Semi-automated quantification of ivermectin in rat and human plasma using protein precipitation and filtration with liquid chromatography/tandem mass spectrometry.

Ivermectin is a parasiticide commonly used in humans and livestock. It is currently under development for the treatment of pediculosis of humans (head lice) that does not respond to established treatments. A liquid chromatography/turbo ion spray tandem mass spectrometry (LC/TIS-MS/MS) method for the determination of ivermectin in rat and human plasma has been developed that uses emamectin [4"-epi-(methylamino)-4"-deoxyavermectin] as the internal standard. Sample preparation involved protein precipitation and filtration of fortified plasma in the 96-well format. Chromatographic separation was accomplished using fast gradient conditions on a C8 stationary phase. The analytes were detected with the mass spectrometer operated in the positive ion, multiple reaction monitoring mode. The method exhibited good intra- and interday accuracy and precision, and was linear over a dynamic range of 1-2000 ng/mL. In rat plasma, intraday accuracy ranged between 84-93% for the low quality control (QC) sample (1.5 ng/mL), and between 91-109% for the remaining QCs. Intraday precision ranged between 4.9-15% for the low QC, and 0.8-6.3% for the remaining QCs. Interday accuracy ranged between 88-107%, and precision between 4.1-11%. Similar data was obtained using human plasma. An investigation of matrix effects indicated that the ionization efficiency of ivermectin was favored by the presence of an ammonium ion in an aqueous environment. The implications of this observation toward assay sensitivity are discussed.