ORAL BIOAVAILABILITY OF SULPHAMETHOXYDIAZINE, SULFATHIAZOLE AND SULPHAMOXOLE IN DWARF GOATS

To get a better insight into the oral bioavailability of sulphonamides in ruminants, sulphamethoxydiazine (pKa 7.0), sulphathiazole (pKa 7.2 ), and sulphamoxole (pKa 7.4) were administered to dwarf goats (n=5). The drugs were given at 2-week intervals by the intravenous or intraru minal route at a dose of 100 mg per kg body weight. After IV injection , the mean half-life ( t1/2beta in h +/- SEM) was 0.80 +/- 0.10 h, 2.3 5 +/- 0.38 h, and 3.36 +/- 1.25 h, for sulphathiazole, sulphamoxole, a nd sulphamethoxydiazine, respectively and the mean distribution volume (V(dbeta)) was 0.23 +/- 0.05 l/kg, 0.23 +/- 0.04 1/kg, and 0.33 +/- 0 .02 l/kg. After intraruminal administration, the mean bioavailability varied from 86.0 +/- 11.8 % for sulphamethoxydiazine to 46.6 +/- 4.3 % for sulphamoxole, and 52.6 +/- 7.2 % for sulphathiazole. The eliminat ion half-life was significantly prolonged, probably due to a low rate of drug absorption from the gastrointestinal tract. In contrast to chl oramphenicol, the sulphonamides studied were stable when incubated in rumen fluid at 39-degrees-C.