Pharmacokinetics of eprinomectin in lactating ewes following administration of a subcutaneous formulation of eprinomectin

Eprecis® 2% (Ceva Santé Animale) is a subcutaneous formulation of eprinomectin that has been recently registered in cattle at a dose rate of 0.2 mg/kg without milk withdrawal period. In order to precise the optimal dose rate of this new formulation in sheep, we performed a pharmacokinetic study in lactating ewes at 0.2 and 0.4 mg/kg. Additionally, we determined the milk residue profile associated with the optimal dose rate.

Eprinomectin plasmatic concentrations following subcutaneous administration of Eprecis ® 2% at either 0.2 mg/kg or 0.4 mg/kg were above the efficacy threshold (>2 µg/L) at all time during the study (figure 1). Consequently, it can be anticipated that the optimal dose rate for Eprecis® 2% in sheep is 0.2 mg/kg. At this dose rate, 96% of the milk samples did not have detectable eprinomectin residues and the 4% of eprinomectin positive samples (5 samples out of 128) presented concentrations widely below the published maximum residue level (MRL) (Figure 2).

Finally, in comparison with the topical formulation dosed at 1.0 mg/kg (Eprinex® Pour-on, Merial), subcutaneous formulation dosed at 0.2 mg/kg showed a higher AUClast (73.3 vs 48.8 day*ng/mL) and Cmax (19.5 vs 6.2 ng/mL), demonstrating a greater bioavailability with 5 times less active ingredient.