Determination of Practical Dosing of Warfarin in Korean Outpatients with Mechanical Heart Valves / 대한흉부외과학회지

ABSTRACT

BACKGROUND: Following the implantation of heart valve prostheses, it is important to maintain therapeutic INR to reduce the risk of thromboembolism. The objective of this study was to suggest a practical dosing guideline for Korean outpatients with prosthetic heart valves managed by a pharmacist-run anticoagulation service (ACS). MATERIAL AND METHOD: A retrospective chart review was completed for all patients enrolled in the ACS at Seoul National University Hospital from March, 1997 to September, 2000. Patients who were at least 6 months post-valve replacement and had nontherapeutic INR value (less than 2.0 or greater than 3.0) were included. The data on 688 patients (1,782 visits) requiring dosing adjustment without any known drug or food interaction with warfarin were analyzed. The amount of adjusted dose and INR changes based on the INR at the time of the event were calculated. Aortic valve replacements (AVR) patients and mitral or double valve replacement (MVR/DVR) patients were evaluated separately. RESULT: Two methods for the warfarin dosage adjustment were suggested Guideline I (mg-based total weekly dose (TWD) adjustment), Guideline II (percentage-based TWD adjustment). The effectiveness of Guideline I was superior to Guideline II overall in patients with both AVR and MVR/DVR. CONCLUSION: The guideline suggested in this study could be useful when the dosage adjustment of warfarin is necessary in outpatients with mechanical heart valves.