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(®) 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°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 100μg/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 ≤9.3% of the nominal concentration. In addition all results were within the acceptance criteria of the US FDA and the latest EMA guidelines for method validation for both MS detectors. In conclusion, the presented analytical method for vemurafenib in human plasma was successfully validated and the performance of the two LC-MS systems for this assay was comparable. In addition the method was successfully applied to evaluate the pharmacokinetic quantification of vemurafenib in cancer patients treated with vemurafenib.