FDA Video: Measuring Rapamune Blood Concentrations

Wyeth is cautioning healthcare professionals about therapeutic drug monitoring for Rapamune (sirolimus). Rapamune is used to prevent organ rejection in certain renal transplant patients.

The company points out that Rapamune blood concentrations can be assayed using either chromatographic or immunoassay tests, and that the results of these two methodologies are not interchangeable. If the assay method were switched during a patient's treatment with Rapamune, the dose of the drug might be adjusted improperly - too low a dose could lead to allograft rejection, and too high a dose could expose the patient to toxic side effects.

Wyeth is advising clinicians who manage patients on Rapamune to determine which assay is used in their laboratory, if there has been any change in the assay or in the laboratory's reference range, and if the institution or referring center has changed its recommended range. The bottom line is that it is critical for clinicians to communicate with their laboratories about any changes in the assays used to measure blood concentrations in Rapamune patients.