Pharmacokinetics in the calf of a long-acting chloramphenicol formulation administered intravenously and intramuscularly.

In a preliminary study, 3 different chloramphenicol doses were tested by intramuscular (im) route, the highest one (90 mg/kg) being selected, based upon the duration of therapeutic serum levels (41.7 h). Following intravenous (iv) administration at this dose rate, the main pharmacokinetic parameters were: half-life of 6.0 h; body clearance, 0.101 l.kg-1.h-1; steady-state volume of distribution, 0.864 l.kg-1. Following a single im administration at the same dose, a mean maximum serum concentration of 22.9 microgram.ml-1 (Cmax) was reached in a mean time of 8.9 h (Tmax), therapeutic serum levels were achieved in an average period of 41.3 h. The mean half-life of the terminal phase was 10.3 h. Absolute bioavailability calculated based on 3 calves was 70.9 +/- 23.3% by im route. Pharmacokinetics of the long-acting formulation were confirmed in a repeated-dose study using the dosage schedule selected (2 injections im of 90 mg/kg at a 48 h interval).