DETERMINATION OF MOXIDECTIN IN PLASMA BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH AUTOMATED SOLID-PHASE EXTRACTION AND FLUORESCENCE DETECTION

Moxidectin is a newly developed potent anthelmintic agent with a high potency although present at very low concentration in cattle plasma. A method is described for the determination of moxidectin in plasma usi ng high-performance liquid chromatography with fluorescence detection (excitation and emission wavelengths 383 and 447 nm, respectively). Th e fluorescent derivative was obtained by a dehydrative reaction with t rifluoroacetic anhydride and N-methylimidazole. The method employs 1-m l plasma samples and has linear calibration graphs (r = 0.997) over th e concentration range studied, i.e., 0.1-10 ng/ml. Solid-phase extract ion using the Benchmate procedure was used for sample preparation. Rec overies at low concentrations (0.1-10 ng/ml) were higher than 75%. The limit of quantification was 0.1 ng/ml (C.V. 6.95%). The method is sui table for the pharmacokinetic study of moxidectin after subcutaneous a dministration to cows.