The pharmacokinetic properties of amoxicillin (AMX) and clavulanic acid (CLV) were studied in healthy cats following single intravenous and oral dosage of 10 mg/kg of AMX and 2.5 mg/kg of CLV. The drug concentrations in plasma were determined by a high‐performance liquid chromatographic–tandem mass spectrometry (LC‐MS‐MS) method validated for canine plasma and further subjected to noncompartmental analysis. After intravenous injection, no significant difference (p > 0.05) was found in the volume of distribution of these two compounds. In addition, AMX and CLV were both rapidly eliminated from plasma with a clearance of 0.453 and 0.921 L hr−1 kg−1, respectively; however, a quicker elimination was observed for CLV (p < 0.01). After oral administration, both drugs were characterized by rapid absorption with an absorption half‐life of 1.10 and 0.70 hr for AMX and CLV, respectively. Significant differences were observed between their absorption rates (p < 0.05). However, the oral bioavailabilities of AMX and CLV (75.57% and 98.15%, respectively) were not statistically different (p > 0.05). A total intravenous or oral dose at 12.5 mg/kg of AMX and CLV (4:1) is predicted to be effective for treating those bacterial species isolated from cats with a minimum inhibitory concentration (MIC) of ≤0.25 μg/ml for 12 hr, based on a time above the MIC (T > MIC) of 40%.

A rapid, sensitive, and specific high-performance liquid chromatography tandem mass spectrometric method was developed for the simultaneous determination and confirmation of amoxicillin and clavulanic acid in plasma. Plasma sample was subjected to a simple deproteinization with acetonitrile, and then the supernatant was directly diluted by water. Analysis was performed on a Phenomenex Luna C 8 reversed-phase column by detection with mass spectrometry in negative ions multiple reaction monitoring mode. A gradient elution program with 0.1% formic acid and acetonitrile was performed at a flow of 0.25 mL min À1 . There is good linearity in the range of 0.5-500 ng mL À1 for both amoxicillin and clavulanic acid. The decision limits of amoxicillin and clavulanic acid were 0.06 ng mL À1 and 0.08 ng mL À1 in plasma, respectively, and the detection capabilities of two analytes were below 0.5 ng mL À1 . Acceptable precision and accuracy were obtained for concentrations over the standard curve range. The extraction recoveries of amoxicillin and clavulanic acid were between 102% and 115% in plasma at three spiked levels of 0.5, 50, and 500 ng mL À1 , with the relative standard deviations less than 15% for each analyte. The developed method was applied to pharmacokinetic studies of amoxicillin and clavulanic acid tablets in healthy beagles.