anti- histamines

Antihistamines are medications designed to block the action of histamine, a molecule that our body produces in excess during an allergic reaction.

These drugs are available in the form of tablets, solutions, nasal sprays, eye drops, and creams for topical application. Depending on the mode of administration, the type of molecule, and the pharmaceutical form, they may be sold with or without a prescription, but it is always advisable to consult with your doctor.

Their action can take effect within 15-30 minutes of intake, reaching maximum effectiveness in 1-2 hours. New-generation antihistamines often have a prolonged effect lasting up to 24 hours, therefore requiring a single daily administration.

How do they work?

Histamine acts by interacting with certain receptors called H1, H2, and H3. Specifically, antihistamines hinder its interaction with H1 receptors by binding to them instead of histamine.

There are several generations of antihistamines available on the market, ranging from the first to the third. The latest ones have a higher affinity for H1 receptors compared to first-generation ones, resulting in a lower risk of side effects such as confusion, drowsiness, dry mouth, and dizziness.

Histamine H1 Receptor Antagonists

First-generation antihistamines, in particular, are those that may present more side effects due to their interaction with other receptors not involved in the allergic response. These drugs are often used for the treatment of motion sickness and vestibular system disorders.

Among the most well-known medications containing first-generation active ingredients is Polaramin syrup, which in the past was frequently used as an ‘unofficial’ remedy to promote sleep in children, precisely because of its most notable side effect, drowsiness.

First-generation antihistamines are still used within medications not specifically intended for allergy treatment. For example, diphenhydramine is contained in the ‘night’ tablets of the popular drug ‘Actigrip day and night’.

Second-generation Histamine H1 Receptor Antagonists

These drugs exhibit greater selectivity towards the H1 receptor, thus reducing side effects. Among them, we can mention cetirizine (Zyrtec), loratadine (Claritin), desloratadine (Aerius), ebastine (Kestine), and finally ketotifen, which is found in both systemic and ophthalmic formulations.

Third-generation Histamine H1 Receptor Antagonists

They are the most recent, having high receptor affinity and minimal side effects. Among these, we find fexofenadine (Telfast, Fexallegra) and levocetirizine (Xyzal).

It is important to remember that, if one deems it necessary to take an antihistamine, it is always necessary to consult one’s doctor, especially:

During pregnancy and breastfeeding
In the case of prostate conditions
In conditions of hypertension and/or cardiovascular disorders
In the presence of thyroid, renal, and/or hepatic disorders
In the presence of urinary tract obstructions
In the presence of glaucoma

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