N-desmethyl Azelastine is an active metabolite of the histamine H₁receptor antagonist azelastine .^1,2It is formed from azelastine primarily by the cytochrome P450 (CYP) isoforms CYP3A4 and CYP2D6 and, to a lesser extent, by CYP1A2.²N-desmethyl Azelastine (1 µM) inhibits acetylcholine-induced depolarization and contractions in isolated human tracheal smooth muscle.¹It also inhibits transport of daunorubicin and digoxin in LLC-GA5-CoL150 cells overexpressing P-glycoprotein (P-gp), also known as multidrug resistance protein 1 (MDR1; IC₅₀s = 11.8 and 41.8 µM, respectively).³

1.Richards, I.S., Miller, L., Solomon, D., et al.Azelastine and desmethylazelastine suppress acetylcholine-induced contraction and depolarization in human airway smooth muscleEur. J. Pharmacol.186(2-3)331-334(1990) 2.Nakajima, M., Nakamura, S., Tokudome, S., et al.Azelastine N-demethylation by cytochrome P-450 (CYP)3A4, CYP2D6, and CYP1A2 in human liver microsomes: Evaluation of approach to predict the contribution of multiple CYPsDrug Metab. Dispos.27(12)1381-1391(1999) 3.Katoh, M., Nakajima, M., Yamazaki, H., et al.Inhibitory effects of CYP3A4 substrates and their metabolites on P-glycoprotein-mediated transportEur. J. Pharm. Sci.12(4)505-513(2001)