Failure of ivermectin and eprinomectin to control Amblyomma parvum in goats: Characterization of acaricidal activity and drug pharmacokinetic disposition

ADRIAN LIFSCHITZ, SANTIAGO NAVA, ALBERTO A GUGLIELMONE, FERNANDA IMPERIALE, CRISTINA FARIAS, ATILIO J MANGOLD, CARLOS LANUSSE.

VETERINARY PARASITOLOGY

Año: 2008 vol. 156 p. 284 - 292

0304-4017

The therapeutic efficacies of ivermectin (subcutaneous injection) and eprinomectin (topical treatment) given at two differentdosage levels to goats naturally infested with Amblyomma parvum were assessed. Treatments included subcutaneous injection ofivermectin at 0.2 and 0.4 mg/kg and extra-label pour-on administration of eprinomectin at 0.5 and 1 mg/kg b.w. Ivermectin andeprinomectin failed to control Amblyomma parvum on goats. Treatment with ivermectin resulted in a low number of engorgedfemale ticks in relation to untreated control goats and, at the highest dose rate (0.4 mg/kg), the female engorgement weights weresignificantly lower and the pre-oviposition period significantly longer than those observed in ticks recovered from untreated controlgoats. The tick efficacy assessment was complemented in a separate group of tick-free goats with a pharmacokinetic characterizationof eprinomectin (topically administered at 0.5, 1.0 and 1.5 mg/kg) and ivermectin (subcutaneous treatment given at (0.2 and0.4 mg/kg) in goats. Heparinized blood samples were taken between 0 and 21 days post-treatment. Higher and more persistent drugplasma concentrations were recovered after the subcutaneous treatment with ivermectin compared to those obtained foreprinomectin topically administered. The understanding of the relationship among the pattern of drug absorption, the kineticdisposition and the resultant clinical efficacy is relevant to improve the poor performance observed for ivermectin and eprinomectinagainst A. parvum on goats.