Warfarin (WF) has interactions with various drugs that alter its anticoagulant effect and this also applies to anti-cancer agents. However, interactions between WF and paclitaxel-carboplatin combination therapy (TC therapy) have not been adequately studied up till now. In view of this, we investigated such drug interactions in patients on WF who were receiving TC therapy at Kobe University Hospital from 1 February 2005 to 31 January 2010. As subjects, 17 patients in whom WF dosing had been stabilized prior to initiation of TC therapy were selected. Changes in the anticoagulant effect of WF due to TC therapy were investigated retrospectively. The pro-thrombin time international normalized ratio (PT-INR) significantly increased (from 2.00 to 2.58 (p <0.05)) after the initiation of TC therapy. However, this increase seemed to be transient. The PT-INR level peaked a few days after TC therapy, and then returned to normal within a few days. Furthermore, in patients who received additional concomitant drugs with known WF interactions, there was a tendency for PT-INR to increase even more than it did with TC therapy alone.
In the case of initiating TC therapy in patients taking WF, when analgesics or other drugs that are known to have interactions with WF are being given concomitantly, the anticoagulant effect will be increased significantly. Therefore, PT-INR should be closely monitored for a few days after TC therapy and patient education should be conducted before TC therapy is initiated in those on WF.
