[Pharmacokinetics, biological availability and residues of sulfadoxine and trimethoprim when used jointly on calves].

In calves (cross-breds--Bulgarian Brown Cattle breed and Black Spot Cattle bred) weighing about 189 kg pharmacokinetics of sulphadoxine (SD) and trimethoprim (TMP) was studied. The two substances were administered in combination (5 + 1) as a dosage form Tridoxin (Pharmachim, Bulgaria; 24% injectable solution) (TD) at a dose 15 mg/kg m. The results show that after intramuscular administration TD is absorbed relatively rapidly. SD and TMP have systemic availability 94.1 +/- 18.1% and 52.5 +/- 6.2% and produce blood levels, after a single dose of TD, higher than potentiated minimum inhibitory concentrations for 24-48 h and 5(4-8) h, respectively. Upon intravenous administration the two-compartmental model is applicable for the distribution and elimination of SD and TMP (for TMP in part of the animals one-compartmental model is applicable). The two substances are distributed relatively widely in organs and tissues. The biological half-life of TD--t1/2 beta for SD is 14.36 +/- 1.40 h and for TMP--2.40 +/- 0.31 (for one-compartmental model--1.92 +/- 0.26) h, Vd--429.9 +/- 16.9 ml/kg and for TMP in part of the animals one-compartmental model is applicable). The two substances are distributed relatively widely in organs and tissues. The biological half-life of TD--t1/2 beta for SD is 14.36 +/- 1.40 h and for TMP--2.40 +/- 0.31 (for one-compartmental model--1.92 +/- 0.26) h, Vd--429.9 +/- 16.9 ml/kg and for TMP in part of the animals one-compartmental model is applicable). The two substances are distributed relatively widely in organs and tissues. The biological half-life of TD--t1/2 beta for SD is 14.36 +/- 1.40 h and for TMP--2.40 +/- 0.31 (for one-compartmental model--1.92 +/- 0.26) h, Vd--429.9 +/- 16.9 ml/kg and 655.8 +/- 77.6 (for one-compartmental model--671.7 +/- 40.0) ml/kg, ClB--0.35 +/- 0.02 ml/kg/min and 2.87 +/- 0.35 (for one-compartmental model--4.15 +/- 0.80) ml/kg/min, respectively. After intramuscular injection at the dose used a suitable withdrawal time for meat and internal organs is 5 days and for milk--2 days.