Tissue concentrations and pharmacokinetics of florfenicol in male veal calves given repeated doses.

The pharmacokinetic disposition of florfenicol was studied in male veal calves given 11 mg of florfenicol/kg of body weight, IV and 11 mg of florfenicol/kg PO every 12 hours for 7 doses. After florfenicol administration IV, the median elimination half-life was 222.8 minutes, whereas the median half-life of the distribution phase was 7.94 minutes. Median body clearance and apparent volume of distribution were 2.87 ml/kg/min and 0.907 L/kg, respectively. After florfenicol administration, PO, there was a wide variation in the calculated half-life, which was attributed to variation in the rate of florfenicol absorption. The half-life was 167.4 to 534.9 minutes after the first oral dose and 190 to 808.8 minutes after the seventh dose. The median bioavailability after the first oral dose was 0.8888. Peak and trough concentrations of florfenicol were increased after subsequent doses were administered, compared with those after the first oral dose. The percentage of protein binding in serum from one adult cow was 22% to 26%. Florfenicol concentrations in tissues and body fluids of male veal calves were studied after the seventh dose of 11 mg of florfenicol/kg. High concentrations of florfenicol were measured in the urine, kidney, and bile. Low concentrations were measured in the brain, CSF, and aqueous humor. Concentrations in all other tissues and fluids studied were similar to the concurrent serum concentration.