Objective: To evaluate pharmacokinetics of a high dose of gentamicin administered i.v. or i.m. 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), i.v. and i.m., 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 micrograms/ml (0 hours after injection) and 22.0 +/- 4.9 micrograms/ml (1.31 hours after injection) for the i.v. and i.m. groups, respectively. Area under the curve (AUC) was 116.6 +/- 14.5 and 116.3 +/- 14.6 micrograms.h/ml for the i.v. and i.m. groups, respectively. Elimination half-life for the IV group was 3.0 +/- 2.8 hours. Trough concentrations were < 2 micrograms/ml for > 15 and > 12 hours for the i.v. and i.m. 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 i.v. or i.m. 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.