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

Abstract

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 μg/ml (0 hours after injection) and 22.0 ± 4.9 μg/ml (1.31 hours after injection) and 22.0 ± 4.9 μg/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 μg·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 μg/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, AUC, 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.