Evaluation of six antihistamines in vitro and in patients with urticaria

ABSTRACT

Six commonly prescribed antihistamines have been ranked according to their relative potencies in blocking H₁ and muscarinic receptors by an in vitro method on the myenteric plexus-longitudinal muscle preparation of the guinea pig ileum. Calculation of the ratios of K_e against acetyl choline to K_c against histamine suggested that mepyramine was the drug which discriminated most clearly between histamine H₁ and acetyl choline receptors.

In contrast, using a self-assessment method in patients with chronic urticaria, cyproheptadine was the highest ranked antihistamine in terms of both effectiveness and relative freedom from side-effects. It is concluded that in vitro evaluation of antihistaminic and antimuscarinic potencies may produce misleading results in terms of clinical usefulness of a given antihistamine.