Failure of systematic error detection with internal quality control program.

Everolimus (Certican,® Novartis Pharma AG, Basel, Switzerland), a macrolide antibiotic derived by chemical modification of a natural product, sirolimus (Rapamune,® Wyeth-Ayerst, Princeton, NY, USA), is a potent immunosuppressive agent that prevents the rejection of solid organ grafts [1, 2]. Therapeutic drug monitoring (TDM) plays a key role in maintaining blood everolimus concentrations within the narrow therapeutic range and helps to optimize the dosage regimen, maintain immunosuppressive efficacy, and minimize toxicity [3]. For the detection of analytical errors in TDM, quantification of control materials is generally effective, as routinely done in clinical chemistry laboratories. However, we recently experienced an episode in which the internal quality control procedure for everolimus, which uses control materials provided by the same manufacturer as the reagent, failed to detect a systematic error in the analysis of patient samples.