Successive treatments with ivermectin (3.15%) to control the tick Rhipicephalus (Boophilus) microplus in cattle: Pharmacokinetic and efficacy assessment

SARLI, MACARENA; MIRÓ, MARÍA VICTORIA; ROSSNER, MARÍA VICTORIA; NAVA, SANTIAGO; LIFSCHITZ, ADRIÁN

Ticks and Tick-borne Diseases

Elsevier

Año: 2022 vol. 13

1877-959X

This study aimed to evaluate the pharmacokinetics, the potential accumulation in the body of treated animalsand the efficacy of ivermectin long-acting formulation (3.15%) against the cattle tick Rhipicephalus (Boophilus)microplus in a scheme of three successive treatments. Fifteen 12-month-old heifers, naturally infested withR. microplus, were divided into two groups (G). Cattle from GI (n = 10) were subjected to three treatments withivermectin 3.15% (IVOMEC GOLD®, Merial Argentina S.A.) at a rate of 1 mL/50 kg on days 0, 35, and 70. Cattlefrom GII (n = 5) were not treated. From day 1 to 202 post-treatment blood samples were taken to measureivermectin concentrations by HPLC and female ticks (4.5?8 mm) were counted to evaluate the efficacy of thetreatment. The level of tick resistance to ivermectin was evaluated before and after finishing the scheme ofsuccessive treatments by larval immersion test (LIT) bioassay from engorged females collected from GI. The areaunder the concentration vs. time curves (AUC0?35d) obtained post-second treatment was 1.51 ± 0.39-fold higherthan those observed post-first treatment (P<0.05). The mean plasma concentrations of ivermectin 3.15% at 20days after the first, second and third treatment were 17.0, 27.5 and 37.8 ng/mL, respectively (P<0.01). Theelimination half-life of ivermectin post-third treatment was significantly longer than that was previously reportedafter a single dose (P<0.01). Values of therapeutic efficacy percentage reached 75.6% post-first treatment andbetween 95.9 and 100% after the second treatment. Ticks evaluated by LIT showed a significant increase in lethalconcentrations after treatments. Although the efficacy level was high, the successive treatments with long-actingivermectin formulation generate a significant accumulation of drug in plasma and could increase the levels ofresistance to this drug in the tick population.