Background:

Mequitazine is a potent, nonsedative and long-acting histamine H1 antagonist.

Mequitazine is a potent H1-receptors selective antihistaminic drug widely studied and used for allergic disorders such as hay fever and urticaria[1]. Mequitazine demonstrates significant bactericidal effects against all the tested clinical isolates including Ps. aeruginosa. Its effect against the Gram-positive isolates is more pronounced[2].

Mequitazine and clemizole antagonize the effect of histamine in guinea-pig ileum competitively. Mequitazine at 107 produces a parallel shift of the dose-response curve to acetylcholine in the rat duodenum. Mequitazine at highest concentration shows anticholinergic activity[3]. Mequitazine inhibits contractile responses to KCl, phenylephrine (PE), 5-hydroxytryptamine (5-HT), and Ca2+ in rat aorta[4].

[1]. Gonnot V, et al. Expedient synthesis of mequitazine an antihistaminic drug by palladium catalyzed allylic alkylation of sodium phenothiazinate. Chem Pharm Bull (Tokyo). 2009 Nov;57(11):1300-2. [2]. El-Nakeeb MA, et a. In vitro antibacterial activity of some antihistaminics belonging to different groups against multi-drug resistant clinical isolates. Braz J Microbiol. 2011 Jul;42(3):980-91. [3]. Martinez-Mir I, et al. Antihistaminic and anticholinergic activities of mequitazine in comparison with clemizole. J Pharm Pharmacol. 1988 Sep;40(9):655-6. [4]. Satake N, et al. Possible mechanisms of vasoinhibitory effects of mequitazine, an antiallergic agent, on the contractions of isolated rat aorta induced by K+, phenylephrine, 5-hydroxytryptamine, and Ca2+. J Cardiovasc Pharmacol. 1994 Apr;23(4):669-73.