Pharmacokinetics of florfenicol after intravenous and intramuscular dosing in llamas

Florfenicol, is a broad spectrum antimicrobial agent with wide tissue distribution commonly used to treat camelids. To address the lack of drug disposition data for florfenicol in llamas, we evaluated the pharmacokinetics after 20mg/kg intravenous (i.v.) and intramuscular (i.m.) dosing. Serum concentrations were determined using a HPLC-UV assay and pharmacokinetic analysis was conducted using non-compartmental analysis. Following i.v. injection, systemic clearance and Vdss in llamas were 4.6mL/min/kg and 737mL/kg, respectively. Mean residence time after i.v. dosing was 3h. After i.m. injection, florfenicol was rapidly absorbed, with Cmax concentrations being 3.2μg/mL at 0.5h, mean residence time was 15h, mean absorption time was 12h and absolute bioavailability of florfenicol after i.m. injection was 63%. The prolonged absorption of florfenicol after i.m. administration suggests the apparent HL_λz reflects the absorption process rather than elimination of the drug. Florfenicol administration was not associated with adverse reactions after dosing by either route. Serum florfenicol concentrations remained >1.0μg/mL for 12h after i.m. administration. For susceptible pathogens, once daily dosing of 20mg/kg body weight appears appropriate.