THE PHARMACOKINETICS OF THIAMPHENICOL IN LACTATING COWS

The pharmacokinetics of thiamphenicol were studied after intravenous a nd intramuscular administration of 25 mg/kg body weight in lactating c ows. Distribution (T1/2alpha) and elimination (t1/2beta) half-lives of 6.10 +/- 1.39 min and 1.60 +/- 0.30 h, respectively, were obtained af ter intravenous administration. The body clearance was 3.9 +/- 0.077 m l/kg per min and the apparent volume of distribution was 1220.79 +/- 2 56.67 ml/kg. The rate at which thiamphenicol appeared in the milk, as indicated by the penetration half-life (t1/2P) (serum to quarters), wa s found to be 36.89 +/- 11.14 min. The equivalent elimination half-lif e (t1/2E) (quarters to serum) from the milk was 3.62 +/- 1.06 h and th e peak thiamphenicol concentration in the milk was 23.09 +/- 3.42 mug/ ml at 2.5 +/- 0.32 h. After intramuscular injection, the elimination h alf-life was 2.2 +/- 0.40 h, the absorption half-life was 4.02 +/- 1-7 2 min and the peak concentration in the serum was 30.90 +/- 5.24 mug/m l at 23 +/- 8.4 min. The bioavailability after intramuscular administr ation approached 100%. The penetration half-life was 50.59 +/- 6.87 mi n, the elimination half-life was 5.91 +/- 4.97 h and the mean peak con centration in the milk was 17.37 +/- 2.20 mug/ml at 3.4 +/- 0.22 h.