Pharmacokinetics and bioequivalence testing of generic ondansetron preparations in healthy Thai male volunteers

Subjects, material and methods: Pharmacokinetics and bioequivalence of oral preparations of generic ondansetron were investigated in healthy Thai males. The test preparations were Vomitron 8 and Vomitron 4, the reference was Zofran. The three products were administered as an 8 mg single oral dose, in a three-period four-sequence crossover design with one-week washout period. An intravenous 8 mg Zofran was administered on the forth visit. Plasma ondansetron concentrations were determined by HPLC and the pharmacokinetic parameters were analyzed by non-compartmental analysis. Results: Following i.v. ondansetron, the mean values of its elimination half-life, its plasma clearance, and its volume of distribution were 4.5 hours, 398 ml/min, and 130 liters, respectively. Its oral bioavailability averaged 67%, and the elimination half-life after oral administration was 5.6 hours. The time to reach the maximal concentration (T-max, hour) of Zofran (1.21 +/- 0.26) was statistically faster than that of Vomitron 8 (1.33 +/- 0.54) and Vomitron 4 (1.46 +/- 0.50). The 90% confidence intervals of the AUC(0-)infinity and C-max ratios mu(T)/mu(R) for (Vomitron 8/Zofran) were 0.88 - 1.12 and 0.85 - 1.08, respectively. Similarly the 90% CI of the AUC(0-)infinity and C-max ratios for (Vomitron 4/Zofran) were 0.96 - 1.17 and 1.01 - 1.19, respectively. Conclusion: These values were within the acceptable range of 0.80 - 1.25, thus our study demonstrated the bioequivalence of Vomitron and Zofran with respect to the rate (C-max) and extent of absorption (AUC(0-)infinity).