PHARMACOKINETICS AND THERAPEUTIC POTENTIAL FOR REPEATED ORAL DOSES OFTRIMETHOPRIM SULPHACHLORPYRIDAZINE IN HORSES/

The pharmacokinetic parameters of a powder formulation of trimethoprim /sulphachlorpyridazine were studied in eight healthy horses which rece ived 5 mg/kg trimethoprim and 25 mg/kg sulphachlorpyridazine 12-hourly with concentrate for five days. The intake of the medicated concentra te by the horses was variable during the first two days, but after the y became accustomed to the taste the intake by all the horses during t he last three days was good. Faecal samples taken before and on the la st day of the drug administrations were negative when cultured for sal monella. Compared with the results of a previous single-dose experimen t, higher plasma concentrations and a higher area under the curve for both the drugs were observed. The repeated doses provided plasma conce ntrations above the minimal inhibitory concentration for Streptococcus zooepidemicus, S equi, Actinobacillus equuli and Rhodococcus equi iso lated from the respiratory tract of horses. Synergism between the two drugs occurred at different drug concentration ratios with different b acterial species.