Objective:In vitro information on dextromethorphan (DXM) and the Advanced Dissolution Absorption Metabolism (ADAM) model, incorporated into PBPK simulator Simcyp(@) (v.12) were used to investigate differences in the pharmacokinetics of dextromethorphan between CYP2D6 extensive metabolizers (EM) and intermediate metabolizers (IM).Information on genetic variation of CYP2D6 was integrated to assess the power of studies to detect differences between EMs and IMs.Method:In vitro information on DXM was taken from Simcyp library and literature research.In vitro drug release data of commonly used sustained release formulation was embedded in ADAM model.Target subjects are Chinese healthy volunteers and sub-groups are CYP2D6 EM and IM populations separately.Observed data are from 21 healthy Chinese subjects, 30mg dextromethorphan, oral administration and sustained release tablet.Results:The comparisons between simulation and observation in EM and IM groups separately are quite good.Based on the simulation results, power analysis can be done by calculating powers in the cases of different sample sizes.Eventually, a power curve shows thatat least 18 subjects (9 for EM and IM group separately) are needed to make sure that the power is above 80%.Conclusion:At least 18 subjects (9 for EM and IM group separately) are needed to make sure that the power is above 80%.PBPK model and clinical trial simulation are the new way to do power analysis.