Determination of the muscarinic agent [(3-(3-1-butylthio)-1,2,5-thiadiazol-4-yl)-1-azabicyclo-2.2.2-oct ane], in rat, rabbit, and monkey plasma, using high-performance liquid chromatography in conjunction with tandem mass spectrometry.

A method for determining a selective muscarinic agent, LY297802 (compound I), [(3-(3-1-butylthio)-1,2,5-thiadiazol-4-yl)-1-azabicyclo-2.2.2-octa ne], indicated in the treatment of pain, in rat, rabbit, and monkey plasma is described. The analytes, including an internal standard, were extracted from plasma at basic pH with hexane. The organic fraction was evaporated to dryness and the residue reconstituted with mobile phase. The analytes were detected utilizing HPLC in conjunction with electrospray (ES) tandem mass spectrometry (MS-MS). The limit of quantitation was 0.25 ng/ml, and the response was linear to at least 100 ng/ml.

Determination of dapoxetine, an investigational agent with the potential for treating depression, and its mono- and di-desmethyl metabolites in human plasma using column-switching high-performance liquid chromatography.

A column-switching high-performance liquid chromatographic (HPLC) method is described for the determination of dapoxetine and its mono- and di-desmethyl metabolites in human plasma. The analytes, including an internal standard, were extracted from plasma at basic pH with hexane-ethyl acetate. The organic extract was evaporated to dryness and the residue reconstituted with acetonitrile. The analytes were separated from late-eluting endogenous substances on a Zorbax RX-C8 pre-column. The front-cut fraction containing the analytes was further separated on a second RX-C8 column. The analytes were detected by their native fluorescence, using excitation and emission wavelengths of 230 and 330 nm, respectively. The limit of quantitation was determined to be 20 ng/ml, and the response was linear from 20 to 200 ng/ml. The method has been successfully applied to human plasma samples in a Phase I study.

Metabolism and disposition of gemcitabine, and oncolytic deoxycytidine analog, in mice, rats, and dogs.

Gemcitabine, 2'-deoxy-2',2'-difluorocytidine, is a broad spectrum oncolytic compound with antitumor activity in solid tumor models. The pharmacokinetics, metabolism, and disposition of gemcitabine was examined in mice, rats, and dogs. All three species metabolize gemcitabine by deamination to the uracil metabolite. However, deamination in the mouse and dog was more extensive than in the rat. The mouse deaminated gemcitabine rapidly with the plasma concentration maximum of the uracil metabolite of gemcitabine being attained at 15 min postdosing compared with approximately 3 and 6 hr in the dog and rat, respectively. The rapid deamination in the mouse was also reflected in the plasma half-life of the parent compound. The mouse exhibited the shortest plasma half-life, approximately 0.28 hr, contrasted with 2.14 and 1.38 hr half-lives in rat and dog, respectively. Plasma AUC for the uracil metabolite of gemcitabine was 73%, 10.5%, and 315% of that for gemcitabine in the mouse, rat, and dog, respectively. Tissue concentrations of gemcitabine-derived radioactivity in the rat and mouse indicated that gemcitabine was rapidly distributed throughout the body. Half-lives of radioactivity in tissues of both the rat and mouse were relatively short, with the longest tissue half-lives of 5.7 and 3.0 hr, respectively. Plasma protein binding is negligible in all three species. The major route of elimination is via the urine in all three species with 76-86% of the dose excreted in the first 24 hr. The predominant radiolabeled component isolated from urine was gemcitabine in the rat and its uracil metabolite in the mouse and dog.