Pharmacokinetics of amoxicillin and milk passage during lactation in goats

Abstract

The aims of the present study were to describe the pharmacokinetic profile and milk concentrations of a slow release formulation of amoxicillin administered intramuscularly in goats at different times of lactation, and to determine the PK/PD ratio value. Five healthy lactating goats in their third lactation at 25-30 (peak milk yield) and 150–155 (end of lactation) days postpartum were used. At each experience 20 mg/kg intramuscular amoxicillin was administered. Blood and milk samples were collected at predetermined time and drug concentrations were determined by microbiological assay. In both periods plasma pharmacokinetic parameters were calculated using compartimental analysis. The pharmacokinetic profile was similar in both lactation moments. No differences were detected in the pharmacokinetic parameters or PK/PD values between treatments. Amoxicillin concentrations were not detected in milk. Our results suggest that, based on sensitivity test results, the dose used in this study could be administered every 48 hours, at both times studied for the treatment of infections caused by sensitive microorganisms with MIC ≤ 0.188 μg/mL. For less sensitive bacteria (MIC ≤ 0.25 μg/mL) the dosing interval should be longer during the peak milk yield (48 hours) than at the end of the lactation (22 hours). For microorganisms with MIC ≥ 0.5 μg/mL the serum concentrations achieved show that this formulation should not be used as a depot formulation.