In ruminants, drug absorption from the rumen occurs by passive diffusion of unionized fraction of the drug. Apart from rumen fluid solubility (at pH 6.5). PKa value and lipid solubility. other factors can affect the rate of absorption and drug bioavailability (BA). These factors indude drug absorption to rumen contents and its biodegradation by rumen flora and fauna. Sulfadimidine (SDD) has been the most frequently prescribed sulfonamide in veterinary medicine. However, in dwarf goats SOD oral BA is incomplete (mean value: 26. 4%). Probably as a consequence of a marked “first pass” effect. In the present study, 4 other sulfonamides were investigated: sulfamoxol (S MX). sulfamethoxazole (S MZ), sulfamethoxydiazine (SMD) and sulfathiazole (STZ).The drugs were given by intravenous (iv.) of intraruminal route in dwarf goats. Heparin zed blood samples (2m1 each) were obtained from a indwelling jugular catheter, After centrifugation, samples were assayed using HPLC method, After iv. injection, the mean t -“b walues were for SMX, SMZ. SMD and STZ: 2. 35h. 1.04h. 3.36hand 0.80 h. respectively; mean Vd walues were: 0.23 1/kg, 0.221/kg 0.33 1/kg and 0.25 1/kg. Atrer oral administration, the mean BA values varied from 46.6% for SMX, 19.95% for SMZ, 86.0% for SMD and 52.6% for STZ. Eliminationhalf- life values were significantly prolonged, probably due to a slow rate of drug absorption.
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