This lack of receptor selectivity is the basis of the poor tolerability profile of some of these agents, especially when compared with the second-generation HDiphenhydramine was the prototypical agent in this group.Significant anticholinergic adverse effects, as well as sedation, are observed in this group but the incidence of gastrointestinal adverse effects is relatively low.

non sedating allergy medicine-2

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.

Multiple daily doses are required to provide 24-hour relief.

In school-age children, this may be a major disadvantage. Seasonal allergic rhinitis and antihistamine effect on children's learning.

The second-generation H receptors and cholinergic receptors.

This selectivity significantly reduces the occurrence of adverse drug reactions, such as sedation, while still providing effective relief of allergic conditions.

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.

They are effective in the relief of allergic symptoms, but are typically moderately to highly potent muscarinic acetylcholine receptor (anticholinergic) antagonists as well.