Single intravenous and multiple dose pharmacokinetics of gentamicin in healthy llamas

To determine the pharmacokinetics of gentamicin sulfate in healthy llamas after i.v. administration of a single bolus and after repeated parenteral administration.

Prospective clinical trial.

19 clinically normal, adult male llamas for the single-dose trial and 10 of the 19 llamas for the multiple-dose trial.

In the first trial, llamas were given gentamicin (5 mg/kg of body weight, i.v.) as a single bolus, and serum gentamicin concentration was monitored over the next 48 hours. 2 months later, llamas were given gentamicin (2.5 mg/kg) i.v. for the first day, then IM every 8 hours for 7 days. Serum gentamicin concentration and indices of renal function and damage were monitored during the 7 days.

There were no significant dose- or time-related differences in clearance of the drug; volume of distribution; apparent coefficients of the distribution and elimination phases, alpha and beta, respectively; mean residence time; or distribution (t1/2 alpha) and elimination phase (t1/2 beta) half-lives. The 5 mg/kg i.v. kinetic study revealed t1/2 alpha of 14.5 +/- 5.06 minutes and t1/2 beta of 166 +/- 20.5 minutes. The 2.5 mg/kg i.v. kinetic study revealed t1/2 alpha of 17.7 +/- 6.59 minutes and t1/2 beta of 165 +/- 40.3 minutes. Peak serum gentamicin concentration averaged 10.10 micrograms/ml in the multiple-dose trial, and trough concentration averaged 1.50 micrograms/ml.

Dose effects were not observed for gentamicin clearance, volume of distribution, or half-lives. Multiple dosing at 2.5 mg/kg every 8 hours does not appear to cause renal impairment in healthy llamas.

Gentamicin pharmacokinetic variables in llamas appear to resemble those in other ruminant species.