STUDIES ON PLASMA DISPOSITION, URINARY-EXCRETION AND DOSAGE REGIMEN OF SULFAMETHAZINE IN CALVES

The present study reports the disposition kinetics of sulfamethazine in calves of two different age groups (62.00 +/- 3.09; 377.0 +/- 18.36 days) following a single intravenous dose (100 mgkg-1). Data could be best described by a two Compartment open model. Distribution of the drug was very fast (t 1/2 q; 0.13 +/- 0.02; 0.20 +/- 0.04 h). The elimination half life of sulfamethazine in both the groups was very long (t 1/2 ; 15.81 +/- 2.64; 17.31 +/- 3.23 h). The values of apparent volume of distribution (Vd(area)) were between 0.53 +/- 0.10 to 0.82 +/- 0.18 L kg.-1 The total body clearance values were found to be 24.74 +/- 4.54 and 30.75 +/- 2.07 ml kg-1 h-1 in the younger and the older calves, respectively. There were no significant differences in the kinetic profile of sulfamethazine between the age groups except the (Vd(area)) value which was significantly lower in the younger calves and difficult to explain. During 24 h post-drug adimnistration, 13.35 +/- 1.43 per cent of the total administered dose of sulfamethazine was excreted unchanged in the urine in the older calves. Based on the disposition kinetic values of sulfamethazine in both the agre gropus, the mean priming and maintenance doses would be 51.65 and 23.65 mg kg-1 body weight to be repeated at 12 h intervals to achieve and maintain plasma levels of greater-than-or-equal-to 50-mu-gml-1.