An Enhanced Avermectin Extraction Method for Characterization of Bovine Pharmacokinetics Utilizing Tandem Mass Spectrometry

Babesia bigemina and B. bovis are protozoans spread amongst livestock by certain species of ticks, known collectively as cattle fever ticks (CFTs), and cause the chronic disease bovine babesiosis. Although eradicated from the US in 1940s, CFT and Babesia are endemic to Mexico, Central and South America. CFT continue to infiltrate the US by crossing the border on wildlife or stray livestock and infest cattle herds. Avermectins are a class of anti-tick drugs administered to cattle to prevent and control tick infestation. Texas A&M University in collaboration with the US Department of Agriculture (USDA) conducted a doramectin (DOR) dosing study to evaluate how a double dose of DOR might extend the window of protection versus a single dose. We developed and validated a sensitive liquid chromatography/ tandem mass spectrometry (LC-MS/MS) method for analysis of the study’s samples. Presented here are an enhanced analytical method for this lipophilic class of drugs, the DOR plasma concentrations from the study, and the relevant pharmacokinetic parameters.