Comparative measurement of abamectin, ivermectin and moxidectin concentrations in resistant Haemonchus contortus.

LIFSCHITZ, A.; LLOBERAS, M.; ALVAREZ, L.; ENTROCASSO, C.; BALLENT, M.; VIRKEL, G.; MATÉ, L.; LANUSSE, C.

Congreso; 23 International Conference of the World Association for the Advancement of Veterinary Parasitology; 2011

AAVP

Abamectin (ABM), ivermectin (IVM) (avermectins) and moxidectin (MXD) (milbemycin) are close related broad-spectrum endectocide compounds. However, differential efficacy patterns against resistant nematodes have been reported, which may be based on specific pharmacokinetic/pharmacodynamic features of each molecule. This work aimed to measure the comparative concentration profiles of ABM, IVM and MXD achieved in the bloodstream, the gastrointestinal contents/tissues and within a target abomasal parasite (H. contortus) in lambs naturally infected with resistant nematodes. Additionally, the pattern of the drug-transporter P-glycoprotein (P-gp) mRNA expression in H. contortus exposed to the three compounds was established. Thirty (30) naturally parasitized lambs were assigned into three experimental groups intraruminally treated with either ABM, IVM or MXD at 0.2 mg/kg. Blood samples were collected from six animals in each treated group over 14 days post-treatment. Four animals from each group were sacrificed at day 2 post-treatment. Mucosal and fluid content samples from the abomasum and small intestine were collected. Adult specimens of H. contortus were recovered from the abomasum. Drug concentrations were measured by HPLC. Specific P-gp mRNA levels in H contortus were quantified by PCR. A similar plasma systemic exposure (expressed as AUC values) was obtained for the endectocide molecules. However, MXD persistence in the bloodstream was longer (P