en Infectious Diseases Infectious Diseases Original Article Original Article Background: CYP2D6 is polymorphically expressed enzyme that show marked interindividual and interethnic variation. Phenotyping of CYP2D6 provides valuable information about real-time activity of this important drug-metabolizing enzymes through the use of specific probe drugs. The aim of this study was to identify the CYP2D6 oxidation phenotype with dextromethorphan (DEX) as a probe drug in Mazandarani ethnic group among Iranian population. <br>Methods: The study included 71 unrelated healthy volunteers. Dextromethorphan hydrobromide (30 mg) was given orally to healthy subjects and peripheral venous blood samples (10 ml) were taken at 3 hr post-dose. Dextromethorphan and the metabolite dextrorphan (DOR) were analyzed by the HPLC method. The log DEX/DOR metabolic ratio (MR) at 3 hr plasma sample was used as the index of CYP2D6 activity and a value of 0.3 was used as the antimode separating extensive metabolizers (EM) and poor metabolizers (PM) phenotypes. <br>Results: A 560-fold interindividual variation in dextromethorphan MRs was observed in this study. Considering the antimode 0.3 in log scale, 7.04% (5/71) volunteers were identified as PMs.<br>Conclusion: The result showed that the frequency of CYP2D6 PM phenotypes accounted for 7.04% of subjects in our samples. Despite these findings, we propose a further study in larger samples to provide a wider image and to get more valuable information upon pharmacogenetic basis for individual therapy and personalized medicine. Phenotype, Polymorphism, CYP2D6, Dextromethorphan, Mazandaran, Iran 213 217 http://caspjim.com/browse.php?a_code=A-10-62-45&slc_lang=en&sid=1 Shiran Mohammad Reza 1003194753284600393 1003194753284600393 Yes Fatemeh Sarzare 1003194753284600394 1003194753284600394 No Fatemeh Merat 1003194753284600395 1003194753284600395 No Ebrahim Salehifar 1003194753284600396 1003194753284600396 No Ali Akbar Moghadamnia 1003194753284600397 1003194753284600397 No Seyed Mohammad Bagher Hashemi Soteh 1003194753284600398 1003194753284600398 No