The aim of this study was to explore the bioequivalence of long-acting oxytetracycline in two formulations, a reference formulation (Terramycin 20% LA, Pfizer) and a test one (Kangtekang 20% LA, Huishen). Both formulations were administered intramuscularly at 20 mg/kg body weight at each of 24 healthy animals during a two-period crossover parallel experimental design. The oxytetracycline (OTC) concentrations in plasma were measured by high-performance liquid chromatography, and the limit of quantification was 0.05 µg/ml with a recovery ratio of above 90%. Moreover, the descriptive pharmacokinetics parameters (Cmax, AUC0-144h, and AUC0-∞) were calculated and compared under analysis of variance, and 90% confidence interval (CI) were compared, except for Tmax analyzed by non-parametric tests based on Wilcoxons's signed rank test. The comparison results of Cmax, AUC0-144h, AUC0-∞, and Tmax were 5.066 ± 0.486, 5.071 ± 0.877 µg/ml, 118.926 ± 13.259, 126.179 ± 17.390 µg h/ml, 123.087 ± 13.906, 130.732 ± 18.562 µg h/ml, 0.740 ± 0.278, 0.650 ± 0.258 h, respectively, and did not reveal any significant differences. In addition, 90% CIs of these ratios for reference and test product were within an interval of 80-125%, and the relative bioavailability of test one was (94.291 ± 15.287)%. Therefore, it has been concluded that test OTC was bioequivalent to the reference formulation in pigs.
Keywords: bioequivalence; confidence interval; formulations; oxytetracycline; pharmacokinetics.