Bioequivalence Study of Warfarin in Healthy Chinese Volunteers With a Validated High-Performance Liquid Chromatography-Mass Spectrometry Method

A physiologically based pharmacokinetic/pharmacodynamic modeling approach for drug-drug interaction evaluation of warfarin enantiomers with sorafenib

Sorafenib was suggested to cause drug-drug interaction (DDI) with the common anticoagulant, warfarin based on published studies. The inhibition on CYP2C9 enzyme was thought to be the mechanism, but further studies are warranted. Thus, a mechanistic PBPK/PD model for warfarin enantiomers was developed to predict DDI potential with sorafenib, aiming at providing reference for the rational use of both drugs. PBPK models of warfarin enantiomers were constructed by Simcyp software. A mechanistic PK/PD model was built in NONMEM software. PBPK model of sorafenib was fitted via a top-down method. The final PBPK/PD model of warfarin enantiomers was verified and validated by different dosing regimens, ethnicities and genetic polymorphisms, and used to perform DDI simulations between warfarin racemate and sorafenib among general populations and sub-populations with various CYP2C9 and VKORC1 genotypes. Results suggested low DDI risk between warfarin and sorafenib for general populations. Potentially serious consequence was seen for those carrying both CYP2C9 ∗2 and ∗3 and VKORC1 A/A genotypes. This PBPK/PD modeling approach for warfarin enantiomers enabled DDI evaluation with sorafenib. Close monitoring and warfarin dosage adjustment were recommended for patients carrying mutant genotypes. The novel model could be applied to investigate other drugs that may interact with warfarin.

A Two-Sequence, Four-Period, Crossover, Replicate Study to Demonstrate Bioequivalence of Warfarin Sodium Tablet in Healthy Chinese Subjects Under Fasting and Fed Conditions

Warfarin is a narrow therapeutic index anticoagulant drug, and several generic formulations have been approved worldwide. However, there has been no report evaluating the bioequivalence of warfarin sodium according to US Food and Drug Administration draft guidance. We designed a 2-sequence and 4-period crossover study to compare the pharmacokinetic profile and assess bioequivalence between the test warfarin sodium tablet and reference product Coumadin (2.5 mg) in 56 healthy Chinese subjects under fasting and fed conditions. The plasma concentration of warfarin was analyzed by a validated liquid chromatography-tandem mass spectrometry assay, and the reference-scaled procedure was used to determine bioequivalence for the pharmacokinetics parameters. The results showed that the point estimate of geometric mean ratios of C_max and AUC_0-t for warfarin were 103.21% and 99.31%, respectively, in the fasting condition and 100.62% and 98.98%, respectively, in the fed condition, and the 90% confidence intervals were all within the range of 90.00%-111.11%. The upper limit of the 90% confidence interval of estimated within-subject variation ratios of the test and reference products was 1.33 for C_max and 2.22 for AUC_0-t under the fasting condition and 1.68 for C_max and 2.15 for AUC_0-t under the fed condition. Overall, bioequivalence of the 2 warfarin sodium products was demonstrated.