term “antihistamines” generally refers to a group of drugs used to relieve respiratory (rhinitis, asthma), eye (conjunctivitis) or skin (itching, redness, swelling) symptoms of allergic reactions. In fact, the class of antihistamines includes all molecules that act by counteracting the effects of histamine to varying degrees.

Histamine is a chemical mediator that acts in many districts of the body (skin, gastrointestinal tract, respiratory tract, heart, nervous system) binding to different types of receptors located on the surface of cells (against which they act as specific antagonists) and producing different effects.

Of the five types of receptors identified so far, indicated as H1, H2, H3, H4 and H-IC, the most important from a pharmacological point of view are H1, involved in inflammatory and allergic reactions, and H2, involved in acid secretion of the stomach.

Among the antihistamine drugs in use are therefore the two distinct groups of H1 blockers and H2 blockers.

How they work

Antihistamines bind to cellular histamine receptors, counteracting the action of histamine.

As mentioned, in fact, it has been observed that histamine and in particular the H1 receptor, is primarily involved in inflammatory and allergic reactions. As a result, this receptor also plays a leading role in the onset of symptoms and various problems related to allergies, both in nutrition and respiratory reactions.

If counteracted, the action of histamine can be harmless and therefore interrupt the inflammatory process that weakens the most sensitive subjects.

What are they?

Among the H1 blockers, first and second generation molecules are distinguished, which differ essentially in the different degree of specificity of their pharmacological action.

The first H1 blockers (diphenhydramine, chlorpheniramine, triprolidine) can overcome the blood-brain barrier and have some affinity for receptors of the neurotransmitter acetylcholine so they also have effects on the nervous system, such as sedation.

Precisely for this reason this type of antihistamine and its active ingredients are accused of creating drowsiness, which in turn can lead to some discomfort. For example, drowsiness could lead to subsequent drops in attention or concentration, or to having difficulty driving, especially if the antihistamine is taken in large doses.

Subsequently, the second generation molecules (cetirizine, mizolastine, loratadine, terfenadine, fexofenadine) were developed, more selective for H1 receptors and unable to penetrate the central nervous system, and therefore free of the undesirable effects of the previous ones.

The most modern antihistamines therefore, such as the aforementioned loratidine and cetirizine, have a reduced ability to create drowsiness, almost irrelevant if taken at a suitable and controlled dosage. The latter also helps to better control other types of side effects, which remain minor.

H2 blockers (cimetidine, ranitidine, famotidine, nizatidine, roxatidine) bind to H2 receptors present on gastric mucosa cells specialized in the production of hydrochloric acid.

They prevent histamine from stimulating these cells and, as a result, reduce the production of acid in the stomach.

Who cares what

H1 blockers (especially second-generation ones) are mainly used in the treatment of allergic symptoms. They do not prevent the allergic response from occurring, but prevent the effects produced by histamine that is released during the allergic reaction (mainly, vasodilation, increased permeability of capillaries, contraction of bronchial muscles).

A latest generation antihistamine is therefore more suitable for the treatment of the most common symptoms, such as coughrunny nose and rhinitis. For the latter ailment, you can find antihistamines of anti-H1 type in the form of nasal creams or sprays.

First-generation drugs are now used as sedatives or antiemetics or as decongestants for local use.

H2 blockers are used in the treatment of gastric ulcer and gastroesophageal reflux, with the aim of reducing acidity within the stomach. In this way, it is also possible to effectively counteract nausea and lack of appetite, generally very common symptoms in this condition.

Side effects of antihistamines

Like most other drugs, antihistamines are not without side effects either. Their list includes dizziness, dry mouth, nervousness, excitement or irritability, visual disturbances (which may for example become blurred) and reduced appetite. All these symptoms are more likely to occur especially in case of overdose or excessively prolonged use.

More specifically, first-generation H1 blockers can induce drowsiness, fatigue, dry mouth, urinary retention, visual disturbances, gastrointestinal disorders (nausea, diarrhea or constipation). These last symptoms can lead the patient to experience pain, even persistent, making daily activities difficult.

Among second-generation ones, terfenadine can, although rarely, cause cardiac arrhythmias.

Among H2 blockers, the most recent have infrequent and modest side effects. The older ones, cimetidine and ranitidine, can cause endocrine imbalances with antiandrogenic effects in men (impotence, decreased sperm, gynecomastia and galactorrhea).

Fortunately, though, it’s rare for an antihistamine to cause liver damage, especially if it’s used in low doses for limited periods of time. However, it is important to remember that any medicine or even supplements could interfere, even if only partially, with the action of antihistamines and with the risk of new side effects.

Before going to the pharmacy, therefore, it is very important that your general practitioner or your trusted allergist have carried out an accurate check, so as to be able to recommend the most suitable drug. Their advice will be of paramount importance for proper prevention of all allergic symptoms.

Contraindications

In general, the antihistamine is considered a safe remedy for adults, and in most cases it can also be taken by children who have reached two years of age.

However, it is always good to consult with the pediatrician before administering drugs to a child, as well as it is good to check with the help of your doctor or pharmacist which medicines or health conditions could represent a contraindication to taking antihistamines at any age.

In particular, it is good to talk to your doctor before taking an antihistamine during pregnancy or breastfeeding, but not only: knowing how to take antihistamines correctly can always help reduce side effects. The same precautions should also be taken during menopause, where the dosage may need to change.

Avoiding, for example, the intake of drugs that could interfere with their liver metabolism reduces the appearance of side effects at the cardiac level. You may also need to take precautions if you suffer from glaucoma, enlarged prostate or problems urinating, epilepsy, hyperthyroidism, cardiovascular disease, high blood pressure or diabetes.

Obviously, even products with local action must be carefully evaluated before taking an antihistamine or a specific drug. So pay attention to gels and creams for hands and face, some types of deodorants, specific supplements including lactic fermentssunscreens and after sunantifungal products. Especially in the most sensitive patients, any external substance could cause mild allergic reactions or interference with the action of antihistamines.

Joycelyn Elders is the author and creator of EmpowerEssence, a health and wellness blog. Elders is a respected public health advocate and pediatrician dedicated to promoting general health and well-being.

The blog covers a wide range of topics related to health and wellness, with articles organized into several categories.

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