Non sedating second and third generation antihistamines

Agents where the main therapeutic effect is mediated by negative modulation of histamine receptors are termed antihistamines; other agents may have antihistaminergic action but are not true antihistamines.

In type I hypersensitivity allergic reactions, an allergen (a type of antigen) interacts with and cross-links surface Ig E antibodies on mast cells and basophils.

The most common adverse effect is sedation; this "side-effect" is utilized in many OTC sleeping-aid preparations.

Once released, histamine can react with local or widespread tissues through histamine receptors.Infrequent adverse effects include urinary retention, palpitations, hypotension, headache, hallucination, and psychosis.-receptors and have a better tolerability profile compared to the first-generation agents.The most common adverse effects noted for second-generation agents include drowsiness, fatigue, headache, nausea and dry mouth.-antihistaminergic drugs and are relatively inexpensive and widely available.The authors of the American College of Chest Physicians Updates on Cough Guidelines (2006) recommend that, for cough associated with the common cold, first-generation antihistamine-decongestants are more effective than newer, non-sedating antihistamines.First-generation antihistamines include diphenhydramine (Benadryl), carbinoxamine (Clistin), clemastine (Tavist), chlorpheniramine (Chlor-Trimeton), and brompheniramine (Dimetane).