Bioequivalence evaluation of two D-limonene capsule formulations in healthy Chinese volunteers.

A randomized, three-period crossover study was conducted in 24 healthy Chinese male volunteers to compare the bioavailability of two brands of D-limonene (0.3 ml) capsules, and determine the plasma concentration of endogenous D-limonene in food-controlled non-treated humans. The three kinds of treatments were administration of the reference formulation, administration of the test, and non-administration. The plasma samples were analyzed by a validated GC-MS method after liquid-liquid extraction. The pharmacokinetic parameters AUC(0-t), AUC(0-infinity), Cmax, tmax, and t1/2 were determined from the concentration-time profiles for both formulations and were compared statistically to evaluate bioequivalence between the two brands. The analysis of variance (ANOVA) did not show any significant difference between the two formulations and 90% confidence intervals fell within an acceptable range for bioequivalence. Besides, for the food-controlled non-treated volunteers, their plasma concentrations of D-limonene were detectable and kept relatively steady (2.94 +/- 1.38 ng/ml) within the sample collection period. Based on the statistical analysis, it was concluded that the two D-limonene capsule formulations were bioequivalent.