Background: Regorafenib is a multikinase inhibitor, indicated for the treatment of metastatic
colorectal cancer and locally advanced, unresectable or metastatic gastrointestinal stromal tumor.
Objective: A simple and fast, validated bioanalytical method is required for pre-clinical or clinical
safety and efficacy investigations and possible pharmacokinetic interaction of regorafenib.
Method: Regorafenib and sorafenib were eluted on Acquity UPLC®BEH C18 column. Elution was
carried out by pumping mobile phase [methanol (0.1% formic acid): water (85:15%)] at 200µl/min flow
rate. Mass detector was operated in multiple-reaction monitoring mode. Deprotonated ions [M-H]- of
regorafenib and sorafenib were fragmented and monitored.
Results: Daughter fragments of regorafenib (m/z 481.1 > 194, m/z 481.1 > 260) and sorafenib (m/z 463
> 193.99, m/z 463 > 268.1) were determined in negative electrospray ionization mode. Linear calibration
curve of range 50-2500 ng/ml was prepared in plasma. Method was selective, since there was no
interfering peak at regorafenib retention time. Coefficients of variation for inter-day precision at three
quality control concentrations were 17.6% at lower limit of quantitation, 6.3% at middle limit, and 2.9%
at the highest limit of quantitation. Accuracy of the method ranged between 96% to 105.3%. Recovery
of drug from blank plasma at quality control concentrations varied between 82.53 to 105.66%.
Conclusion: The developed method was successfully validated by adopting US FDA guidance for
bioanalytical methods. The method is simple, quick and can be adopted for regorafenib estimation in
other biological fluids with necessary modifications.