A sensitive method for the measurement of the novel pet endectocide, selamectin (UK-124,114), in dog and cat plasma by chemical derivatisation and high-performance liquid chromatography with fluorescence detection

An analytical method has been developed for the novel pet endectocide, sela mectin (USAN, UK-124, 114), in dog and cat plasma to facilitate pharmacokin etic profiling for this compound. The method involves solid phase extractio n of the compound and internal standard from plasma followed by chemical de rivatisation using triethylamine and trifluoroacetic anhydride. This reacti on yields a highly fluorescent product and thus provides a sensitive assay. Using a sample Volume of 1.0 mi for dog plasma the assay has been validate d over a concentration range of 0.2-40 ng/ml. Due to smaller plasma volumes for cat plasma samples. the assay was validated over a concentration range of 1.0-200 ng/ml using a sample volume of 0.2 mi. The analyte has been sho wn to be stable for 48 h at room temperature and through three freeze-thaw cycles in dog plasma. The analytical method is highly specific and proved s uitable for the analysis of selamectin in dog and cat plasma samples follow ing doses of compound by parenteral and non-parenteral routes. (C) 2000 Els evier Science B.V. All rights reserved.