Development and validation of a high-performance liquid chromatography-tandem mass spectrometry assay quantifying vemurafenib in human plasma.

Vemurafenib is an inhibitor of mutated serine/threonine-protein kinase B-Raf (BRAF) and is registered as Zelboraf((R)) for the treatment of adult patients with BRAF V600 mutation-positive unresectable or metastatic melanoma. To support Therapeutic Drug Monitoring (TDM) and clinical trials, we developed and validated a method for the quantification of vemurafenib in human plasma. Additionally two LC-MS systems with different detectors were tested: the TSQ Quantum Ultra and the API3000. Human plasma samples were collected in the clinic and stored at nominally -20 degrees C. Vemurafenib was isolated from plasma by liquid-liquid extraction, separated on a C18 column with gradient elution, and analysed with triple quadrupole mass spectrometry in positive-ion mode. A stable isotope was used as internal standard for the quantification. Ranging from 1 to 100mug/ml the assay was linear with correlation coefficients (r(2)) of 0.9985 or better. Inter-assay and intra-assay accuracies were within +/-7.6% of the nominal concentration; inter-assay and intra-assay precision were within