PLASMA-CONCENTRATION, TISSUE-CONCENTRATIO N AND URINE-CONCENTRATION OF SULFADIAZINE AND TRIMETHROPRIM AFTER ORAL-ADMINISTRATION OF A FIXED COMBINATION (TABLETS) TO DOGS

The pharmacokinetic of a fixed trimethoprim/sulfadiazine combination w as studied in dogs. Over seven days, the drug was administered orally (dosage: 2.5 and 12.5 mg/kg as well as 7.5 and 37.5 mg/kg trimethoprim and sulfadiazine every 12 hours). After administration of 12.5 mg/kg sulfadiazine, the minimum plasma concentration was higher than 2.8 mu g/ml for sulfadiazine. A plasma level higher than 0.1 mu g/ml was not measurable after repeated administration of 2.5 mg/kg trimethoprim. By repeated treatment with the threefold dose, plasma levels of more tha n 8 mu g/ml sulfadiazine and 0.4 mu g/ml trimethoprim were measured. B ecause of the nearly lacking synergistic effect of trimethoprim and su lfadiazine after administration of 2.5 and 12.5 mg/kg (every 12 hours) , the trimethoprim/sulfadiazine ratio has to be verified for all fixed trimethoprim/sulfadiazine combinations which are destinated for the t reatment of animals. Species differences of pharmacokinetics have to b e considered.