Comparative bioavailability study of two oral formulations of amoxicillin-clavulanic acid in healthy dogs.

Background: Amoxicillin-clavulanic acid combination (AMX-CA) is a widely used oral antibiotic for companion animals. In Thailand, various AMX-CA formulations are available. This study aimed to evaluate and compare the pharmacokinetic profiles and relative bioavailability of two AMX-CA formulations using a randomized, two-period, two-treatment crossover design in six healthy Beagle dogs. Each dog received a 250 mg AMX-CA tablet (formulation A or B) at a dosage of 20.5 ± 2.5 mg/kg, with a 7-day washout period between treatments. Blood samples were collected over a 24-h period post-administration, then AMX and CA concentrations were measured using LC-MS/MS. Bioequivalence was assessed based on the 90% confidence intervals (CI) for peak plasma concentration (Cmax) and the area under the plasma concentration-time curve extrapolated to infinity (AUC0-∞), which required to fall within 80%-125%.

Results: The relative bioavailability of formulation B was 76.5% for AMX and 72.7% for CA, compared to formulation A. Only CA's Cmax met the bioequivalence criteria, while the CIs for AUC0-∞ and Cmax of AMX and AUC0-∞ of CA were outside the acceptable range.

Conclusions: Bioequivalence between the two formulations was not established, indicating that these formulations are not interchangeable.