Bioavailability of levamisole after intramuscular and oral administration in sheep

To determine the bioavailability of levamisole in sheep.

Levamisole was administered to three groups of six Merino sheep orally and intramuscularly at three dose levels of 5, 7.5 and 10 mg/kg. There was a washout period of 1 week between treatments. Blood samples were collected by jugular venepuncture and plasma was separated immediately by centrifugation and stored at 20 degrees C until analysed. The levamisole concentration in plasma was determined by high performance liquid chromatography with a U.V. detection method. Individual plasma levamisole concentration-time data were analysed using the compartmental method.

The values obtained for k(a), C(max), t(max) and F show a moderate rate and extent of absorption after oral administration of levamisole while, after intramuscular administration, these values demonstrate a high rate and extent of absorption of levamisole. The intramuscular bioavailability was higher than the oral bioavailability (rate of absorption three-fold faster, extent of absorption 25-33% higher and C(max) two-fold higher). The Friedman test involving dose and route of administration showed that the route of administration affects k(a), C(max), t(max) and F; significant differences were found in these parameters.

On the basis of these data, the recommended routes for the administration of levamisole in sheep are oral for gastro-intestinal nematodiasis and intramuscular for extragastric nematodiasis.