オキシコドン併用がワルファリン服用がん患者のプロトロンビン時間に及ぼす影響

Abstract

The anticoagulant drug warfarin is used to prevent conditions such as venous thrombosis and so on. Since warfarin has many interactions with other drugs and a large inter-individual pharmacodynamic variability, its dosage must be adjusted based on the prothrombin time international normalized ratio (PT-INR) in each patient. Oxycodone is often used to control cancer pain. In the drug package insert, care should be taken when co-administering oxycodone with warfarin, but the mechanism of the interaction between the two remains unknown. In addition, there have been no reports on interaction between oxycodone and warfarin in patients.In this study, we retrospectively investigated the effect of oxycodone on the blood coagulation activity in 9 cancer patients who were treated with warfarin. After combination with oxycodone, the total dosage of warfarin in two weeks was significantly decreased to 78.6% of that without oxycodone. The median of PT-INR was also significantly increased from 2.03 to 2.30 compared to that without oxycodone. Moreover, the median of the warfarin sensitivity index, which was defined as PT-INR/warfarin dose (mg/day), was also significantly increased from 0.78 to 0.96 after coadministration with oxycodone.These results suggest that the anticoagulant effect of warfarin was increased after the co-administration of oxycodone in cancer patients treated with warfarin. Therefore, PT-INR should be frequently monitored after the start of co-administration of oxycodone.