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.