In Vitro CYP2D Inhibitory Effect and Influence on Pharmacokinetics and Pharmacodynamic Parameters of Metoprolol Succinate by Terminalia arjuna in Rats.

BACKGROUND: Terminalia arjuna Wight & Arn. (Combretaceae) is a tree having an extensive medicinal potential in cardiovascular disorders. T. arjuna bark extract has been reported to play a significant role as a cardiac stimulant for its beneficial effects in angina. Herb - drug interactions (HDI) are one of the most important clinical concerns in the concomitant consumption of herbs and prescription drugs. Our study was to investigate the in vitro CYP2D inhibition potential of Terminalia arjuna (T. arjuna) extracts in rat liver microsomes and to study the influence of aqueous bark extract of T. arjuna on the oral pharmacokinetics and pharmacodynamics of metoprolol succinate in rats. METHODS: The CYP2D inhibition potential of herbal extracts of T. arjuna was investigated in rat liver microsomes. Pharmacokinetic-pharmacodynamic interaction of aqueous extract of T. arjuna with metoprolol succinate was investigated in rats. RESULTS: The ethyl acetate, alcoholic & aqueous bark extracts of T. arjuna showed potent reversible non-competitive inhibition CYP2D enzyme in rat liver microsomes with IC50 values less than 40 µg/mL. Arjunic acid, arjunetin and arjungenin did not show significant inhibition of CYP2D enzyme in rat liver microsomes. Pharmacokinetic studies showed that aqueous bark extract of T. arjuna led to a significant reduction (P < 0.05) in AUC0-24h and Cmax of metoprolol succinate in rats, when co-administered. Pharmacodynamic studies reveal a significant reduction in therapeutic activity of metoprolol succinate on co-administration with aqueous bark extract of T. arjuna. CONCLUSION: Based on our in vitro and in vivo findings and until further clinical drug interaction experiments are conducted, the co-administration of drugs, especially those primarily cleared via CYP2D catalyzed metabolism, with T. arjuna extracts should be done with caution.