Sirolimus (Rapamune®) - Effect of Different Assays on Therapeutic Drug Monitoring
January 13, 2010
Wyeth and FDA informed healthcare providers of changes to the prescribing information for sirolimus (Rapamune®) regarding different reference ranges for measuring blood concentrations. Sirolimus concentrations can be measured by chromatographic or immunoassay methods. The results from these assays are not interchangeable. In order to correctly adjust the dose, the prescriber must know which particular assay and laboratory were used for sirolimus therapeutic drug monitoring (TDM). Otherwise, incorrect dosing can result in drug concentrations outside the desired range, leading to either toxicity or allograft rejection. The sirolimus prescribing information was updated to reflect these inter-assay and inter-laboratory differences in sirolimus TDM.
Wyeth recommends all healthcare providers communicate closely with their laboratories. When monitoring patients on sirolimus, ask which assay is currently used at the local laboratory, in order to determine the correct therapeutic concentration. Encourage laboratories to communicate regularly with healthcare providers about any changes in assays or therapeutic range of sirolimus.
Additional information is available at the following links:
- MedWatch Alert:
- Dear Healthcare Professional Letter – Wyeth:
- Updated package insert:
January 13, 2010; University of Utah, Drug Information Service. Copyright 2010, Drug Information Service, University of Utah, Salt Lake City, UT.