Some pharmacokinetic aspects of four sulphonamides and trimethoprim, and their therapeutic efficacy in experimental Escherichia coli infection in poultry.

Pharmacokinetic studies in broilers and layers of different sulphonamides indicate a good absorption and a long elimination half-life (of sulphaquinoxaline, sulphadimidine and to a lesser degree sulphadiazine) resulting in high plasma concentrations during drinking water medication in the recommended therapeutic doses. In contrast drinking water medication with high concentrations of trimethoprim (up to 1,320 mg/liter) resulted in a maximal mean plasma concentration of 1.2 micrograms/ml. Very good therapeutic effects were demonstrated in broilers experimentally infected with a sulphonamide-susceptible E. coli strain when treated with sulphaquinoxaline (200 mg/liter), sulphadimidine sodium (2 gram/liter), sulphachloropyridazine 30 per cent (1 gram/liter) and to a lesser degree sulphadiazine sodium (250 mg/liter). Synergism was demonstrated between trimethoprim and sulphadiazine (1:5). The combination of trimethoprim with sulphaquinoxaline (1:3) did not induce better therapeutic effects than sulphaquinoxaline in proportional doses. However, significant synergism was demonstrated between trimethoprim and both sulphonamides in treatment of experimental infection with sulphonamide-resistant E. coli. No signs resembling sulphonamide intoxication were observed during these studies.