Conducting bioequivalence studies is an essential step during the market authorization process of generic pharmaceutical formulations, for both human or veterinary use. The aim of the present study was to evaluate the pharmacokinetics of triclabendazole sulphoxide, the main metabolite of triclabendazole, and ivermectin in order to evaluate the bioavailability and bioequivalence of a novel sheep anthelmintic formulation of oral suspension for sheep treatment containing triclabendazole 50 mg/mL and ivermectin 1 mg/mL compared to the reference product. In order to determine relative bioavailability of the test product with respect to the reference product the study was conducted on 36 clinically healthy sheep, following an unicentric, randomized, cross-over, two-sequence, two-treatment and 14-day wash-out study design. For the determination of triclabendazole sulphoxide and ivermectin sheep plasma concentrations, two rapid, selective high performance liquid chromatography coupled with mass spectrometry (LC-MS/MS) methods were developed and validated. The measured plasma concentrations of triclabendazole sulphoxide and ivermectin were used for the pharmacokinetic analysis and the determination of bioequivalence between the test product with regards to the reference product. The noncompartmental analysis of the pharmacokinetic data for both triclabendazole sulphoxide and ivermectin showed similarities between first-order kinetics of the test and reference product. The relevant pharmacokinetic parameters (Cmax, AUClast, AUCtot) were determined and the bioequivalence between the test and reference product could be concluded.
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