Pharmacokinetics of ampicillin and methoxymethyl ester of hetacillin in dogs

Concentrations of ampicillin and the methoxymethyl ester of hetacillin were measured in plasma, prostatic fluid, and spinal fluid of dogs receiving ampicillin or the hetacillin ester by continuous intravenous infusion. The ratios of ampicillin in prostatic fluid relative to plasma levels were higher after dosing with the hetacillin ester. Pharmacokinetic parameter values were consistent with urinary excretion characteristics. Ready diffusion of the ester across biological membranes may facilitate eradication of pathogenic organisms in prostatic and spinal fluids.