A randomized, open-label, two-period, crossover bioavailability study of two oral formulations of tacrolimus in healthy Korean adults

Background: Tacrolimus is a macrolide immunosuppressant used in transplantation. It has been shown to have a comparable therapeutic effect and a low adverse drug reaction profile relative to cyclosporme. Objective: The present study compared the pharmacokinetics of twice-daily doses of 2 tacrolimus formulations used in clinical practice in Korea: a conventional (reference) formulation and a more recently developed (test) formulation. The bioavailability of the 2 formulations was evaluated based on the requirement of 20% deviation at a power of 80%. Methods: This study had a randomized, open-label, 2-period, crossover, noninferiority design. There was a 96-hour treatment period for each formulation, with a 3-week washout period between formulations. Each healthy adult subject received two 1-mg capsules of the reference or test formulation of tacrolimus twice daily (morning and evening), for a total daily dose of 4 mg. Blood samples were obtained during the 96-hour period after the first dose in each treatment period, with tolerability assessments performed up to 2 weeks after the first dose in each period. The primary pharmacokinetic parameters were C_max and AUC from time 0 to the last measured concentration and extrapolated to infinity. Secondary pharmacokinetic parameters were T_max, t_1/2, C_min0-24, AUC_0-24, and C₉₆. Results: The study enrolled 29 healthy Korean volunteers (22 men, 7 women; mean [SD] age, 29 [7] years; age range, 20-51 years; mean weight, 66 [10] kg; mean height, [171 17] cm). All volunteers completed both treatment periods. The 90% Cls for the ratios of the pharmacokinetic parameters (test:reference drug) were 119.25-161.29 for C_max, 95.29-129.04 for AUC_0-t, and 95.63-131.42 for AUC_0-∞. Based on the 80% to 125% bioequivalence criterion, these results indicated that pharmacokinetic exposure to the test drug was not inferior to that of the reference drug. Both formulations were well tolerated, with no serious adverse events reported. Conclusion: In these healthy Korean adults, there were no statistically significant differences between the pharmacokinetic parameters of the more recently developed oral formulation of tacrolimus and the conventional formulation.