Evaluation of cytochrome P450 2D6 phenotyping in healthy adult Western Indians

BACKGROUND: Cytochrome P450 2D6 (CYP2D6) metabolizes around 25% of the drugs used in therapeutics and different polymorphisms have been identified in various populations. This study aimed at finding the prevalence of CYP2D6 polymorphisms using dextromethorphan as a probe drug. MATERIALS AND METHODS: Healthy participants were administered 60 mg dextromethorphan after an overnight fast and 5 ml of blood was collected 3 h postdose. A validated laboratory method was used to measure both dextromethorphan and its active metabolite, dextrorphan from plasma. Metabolic ratio (MR) of dextromethorphan to dextrorphan was calculated for each of the participants. Probit analysis was done and antimode was defined. Individuals with log MR equal to or higher than the antimode were classified as poor metabolizers (PMs) and those with values less than antimode were categorized as extensive metabolizers (EMs). RESULTS: Data from a total of 149 participants were evaluated and the median (range) of MR was 0.25 (0.03-3.01). The polynomial equation obtained in probit analysis gave an antimode for MR of 1.39. Five (3.36%) participants were PMs and 144 (96.64%) were found to be EMs. One participant had reported mild drowsiness 2 h postdose that subsided spontaneously without any intervention. CONCLUSION: The prevalence of CYP2D6 polymorphism in Western Indian population is low (3.36%) and is similar to other populations.