[Effects of Seven Tyrosine Kinase Inhibitors on the Anticoagulation Activity of Warfarin].

Several studies have reported increased anticoagulation effect of warfarin(WF)when combined with tyrosine kinase inhibitors(TKIs), such as gefitinib and erlotinib. However, effects of TKIs other than gefitinib and erlotinib on the anticoagulation effect of WF have not been clarified. To assess the degree and onset of prothrombin time-international normalized ratio (PT-INR)elevation and changes in WF daily doses in patients additionally receiving TKIs, this retrospective, single-center observational study compared PT-INR values and WF daily doses during WF treatment in the absence and presence of TKIs. Seven different TKIs(afatinib, alectinib, axitinib, crizotinib, pazopanib, regorafenib, and vandetanib)were prescribed during treatment with WF of venous thromboembolism in 10 cancer patients. Compared to baseline PT-INR, significant PT-INR elevations were observed in all patients during the combination therapy. The median PT-INR increased 1.6-fold from the baseline in the presence of TKIs(p<0.01), and the onset of PT-INR elevation was observed at a median of 18 days. As all patients receiving WF with the 7 TKIs showed PT-INR elevation, enhancement of the anticoagulation effect of WF in the presence of TKIs appears to be highly frequent. PT-INR should be carefully monitored, and adjusting the WF dosage may become necessary during the WF and TKI combination therapy.