Pharmacokinetics of ivermectin in the camel (Camelus dromedarius)

and sheep (238 ng/day/ml) (Marriner and others 1987), but similar to the value calculated for goats (60.77 ng/day/ml) (Alvinerie and others 1993). The MRT was about three times more in camels (21.50 days) than that reported in cows (6.54 days) (Toutain and others 1988) and goats (7.06 days) (Alvinerie and others 1993), suggesting a slower transit of ivermectin through the camel's body. From the efficacy point of view, the low ivermectin plasma concentrations in camels tend to suggest that a subcutaneous dose of 0.2 mg/kg, would be less effective in this species than in other ruminant species, especially cattle and sheep. However, according to field results, ivermectin at such a dose rate, has an excellent efficacy against the majority of the camel's endoand ectoparasites (Ibrahim and others 1981, Boyce and others 1984). This paradox could be explained by the longer duration of exposure of parasites to lower concentrations of ivermectin, since it has been shown that anthelmintics' efficacies increase when they are delivered as divided doses (Prichard and others 1978). Finally, the results obtained in the present investigation may have interesting public health implications, because of major differences observed in ivermectin pharmacokinetic behaviour between camels and other ruminant species. So, it is reasonable to conclude that ivermectin concentrations of residues in edible tissues and milk, and consequently withdrawal times in the camel would also be different from those reported in other ruminant species. However, these results should be confirmed in a larger group of camels. Acknowledgements. The authors thank Dr D. W. Johnson and Dr P. L. Toutain for correcting this manuscript, and Mr S. Suilahi, Mr M. Ablouh and Mrs J. Assal for technical assistance.