Original Manuscript Clinical Pharmacology in Drug Development 2017, 00(0) 1–7 C  2017, The American College of Clinical Pharmacology DOI: 10.1002/cpdd.348 Bioequivalence Study of Warfarin in Healthy Chinese Volunteers With a Validated High-Performance Liquid Chromatography-Mass Spectrometry Method Wenlong Li * , Fanlong Bu * , Rong Li, Benjie Wang, Abdul Sami Shaikh, Yunyun Zhang, Ruichen Guo, and Rui Zhang Abstract This study was designed to investigate the pharmacokinetics of an innovative flm-coated warfarin sodium tablet and to compare it with the marketed sugar-coated warfarin sodium tablet in humans. A single-dose, open-label, randomized, two-way crossover study was performed in 24 healthy Chinese male volunteers.They were administered 2.5 mg of innovative flm-coated warfarin sodium tablets or the marketed sugar-coated warfarin sodium tablets. Blood samples were collected at different time points after dosing for investigation of the pharmacokinetics of warfarin in human plasma. A sensitive liquid chromatography mass spectrometry method was established to determine warfarin in plasma.Drug and Statistics 2.1.1 was applied to calculate the pharmacokinetics parameters. The main pharmacokinetic parameters for flm- coated and sugar-coated warfarin were the following: t ½ , 103.5 ± 18.8 and 105.8 ± 21.3 hours; T max , 0.7 ± 0.5 and 1.3 ± 0.8 hours; C max , 347.8 ± 74.8 and 322.9 ± 75.7 ng/mL; AUC 0360 , 16,024.2 ± 3713.9 and 15,586.6 ± 3477.0 ng·mL −1 ·h; AUC 0 , 17,335.7 ± 4089.1 and 16,912.0 ± 3911.2 ng·mL −1 ·h, respectively. The human pharmacokinetics of flm- coated and sugar-coated warfarin were slightly different.The oral absorption and bioavailability of innovative flm-coated warfarin were slightly higher than those of the sugar-coated warfarin. This study is vital to clinical usage of warfarin not only because of the pharmacokinetic parameters of the 2 pharmaceutical dosage forms of warfarin but also to obtain data on the prevalence of CYP2C9 and VKORC1 genes and their infuence on the concentration of warfarin. Keywords warfarin, pharmacokinetics, bioequivalence, gene polymorphism, HPLC-MS Warfarin is an oral anticoagulant of the coumarin class (Figure S1). It is widely used as an oral anticoagulant in the treatment of deep venous thrombosis, pulmonary embolus, valvular replacement, atrial fbrillation, and the prevention of myocardial infarction. 1 Warfarin is completely absorbed after oral admin- istration and then is highly bound to albumin in the plasma. An inverse relationship between the albumin and free warfarin levels is 1 reason why postoperative or severely ill patients require lower doses of warfarin. 2,3 It is well known that the pharmaceutical dosage form is an important factor infuencing the phar- macokinetics and bioavailability of drugs. 4 The in- novative flm-coated warfarin sodium tablet and the currently marketed sugar-coated warfarin sodium tablet have different coating materials, which may have an infuence on the pharmacokinetics of warfarin. Compared to the marketed sugar-coated tablets, the innovative flm-coated tablets have many advantages such as a shorter production cycle, fewer adverse reac- tions, and a larger range of applications. It is reported that analytes of warfarin were identifed and qualifed by high-performance liquid chromatography (HPLC) 5 Institute of Clinical Pharmacology, Qilu Hospital of Shandong University, Jinan, Shandong Province, China 250012 Submitted for publication 2 January 2017; accepted 16 February 2017. Corresponding Author: Rui Zhang, Institute of Clinical Pharmacology, Qilu Hospital of Shandong University, Jinan, Shandong Province, China 250012 (e-mail: grc7636@126.com) ∗ Co-frst authors.