Pharmacokinetics of Amoxicillin in the Cat

The pharmacokinetics and plasma protein binding of amoxicillin in cats has not been thoroughly investigated. In a single-group sequential designed experimental study, amoxicillin was administered to six healthy cats intravenously, orally, and subcutaneously. Repeated blood samples were drawn after each administration, and amoxicillin concentrations were determined using High Performance Liquid Chromatography coupled to Triple Quadrupole Mass Spectrometry. Plasma amoxicillin data were subjected to population pharmacokinetic analysis, and pharmacokinetic parameters were estimated. The population clearance was 0.18 L/h∙kg, the volume of the central compartment was 0.12 L/kg, the highly perfused compartment was 0.009 L/kg, and the poorly perfused compartment was 0.002 L/kg. The bioavailability was 33% and 69% after oral and subcutaneous administration, respectively. After subcutaneous administration of a slow-release formulation, there was absorption rate-limited pharmacokinetics. The plasma protein binding was 0%-24%. The results increase the understanding of the amoxicillin pharmacokinetics in cats. Further studies combining the results with pharmacodynamic data and in silico simulations are warranted.