Pharmacological Actions

1. Antihistaminic Actions:-they block histamine effects at various sites.
2. Other Effects: are independent of the antihistaminic effects and vary widely according to the drug used.

Most of them produce CNS depression resulting in sedation, drowsiness, inability to concentrate, and disturbances of coordination. But very few agents such as phenindamine may produce stimulation.Anti-motion sickness effects are exhibited by promethazine, diphenhydramine, and dimenhydinate.Promethazine and mepyramine have significant local anesthetic effect.Majority possess atropine-like effects.Some have central antimuscarinic actions which is useful in the treatment of Parkinsonism.

Pharmacokinetics:

They are well-absorbed following oral and parenteral administration. And are mainly metabolized by the liver; degradation products are removed in the urine.