Everolimus is an immunosuppressant primarily used to prevent organ rejection in transplant patients. The drug is marketed under the tradenames Zortress® and Certican® for use in organ transplantation and Afinitor® for treatment of kidney and pancreatic cancers. Immunosuppressive drugs require clinical monitoring since they act within a narrow therapeutic range of concentrations and show large differences among individual patients in drug handling and efficacy. Regular clinical monitoring is necessary to avoid acute renal or gastrointestinal toxicity or an increase in risk of infection during the treatment regimen. 

Clinical laboratories quantitate everolimus levels in patient whole blood samples using LC-MS/MS. The presence of an internal standard in the sample is important to minimize sample-dependent changes in extraction or different ionization characteristics. Effectiveness of the internal standard is dependent on the extent of its structural difference from everolimus. While many everolimus LC-MS/MS methods use 32-desmethoxyrapamycin or ascomycin as an internal standard, higher levels of variability / lower levels of reproducibility may occur in the analysis along with the potential for interferences. Use of a stable-labeled analog of everolimus is the best choice to minimize variability or mitigate any potential interference in LC-MS/MS analysis.

Everolimus-d4 was synthesized and certified for use as an internal standard in LCMS applications.  It was certified for use as a reference material by testing for chromatographic purity, isotopic purity and residual impurities.  Use of the standard in LCMS applications was demonstrated by quantitation of an everolimus control sample against a calibration curve.  The product is suitable for use as internal standard for analysis of everolimus and other immunosuppressants by mass spectrometry.