STABILITY OF PENICILLIN-G, AMPICILLIN, AMIKACIN AND OXYTETRACYCLINE AND THEIR INTERACTIONS WITH FOOD IN IN-VITRO SIMULATED EQUINE GASTROINTESTINAL CONTENTS

Penicillin G was extensively (84.7 per cent) and amikacin moderately ( 14.4 per cent) degraded when incubated for one hour in a chloride buff er at pH 1.9 designed to mimic the equine gastric pH. Ampicillin and o xytetracycline were stable at pH 1.9. Penicillin and ampicillin were m oderately stable (more than 90 per cent) when incubated in equine caec al liquor for three hours but were degraded by about 65 per cent after 24 hours. More than 80 per cent of the initial concentrations of amik acin and oxytetracycline were recovered after 24 hours' incubation in equine caecal liquor. The concentrations of short chain fatty acids in equine caecal liquor were not affected by incubation with penicillin G, ampicillin, amikacin or oxytetracycline. More than 84 per cent of p enicillin G and amikacin became bound to hay in buffers at pH 1.9 and pH 7.0. Ampicillin did not become bound to hay at pH 1.9, but more tha n 60 per cent became bound at pH 7.0.