A randomized, open-label, 2-period, crossover bioequivalence study of two oral formulations of 75 mg oseltamivir in healthy Thai volunteers

Aim: Oseltamivir, an ester prodrug of its active carboxylate metabolite, is an effective neuraminidase inhibitor used to treat influenza A and B virus infections. The purpose of this study was to compare the bioavailability of two 75 mg oral formulations of oseltamivir: a generic drug, GOP-A-Flu™ (test, Government Pharmaceutical Organization, Thailand) and Tamiflu® (reference, Hoffmann-La Roche Ltd., Nutley, NJ, USA) in healthy volunteers. Subjects and methods: A single-dose, randomized, 2-sequence, crossover study was conducted in 24 healthy Thai volunteers. Each volunteer received a 75 mg capsule of the reference or test drugs under fasting conditions. Blood samples were collected before dosing and at various time points up to 48 hours after dosing and analyzed for plasma oseltamivir and oseltamivir carboxylate concentrations. The pharmacokinetic parameters including C max , AUC 0-t , AUC 0-∞ t max and t 1/2 were analyzed using the non-compartmental method. Drug safety was assessed. Results: 23 volunteers completed both treatment periods. The geometric mean ratios (test/reference) between the two formulations of oseltamivir were 96.83% (90% Cl, 76.85 - 123.15%) for C max 103.66% (86.44-113.56%) for AUC 0.-t , and 103.98% (86.44- 113.56%) for AUC 0-∞ . Those of oseltamivir carboxylate were 102.17% (90% Cl, 90.90 - 109.10%) for C max , 103.95% (90.90 - 109.10%) for AUC 0-t, and 103.95% (90.92 - 109.08%) for AUC 0-∞ . No significant difference of the t max of oseltamivir and oseltamivir carboxylate between the two formulations was detected (p > 0.05). Both formulations were well-tolerated. Conclusion: Although the C max of oseltamivir was the only parameter not entirely within the equivalence criteria, the two capsule formulations were considered bioequivalent in terms of rate and extent of absorption regarding its active carboxylate metabolite.