Bioavailability study of phenylbutazone in cattle
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The bioavailability of phenylbutazone was investigated in six adult cattle in a crossover study after intravenous and oral administration of the drug at a dose rate of 4.4 mg/kg. The drug concentration in plasma was determined in each administration route. The mean bioavalilability for the granular formulation was 56.9 and a considerable variation between animals occurred. The mean maximum plasma concentration (Cmax) and time of maximum concentration (Tmax) values were 23.9 no. 2ug/ml and 10.5 no. 1.9h respectively. The area under the curve (Auc) for the drug was 1 629 no. 221 ug/ml.h and double peaks were found in the plasma concentration time curves in some animals after oral administration. The biphasic curves were attributed to direct absorption of the drug into plasma and adsorption of the drug on to hay.