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).However, a 1955 study of "antihistaminic drugs for colds," carried out by the U. Army Medical Corps, reported that "there was no significant difference in the proportion of cures reported by patients receiving oral antihistaminic drugs and those receiving oral placebos.
The most common adverse effect is sedation; this "side-effect" is utilized in many OTC sleeping-aid preparations.
Other common adverse effects in first-generation H-antihistamines include dizziness, tinnitus, blurred vision, euphoria, uncoordination, anxiety, increased appetite leading to weight gain, insomnia, tremor, nausea and vomiting, constipation, diarrhea, dry mouth, and dry cough.
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.
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 common use, the term "antihistamine" refers only to H 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.
Once the mast cell-antibody-antigen complex is formed, a complex series of events occurs that eventually leads to cell degranulation and the release of histamine (and other chemical mediators) from the mast cell or basophil.
Once released, the histamine can react with local or widespread tissues through histamine receptors.
Histamine, acting on H-antihistamines help against these effects, they work only if taken before contact with the allergen.
In severe allergies, such as anaphylaxis or angioedema, these effects may be of life-threatening severity.