Moxidectin Intoxication to be Studied at the University of Kentucky

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Researchers at the University of Kentucky (UK) Department of Veterinary Science received a $19,285 Koller Fund grant to study the pharmacokinetics of moxidectin, a type of avermectin dewormer. Moxidectin is used to treat and prevent external and internal parasites in horses and other species.

Cindy Gaskill, DVM, PhD, a clinical veterinary toxicologist at the UK Veterinary Diagnostic Laboratory (UKVDL); Martin Nielsen, DVM, PhD, EVPC, an assistant professor at the UK Gluck Equine Research Center; and Lori Smith, PhD, a senior chemist of toxicology at the UKVDL, are the primary investigators named in the grant.

Macrocyclic lactone (ML) anthelmintic intoxication can occur in horses from overdoses, from interactions with other drugs or plant compounds or from inappropriate dosing of very young or old animals. Signs of ML intoxication occur due to excessive accumulation of the drugs in the brain. Confirming ML poisoning as a cause of death can be difficult, especially if the owner provides no history of known exposure. The best post-mortem confirmatory test is by measuring drug concentrations in the brain tissue.

The UKVDL has recently received a number of horses for post-mortem evaluation with histories of neurologic abnormalities and suspected exposure to the ML anthelmintic moxidectin at unknown doses. Several of the horses came from Central Kentucky farms.

As stated in the grant proposal, “Results of this study will help confirm or reject a diagnosis of moxidectin intoxication in these horses.”

The grant will also help researchers determine the levels of post-therapeutic dosing brain concentrations of moxidectin in horses and develop a quantitative HPLC (high performance liquid chromatography) method for macrocyclic lactone anthelmintic (i.e., moxidectin and ivermectin) analyses in equine brain tissue.