Sirolimus: different immunoassays for therapeutic drug monitoring—risk of incorrect dose adjustment

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Article date: March 2010

Sirolimus (Rapamune▼) is indicated for the prophylaxis of organ rejection in adult patients at low to moderate immunological risk receiving a renal transplant.

Optimal therapy requires therapeutic drug concentration monitoring in all patients. Adjustments to the targeted therapeutic dose range of sirolimus must only be made with a detailed knowledge of the specific assay used to measure the drug concentration in the patient.

Currently, sirolimus whole-blood concentrations are measured using either the reference assay high performance liquid chromatography (HPLC), or an immunoassay. Switching between different immunoassays, or between an immunoassay and HPLC, in a single patient can lead to clinically significant differences in results, and therefore, incorrect dose adjustments. This, in turn, may have potential adverse consequences, such as allograft rejection if drug exposure is too low or toxic side effects if exposure is too high.

A letter has been sent to healthcare professionals in February 2010 to encourage prescribers to regularly contact their laboratory and ascertain whether the assay used recently has been changed and whether there have been any changes to the laboratory’s reference range.

 

Article citation: Drug Safety Update March 2010, vol 3 issue 8: 5a.

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