Pharmacokinetics of florfenicol in North American elk (Cervus elaphus)

Florfenicol pharmacokinetics after administration of a single subcutaneous (s.c.) dose of 40 mg/kg of body weight in adult elk (Cervus elaphus) was investigated. Serum florfenicol concentrations were determined by a sensitive high-performance liquid chromatographic method with limit of quantification of 0.03 mug/mL. Florfenicol pharmacokinetic parameters in elk were estimated using a noncompartmental approach. After a single s.c. injection, florfenicol concentrations remained above 1 mug/mL for approximately 36 h and above 0.5 mug/mL for approximately 72 h. Following s.c. injection, florfenicol was absorbed rapidly with a mean maximum concentration (C-max) of 3.7 mug/mL achieved at 4.2 h (T-max). The C-max value in elk is similar to values reported in cattle at the same dose, suggesting that the 40 mg/kg s.c. dose achieves therapeutic concentrations in elk. A mean elimination half-life (t(1/2)) of 44 h is shorter than that reported in cattle. The more rapid elimination half-life in elk suggests that elk may require a multiple dose regimen for therapeutic success with s.c. Nuflor(R). We recommend s.c. Nuflor(R) be administered subcutaneously to elk every 24 h at a dose level of 40 mg/kg.