A LC/MS/MS micro-method for human plasma quantification of vemurafenib. Application to treated melanoma patients

As previously shown for imatinib, therapeutic drug monitoring (TDM) of vemurafenib should be important to measure efficacy of the treatment in melanoma patient. A micro-method based on liquid chromatography coupled to triple quadrupole spectrometry detection using only 10μL of plasma was validated. A simple protein precipitation with water/acetonitrile was used after addition of vemurafenib-(13)C6 as internal standard. The ion transitions used to monitor analytes were m/z 490.2→m/z 255.2 and m/z 383.3 for vemurafenib and m/z 496.2→m/z 261.2 and m/z 389.3 for vemurafenib-(13)C6. Calibration curves were linear in the 0.1-100μg/mL range, the limits of detection and quantification being 0.01μg/mL and 0.1μg/mL, respectively. The intra- and inter-assay precisions evaluated at 0.1, 0.3, 15, 45 and 80μg/mL were lower than 13.3% and the accuracies were in the 93.7-105.8 range. No matrix effect was observed. At steady state, the results of TDM of vemurafenib in 26 patients treated by 960mg twice daily (n=60 samples), 13 patients with 740mg twice daily (n=13) and one with 1200mg twice daily (n=3) showed a great variability of the pharmacokinetics of this compound.