Application of a physiologically based pharmacokinetic model for the evaluation of single-point plasma phenotyping method of CYP2D6

Purpose Determining metabolic ratio from single-point plasma is potentially a good phenotyping method of CYP2D6 to reduce the required time interval and increase the reliability of data. It is difficult to conduct large sample size clinical trials to evaluate this phenotyping method for multiple plasma points. A physiologically based pharmacokinetic (PBPK) model can be developed to do simulations based on the large virtual Chinese population and evaluate single-point plasma phenotyping method of CYP2D6. Methods Pharmacokinetic data of dextromethorphan (DM) and its metabolite dextrorphan (DX) after oral administration were used for model development. The SimCYP® model incorporating Chinese demographic, physiological, and enzyme data was used to simulate DM and DX pharmacokinetics in different phenotype groups. Results The ratios of the simulated to the observed mean AUC and Cmax of DM were 1.01 and 0.81 for extensive metabolizers (EMs), 0.90 and 0.81 for intermediate metabolizers (IMs), and 1.12 and 0.84 for poor metabolizers (PMs). The ratios of the simulated to the observed mean AUC and Cmax of DX were 1.12 and 0.89 for EMs, 0.66 and 0.62 for IMs. All ratios were within the predefined criterion of 0.5–2. The simulations of DM and DX pharmacokinetic profiles in 1000 virtual Chinese subjects with reported frequencies of different phenotypes indicated that statistically significant correlations were found between metabolic ratio of DM to DX (MRDM/DX) from AUC and from single-point plasma from 1 to 30 h (all p-values < 0.001). Conclusion MRDM/DX from single-point plasma from 1 to 30 h after the administration of 30 mg controlled-release DM could predict the MRDM/DX from AUC well and could be used as the phenotyping method of CYP2D6 for EMs, IMs, and PMs.