Pharmacokinetics of thiamphenicol in dogs

Objective - To determine pharmacokinetic parameters of thiamphenicol (TAP) after IV and IM administration in dogs. Animals - 6 healthy 2- to 3- year-old male Beagles. Procedure - In a crossover design study, 3 dogs were given TAP IV, and 3 dogs were given TAP IM, each at a dosage of 40 mg/kg of body weight. Three weeks later, the same dogs were given a second dose by the opposite route. At preestablished times after TAP administration, blood samples were collected through a catheter placed in the cephalic vein, and TAP concentration was determined by use of a high-performance liquid chromatography. Results - Kinetics of TAP administered IV were fitted by a biexponential equation with a rapid first disposition phase followed by a slower disposition phase. Elimination half-life was short (1.7 ± 0.3 hours), volume of distribution at steady state was 0.66 ± 0.05 L/kg, and plasma clearance was 5.3 ≠ 0.7 ml/min/kg. After IM administration, absorption was rapid. Peak plasma concentration (25.1 ± 10.3 μg/ml) was reached about 45 minutes after drug administration. The apparent elimination half-life after IM administration (5.6 ± 4.6 hours) was longer than that after IV administration probably because of the slow absorption rate from the muscle. Mean bioavailability after IM administration was 96 ± 7%. Conclusion - The pharmacokinetic profile of TAP in dogs suggests that it may be therapeutically useful against susceptible microorganisms involved in the most common infections in dogs, such as tracheobronchitis, enterocolitis, mastitis, and urinary tract infections.