Eprinomectin accumulation in Rhipicephalus (Boophilus) microplus: Pharmacokinetic and efficacy assessment

LIFSCHITZ, A.; NAVA, S.; MANGOLD, A. J.; IMPERIALE, F.; BALLENT, M.; CANEVARI, J.; LANUSSE, C.

VETERINARY PARASITOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2016 p. 11 - 16

0304-4017

Eprinomectin (EPM) is a macrocyclic lactoneused against endo-ectoparasites without withdrawal time in milk and meat afterits pour-on administration at 0.5 mg/kg. Previous experiments evaluated theefficacy of EPM against Rhipicephalus (Boophilus) microplus in cattle. Thisstudy assessed EPM efficacy against R. (B.) microplus after topicaladministration at two dose rates and investigated the relationship between EPMsystemic exposure in the host and drug concentrations accumulated in ticksrecovered from treated animals. A standardized pharmaco-parasitological studywas performed in two phases. In phase 1 eighteen Braford cattle naturallyinfected with R. (B.) microplus were divided into three experimental groupswith a similar level of infestation (Kruskal?Wallis test, P > 0.05): controlgroup and treated groups with EPM pour-on (1 and 1.5 mg/kg). Samples ofheparinized blood and ticks at different life stages were taken between 0 and21 days (d) post-administration to measure EPM concentrations by HPLC. Theefficacy trial (phase 2) included eighteen Braford calves naturally infectedwith R. (B.) microplus divided into control group and 1 mg/kg and 1.5 mg/kg EPMtreated groups. Female ticks (4.5?8 mm) on cattle were counted between 1 and 23days post-treatment to evaluate the efficacy of EPM. The reproductiveefficiency index (REI) and the fertility efficiency index (FEI) were evaluated.Plasma concentrations of EPM showed a linear relationship with the level ofdose rate administered. Peak plasma concentrations were within a range between13.8 and 90 ng/ml, which guarantee milk drug concentrations below the maximumresidues level. High EPM concentrations were detected in ticks. EPMconcentrations in R. (B.) microplus were correlated to plasma concentrationsbetween 1.25 days and 21 days post-administration (r 0.84; P < 0.05). EPMefficacy calculated using the Henderson?Tilton formula was 98.9% and 99.1% (7days post-administration) and 100% (23 days post-administration) after EPMtreatment at 1 and 1.5 mg/kg, respectively. EPM administered at 1.5 mg/kg alsoshowed a significantly higher deleterious effect on tick fertility as measuredby FEI (P < 0.01). Therefore, treatment with EPM may be useful forcontrolling ticks in cattle, particularly in dairy production systems.