Effect of Warfarin after Heart Valve Surgery in Lampang Hospital, Thailand - การติดตามผลการรักษาด้วยยาวาร์ฟาริน ในผู้ป่วยผ่าตัดลิ้นหัวใจ โรงพยาบาลลำปาง

บทคัดย่อ

            Warfarin is an oral anticoagulant that is widely used in several indications, including heart valve surgery. According to its pharmacokinetic, anticoagulant effect of warfarin is fully effective in five to seven days. However for heart valve surgery at Lampang Hospital, patients were monitored for the anticoagulant effect of warfarin using the International Normalized Ratio (INR) after three days of prescribing warfarin to detect the response of patients to warfarin. The study was conducted to see how many patients had extreme response and to evaluate the associated factors. It was conducted as a cross sectional analytical study carried out on patients who had undergone heart valve surgery and had received warfarin therapy at
Lampang Hospital from October 2012 to September 2013. Patients’ characteristics data, warfarin dosing and INR value were collected. INR value at day three was used to classify patients as slow response (INR<1.6), normal response (INR 1.6-2) or extreme response (INR>2). Patient characteristics data were analyzed using descriptive statistics and factors associated were analyzed using inferential statistics including Fisher’s exact probability test, one-way anova and Multinomial logistic regression. As for the results, 182 patients were included: 52.8% were male with an average age of 52.5±11.8 years. Among them, 52.8% had never used warfarin before surgery. The average initial dose was 1.9±0.5 mg/day. According
to the INR on day three for patients prescribed warfarin, 49.4% had slow response, 19.8% had normal response and 30.8% had extreme response. From multivariate logistic regression analysis when adjusted with gender, age, history of warfarin used, initial dose, INR at baseline and concomitant with amiodarone and using slow response patients as a baseline, the result revealed that factors associated warfarin overresponse significantly (p<0.05) were female (OR=2.7, CI 1.2-6.0), age over 60 years (OR=8.6, CI 3.2-23.2), new user (OR=5.9, CI 2.4-14.5) and initial dose over 2 mg/day (OR=4.3, CI 1.6-11.8). The authors concluded that around one third of patients who underwent heart valve surgery at Lampang Hospital had an over-response to warfarin three days after starting on it. In order to prevent a warfarin overdose in such patients we should closely monitor female patients, patients over the age of 60 and new warfarin users who are given a dose of over 2mg/day of warfarin.
Key words: heart valve surgery, warfarin, international normalized ratio (INR)