Abstract
With warfarin there are many factors that reduce or enhance the anticoagulant effect. We retrospectively studied the risk factors of prolongation of International Normalized Ratio (PT-INR) of prothrombin time for patients receiving warfarin by the pharmacoepidemiological method.
We targeted patients whose PT-INR was 4.5 or more from a review of medical charts. For each of these patients, we selected two control patients who were matched in terms of age (±5 years), sex, duration of taking warfarin, diagnosis and department prescribing the warfarin. We compared patient backgrounds, clinical laboratory test result and the concomitant drugs prescribed between the cases and the controls.
Of the 740 patients taking warfarin during the investigation period, 39 (5.27%) had a PT-INR of 4.5 or more and were selected as the cases. Between the cases and the controls, no statistically significant differences were seen in dosage, duration of taking warfarin, or prescribing reason. In the case group, serum albumin levels were significantly lower than in the control group (P<0.05). The drug amiodarone was a significant risk factor for PT-INR prolongation with an odds ratio of 11.32 (95% confidence interval 1.27-100.64).
Thus, low serum albumin and concomitant administration of amiodarone were significant risk factors for PT-INR prolongation.
