title: Comparative plasma disposition, bioavailability and efficacy of ivermectin following oral and pour-on administrations in horses.
abstract: Pour-on formulations of endectocides decrease the risk of injury for both user and animal, and are particularly convenient for animal owners who can apply the product. This study was designed to investigate the plasma disposition and efficacy of ivermectin (IVM) following pour-on, per os and intravenous administrations. Eighteen female horses weighing 510-610 kg were used in this study. The animals were allocated into three groups (per os, pour-on and intravenous groups). The equine paste, bovine pour-on and bovine injectable formulations of IVM were administered orally, topically and intravenously at the dose rates of 0.2, 0.5 and 0.2mg/kg bodyweight, respectively. Heparinized blood samples and hair samples were collected at various times between 1h and 40 days. The samples were analysed by high performance liquid chromatography with fluorescence detector. Faecal strongyle egg counts (EPG) were performed by a modified McMaster's technique before and at weekly intervals during 10 weeks after treatment. The results indicated that the plasma concentration and systemic availability of IVM was lower but the plasma persistence was prolonged after pour-on administration compared with per os route. IVM (paste) reduced the EPG by >95% for 10 weeks, whereas the reduction in pour-on group varied from 82 to 97%. EPG reduction in pour-on group was lower than that of per os group. Degradation on the application site, cutaneous biotransformation, binding of IVM to the haircoat and/or sebum are probably responsible for the relatively lower bioavailability of IVM in horses after pour-on administration. In conclusion, the poor plasma availability observed after pour-on administration could result in subtherapeutic plasma concentrations, which may promote the development of drug resistance in parasites.
authors.affiliation: Department of Pharmacology and Toxicology, Faculty of Veterinary Medicine, Adnan Menderes University, Isikli Koyu, 09100 Aydin, Turkey. cengizgokbulut@yahoo.com
authors.forename: Cengiz
authors.initials: C
authors.lastname: Gokbulut
authors.forename: Veli Y
authors.initials: VY
authors.lastname: Cirak
authors.forename: Bayram
authors.initials: B
authors.lastname: Senlik
authors.forename: Dilek
authors.initials: D
authors.lastname: Aksit
authors.forename: Murat
authors.initials: M
authors.lastname: Durmaz
authors.forename: Quintin A
authors.initials: QA
authors.lastname: McKellar
mesh_terms: D000284:Administration, Oral; D000287:Administration, Topical; D000818:Animals; D000977:Antiparasitic Agents / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D019540:Area Under Curve; D005243:Feces / Q000469:parasitology; D005260:Female; D006207:Half-Life; D006734:Horse Diseases / Q000188:drug therapy / Q000469:parasitology*; D006736:Horses; D007273:Injections, Intramuscular / Q000662:veterinary; D007559:Ivermectin / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D010270:Parasite Egg Count / Q000662:veterinary; D017206:Strongylida Infections / Q000188:drug therapy / Q000469:parasitology / Q000662:veterinary*; D013323:Strongylus / Q000254:growth & development*
chemical_list: D000977:Antiparasitic Agents; D007559:Ivermectin