Duloxetine 60 mg twice daily is a moderately potent CYP2D6 inhibitor, intermediate between paroxetine and sertraline. The potent CYP2D6 inhibitor paroxetine has a moderate effect on duloxetine concentrations. The results of these 2 studies suggest that caution should be used when CYP2D6 substrates and inhibitors are coadministered with duloxetine.

What is already known about this subject • Atomoxetine is a cytochrome P450 2D6 (CYP2D6) substrate and its pharmacokinetics has been characterized in a predominantly White population during clinical development. • There are scant East Asian pharmacokinetic data available. • The CYP2D6*10 allele is particularly prevalent in East Asian populations and may contribute to the known ethnic differences in CYP2D6 metabolic capacity. What this study adds • The pharmacokinetics of multiple‐dose 80 mg daily atomoxetine observed in Chinese healthy subjects appears comparable to previous data in other ethnic populations. • Homozygous CYP2D6*10 subjects appear to have higher exposures, but are not a clearly distinct group compared with other CYP2D6 extensive metabolizers. Aims To characterize atomoxetine pharmacokinetics, explore the effect of the homozygous CYP2D6*10 genotype on atomoxetine pharmacokinetics and evaluate the tolerability of atomoxetine, in healthy Chinese subjects. Methods Twenty‐four subjects, all CYP2D6 extensive metabolizers (EM), were randomized to receive atomoxetine (40 mg qd for 3 days, then 80 mg qd for 7 days) or matching placebo (2 : 1 ratio) in a double‐blind fashion. Atomoxetine serum concentrations were measured following single (40 mg) and multiple (80 mg) doses. Adverse events, clinical safety laboratory data and vital signs were assessed during the study. Results Atomoxetine was rapidly absorbed with median time to maximum serum concentrations of approximately 1.5 h after single and multiple doses. Atomoxetine concentrations appeared to decrease monoexponentially with a mean apparent terminal half‐life (t1/2) of approximately 4 h. The apparent clearance, apparent volume of distribution and t1/2 following single and multiple doses were similar, suggesting linear pharmacokinetics with respect to time. Homozygous CYP2D6*10 subjects had 50% lower clearances compared with other EM subjects, resulting in twofold higher mean exposures. No clinically significant changes or abnormalities were noted in laboratory data and vital signs. Conclusions The pharmacokinetics of atomoxetine in healthy Chinese subjects appears comparable to other ethnic populations. Multiple dosing of 80 mg qd atomoxetine was well tolerated in this study.

What is already known about this subject• The pharmacokinetics of duloxetine have been assessed in a number of clinical studies.• Duloxetine is eliminated through oxidative metabolism via CYP1A2 and, to a lesser degree, CYP2D6.• There is strong evidence that the prevalence of CYP2D6 phenotypes and the activity of CYP1A2 enzyme activity differ between Japanese and Caucasians.• Given the characteristics of duloxetine metabolism, there is good reason to assess pharmacokinetic differences between Japanese and Caucasians. What this study adds• Duloxetine pharmacokinetics in Japanese or Caucasian subjects is not meaningfully different after single or multiple doses of duloxetine.• The magnitude of pharmacokinetic differences between groups is small relative to the pharmacokinetic variability in either group, and these small differences can be accounted for by differences in body weight.• The result of this study suggests that different dose recommendations for Caucasian or Japanese patients are not likely to be necessary. AimsTo compare single-and multiple-dose duloxetine pharmacokinetics between healthy Japanese and Caucasians. MethodsTwenty-four subjects of each race were given single oral doses of duloxetine (20, 40 and 60 mg) in a randomized, double-blind study. Another 20 subjects of each race received 20, 40 mg or placebo (2 : 2 : 1) twice-daily for 5 days. ResultsFollowing single doses, the mean duloxetine C max and AUC were approximately 20% greater in Japanese. This difference could be explained by the 15% lower average body weight in Japanese. Similar results were observed following multiple dosing. ConclusionDuloxetine pharmacokinetics are not meaningfully different between Japanese and Caucasians. Racial comparison of duloxetine pharmacokineticsBr J Clin Pharmacol 63 :3 311