Pharmacokinetics of a high dose of gentamicin administered intravenously or intramuscularly to horses

Objective-To evaluate pharmacokinetics of a high dose of gentamicin administered IV or IM to horses. Design-Repeated-measures study, Animals-6 clinically normal female adult stock-type horses. Procedure-All horses were given gentamicin (6.6 mg/kg [3 mg/lb] of body weight), IV and IM, in a two-way cross-over design. Serum gentamicin concentrations were measured during a 24-hour period. Results-Plasma concentration curves were consistent with a two-compartment model. Maximum plasma gentamicin concentrations were 71.9 +/- 15.7 mu g/ml (0 hours after injection) and 22.0 +/- 4.9 mu g/ml (1.31 hours after injection) for the IV and IM groups, respectively. Area under the curve (AUC) was 116.6 +/- 14.5 and 116.3 +/- 14.6 mu g . h/ml for the IV and IM groups, respectively. Elimination half-life for the IV group was 3.0 +/- 2.8 hours. Trough concentrations were < 2 mu g/ml for > 15 and > 12 hours for the IV and IM groups, respectively. Significant changes were not detected in clinicopathologic variables before and after administration of gentamicin. Clinical Implications-Administration of a high dose of gentamicin IV or IM resulted in peak plasma concentrations, AUG, and minimum trough plasma concentrations. Results indicate once-daily administration of gentamicin might be as efficacious and safe as multiple-dose daily administration in accordance with traditional low-dose regimens, similar to those used in other species.