Tandem mass spectrometry Reactive metabolites

Yan, Z. et al. 2005. Rapid detection and characterization of minor reactive metabolites using stable-isotope trapping in combination with tandem mass spectrometry. Rapid Commun. Mass Spectrom. 19 3322. 

Ma, S., and Subramanian, R. (2006). Detecting and characterizing reactive metabolites by liquid chromatography/tandem mass spectrometry. J. Mass Spectrom. 41 1121-1139. 

Soglia, J. R., Contillo, L. G., Kalgutkar, A. S., Zhao, S., Hop, C. E. C. A., Boyd, J. G., and Cole, M. J. (2006). A semiquantitative method for the determination of reactive metabolite conjugate levels in vitro utilizing liquid chromatography-tandem mass spectrometry and novel quaternary ammonium glutathione analogs. Chem. Res. Toxicol. 19 480-490. 

The first procedure available for analysis of cyclosporine was an RIA developed by Sandoz Pharmaceuticals, the producer of cyclosporine. This immunoassay exhibits approximately 30% cross-reactivity with inactive metabolites, and the test is now considered obsolete. Nonisotopic immunoassays have been developed for whole-blood analysis. HPLC methods have been developed and are used now by many laboratories. A practical HPLC tandem mass spectrometry method is included on this book s accompanying Evolve site, found at http //evolve.elsevier.com/Tietz/ textbook/. 

Ma, S. and Zhu, M., Recent advances in applications of liquid chromatography-tandem mass spectrometry to the analysis of reactive drug metabolites, Chem. Biol. Interact., 179(1), 25, 2009. 

The commonly used methods for the determination of these drugs are immunoassays and chromatography. Most immunoassays for immunosuppressants are semiautomated since extraction of drugs from the whole blood is needed before analysis. Immunoassays are convenient due to automation, but have problems with cross-reactivity with drug metabolites (3, 6). Both polyclonal and monoclonal antibody-based assays are available. Monoclonal antibody-based immunoassays are more specific. HPLC with ultraviolet detection and tandem mass spectrometry are commonly used chromatographic methods for the assay of immunosuppressants. Due to their specificity and sensitivity, tandem mass spectrometry assays are preferred and are now in wide use (7, 8). The other major advantage of tandem mass spectrometry assays is their ability to simultaneously measure several immunosuppressants (7-10). Pharmacokinetic properties of CSA, sirolimus, and tacrolimus are shown in Table 1 (3, 6, 11). 

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