A comparison of some of the pharmacokinetic parameters of three commercial sulphadiazine/trimethoprim combined preparations given orally to pigs.

Three sulphadiazine/trimethoprim preparations were administered orally during feeding to pigs. Six male and six female pigs were used. Clinically important pharmacokinetic parameters of the two drugs in the three preparations were determined and compared. The plasma concentrations of sulphadiazine and trimethoprim increased rapidly in the pigs followed by a quite rapid decrease from 4 to 12 h after oral administration. The mean values of the absorption half-lives of sulphadiazine and trimethoprim were 0.9-1.6 h and 0.5-0.8 h, respectively. The corresponding values for the elimination half-lives of sulphadiazine and trimethoprim were 3.1-4.3 h and 3.4-6.0 h, respectively. There were no significant differences between the pharmacokinetic parameters of the two compounds in the three preparations with the exception of Tmax for sulphadiazine and t 1/2 beta for trimethoprim. Comparative bioavailability calculations showed no statistically significant differences between sulphadiazine and trimethoprim in the three preparations. The weight increase of the pigs during the experimental period (mean = 37.3-64.9 kg) did not cause differences in the kinetics of the two drugs which could have consequences for the use of the three combined preparations in clinical practice. No unacceptable or antibacterial residues of sulphadiazine or trimethoprim were found in the kidneys of pigs slaughtered at 5, 7 and 10 days after administration.