antihistaminice

Antihistaminice, more commonly known as antihistamines, are a class of medications that counter the effects of histamine released during allergic reactions. The primary mechanism is antagonism of histamine H1 receptors, which reduces common symptoms such as sneezing, itching, nasal congestion, and hives. Some antihistamines also interact with other receptors, contributing to additional effects and side effects.

Antihistamines are divided into generations. First-generation agents (for example, diphenhydramine, chlorpheniramine, promethazine) cross the blood–brain barrier and often cause drowsiness and anticholinergic effects. Second-generation agents (cetirizine, loratadine, fexofenadine, desloratadine) are less sedating because they poorly cross the blood–brain barrier. Topical antihistamines (azelastine, olopatadine) provide targeted relief with minimal systemic effects.

Indications include allergic rhinitis, conjunctivitis, and chronic urticaria. They may also help with symptoms of atopic dermatitis and, in some cases, nausea or motion sickness (particularly older first-generation drugs). Formulations include oral tablets or liquids, nasal sprays, and eye drops.

Common adverse effects depend on generation. First-generation agents frequently cause drowsiness, dry mouth, blurred vision, urinary retention, and confusion in older people. Second-generation antihistamines are generally well tolerated with fewer sedative effects. Interactions include alcohol and other central nervous system depressants; some agents may interact with certain antibiotics or be cautioned in pregnancy or in people with glaucoma or urinary retention.

Antihistamines have a long history, with development beginning in the mid-20th century. They are among the most widely used over-the-counter drugs for allergic symptoms, with a broad range of formulations and indications across many health systems.