Antihistamines are medicines used to treat allergy symptoms. This group of drugs inhibits the effects produced by histamine.
Histamine is involved in many physiological processes in the body by binding to different receptors when it detects a foreign allergen. Antihistamines inhibit H1 receptors.
What are they used for?
Allergy antihistamines are used to treat symptoms caused by the action of histamine: rhinitis, allergic conjunctivitis, hives, itchy skin from various causes, irritative coughs, insect bites, colds, nausea and dizziness, poor appetite and minor sleep problems.
Types of antihistamines for allergies
There are many different antihistamines marketed to treat allergy symptoms, with very different compositions, mechanisms of action and side effects. The physician will determine which is the most appropriate for each type of allergy according to the patient.
From a clinical point of view, antihistamines are classified into two groups:
Classical or first-generation antihistamines: these are molecules that penetrate well into the CNS and are not very selective in their actions. They are used mainly for allergic rhinoconjunctivitis, itching, urticaria, coughing, nausea, prevention of motion sickness and insomnia. They are rapidly metabolised, so the dosage is usually 3 or 4 times a day.
Non-sedative or second-generation antihistamines: these are drugs derived from the previous ones, but with a more selective action and less distribution. They are used for allergic rhinoconjunctivitis and urticaria and are the first choice in these cases, but not for other purposes (dizziness, insomnia, etc.). They are usually taken once a day.
Most common antihistamines
The most commonly used first-generation antihistamines are:
Hydroxyzine, used as an antihistamine and as a tranquilliser.
Chlorpheniramine and its analogue, dexchlorpheniramine, available orally, topically and by injection.
Diphenhydramine, used as both a sleep inducer and an antihistamine, and available in many countries by mouth and injection; and its derivative dimenhydrinate, used for motion sickness.
Promethazine, also used to prevent and treat nausea and dizziness, and also available orally and intravenously.
Azatadine and its derivative cyproheptadine, the antihistamine most commonly used in years past as an appetite stimulant.
Ketotifen, most commonly used in children, and available orally and in eye drops.
What are the best antihistamines? There are many other first-generation antihistamines, most of which are part of over-the-counter anti-catarrhal compounds (Bronchostop, Frenadol, Vincigrip, etc.). Doxepin, an antidepressant with a potent antihistamine and sedative action, is still used for some indications of classical antihistamines.
The most commonly used second-generation antihistamines are: bilastine, cetirizine, desloratadine, ebastine, fexofenadine, levocetirizine, loratadine, mequitazine, mizolastine and rupatadine, all of which are taken orally in capsule or syrup form. In addition, there are several marketed only topically, in eye drops and/or nasal sprays, such as alcaftadine, azelastine, bepotastine, emedastine, levocabastine or olopatadine.
Can antihistamines be taken in pregnancy?
At present, taking antihistamines in pregnancy is not considered 100% safe, regardless of the active substance chosen. Therefore, before using these drugs, you should try to reduce the symptoms with other means, such as avoiding the allergen causing the symptoms, seawater irrigators, saline solution, and if necessary, you should consult your doctor to see what recommendations he/she makes in this regard. First generation antihistamines are usually used as antiemetics to counteract nausea.
Can antihistamines and alcohol be taken together?
Alcohol is not recommended when taking antihistamines, as it can cause dizziness and drowsiness, increasing the risk of overdose and causing accidents.
Antihistamines and side effects
Antihistamines act on the central nervous system, which can cause various side effects such as drowsiness, tiredness, blurred vision, constipation, etc.
First generation antihistamines tend to produce more adverse effects, and some, such as Dormidine, whose active ingredient is an antihistamine, are normally used to produce drowsiness in cases of occasional insomnia.
Is it possible to buy antihistamines without a prescription?
Yes, it is possible to buy antihistamines without prescription at Farmaciasdirect.com, where you can find the best brands of antihistamines, both general (reactine, Bactil, Rino Ebastel), and eye (alergoftal, reactine) and skin (fenergan, fenistil) antihistamines.
