The route of administration drastically affect ivermectin efficacy against small strongyles (Cyathastominae) in horses

SAUMELL CARLOS A.; LIFSCHITZ ADRIÁN L.; BARONI RENATO ; FUSE LUIS.; BISTOLETTI M.; SAGÜÉS MARÍA F.; SANTIAGO BRUNO; LANUSSE C.; ALVAREZ L.

VETERINARY PARASITOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2017 vol. 236 p. 62 - 67

0304-4017

The goal of the current work was to evaluate the efficacy of ivermectin (IVM) against small strongyles (cyathostomins) in naturally parasitized horses, after its administration by the oral or the intramuscular (IM) route. Additionally, the plasma disposition kinetics of IVM was assessed. The current trial include two different experiments, Experiment I and Experiment II. In Experiment I, forty horses naturally infected with small strongyles were randomly allocated into four experimental groups (n= 10), and treated with IVM (0.2 mg/kg) as follow: Eqvalan, animals were treated with Eqvalan® (IVM 1.87% paste) by the oral route; Remonta (oral), animals were treated with Remonta® (IVM 2% solution) by the oral route; Remonta (intramuscular), animals were treated with Remonta® by the intramuscular (IM) route; and Control, animals were kept without treatment as controls. In Experiment II, 24 horses naturally parasitized with small strongyles were randomly allocated into the same four experimental groups (n= 6) described for Experiment I. Faecal individual samples were collected directly from the rectum pre-treatment (day -1) and at 7 and 15 (Experiment I) or 7, 15 and 21 (Experiment II) days post-treatment, to assess the eggs per gram (epg) counts and estimate the efficacy of the treatments. Additionally, the comparative plasma disposition kinetics of IVM in treated animals was assessed in Experiment II. In both experiments, an excellent (100%) IVM efficacy was observed after its oral administration (Eqvalan or Remonta formulations). However, the IM administration of IVM, results in a low efficacy (36-64%). Similar IVM plasma exposure was observed after its oral administration as a paste (Eqvalan) or a solution (Remonta). The higher IVM plasma profiles observed after its IM administration, accounted for an enhanced systemic availability. The improved IVM efficacy against adult cyathostomins obtained after the oral administration can be explained by an enhanced drug exposure of the worms located at the lumen of the large intestine. Such a finding may have direct impact on the practical use of the macrocyclic lactones in horses.