The efficacy of 3-mg warfarin initiating dose in adult Thai patients, who required long-term anticoagulant therapy.

Warfarin anticoagulation is the standard treatment for patients with thromboembolic diseases. Prior studies recommended commencing warfarin with the initial doses between 5 mg and 10 mg for the first 1 or 2 days. However, lower warfarin loading dose is advised for the elderly and patients with co-morbid diseases. Moreover, warfarin requirement is also affected by several genetic factors, which differ among various ethnic populations. Currently, the optimal initiating dose of warfarin in Thai patients is unknown. However, based on the observation of the clinical practice at Siriraj hospital, a lower starting dose (3 mg/day) of warfarin was commonly given to patients who required long-term anticoagulant therapy.To investigate the efficacy and safety of 3-mg warfarin initiating dose.A retrospective study of inpatients who received warfarin 3 mg/day for the first two days of oral anticoagulation therapy with the target INR of 2.0-3.0 at Siriraj hospital from January 2004-December 2007 was performed. The efficacy of 3-mg warfarin loading dose was determined by assessing the proportion of patients who achieved the target INR of 2.0-3.0 between day 3 and day 5 of warfarin treatment.Total of 164 patients was included in the study. Eighty-six patients (52.4%) were males. The mean age was 55.1 + 16.8 years (range 16-88 years). The mean body weight and serum albumin were 61.5 +/- 12.2 kg and 3.7 +/- 0.7 g/dl, respectively. Prosthetic heart valve replacement was the most common indication for warfarin anticoagulation therapy (36%), followed by deep vein thrombosis (32.3%). The mean cumulative weekly dose of warfarin was 22.3 +/- 5.8 mg. The median time to therapeutic INR (2.0-3.0) was 6 days. Forty-seven patients (29%) achieved therapeutic INR between day 3 and day 5 of warfarin treatment. Time to therapeutic INR was not affected by age, gender, body weight, serum albumin, or concomitant medication use. Interestingly, patients who received warfarin due to prosthetic heart valve replacement were more likely to achieve therapeutic INR between day 3 and day 5 when compared to those with other indications with adjusted OR 16.25 (95% CI 5.13-51.44, p < 0.001). Bleeding complication was rare (0.6%) and was not associated with excessive anticoagulation.3-mg warfarin initiating dose appeared to be safe in adult Thai patients. However, the efficacy of 3-mg starting dose as determined by the proportion of patients who achieved the target INR between day 3 and day 5 of warfarin treatment was relatively less efficient when compared with that previously reported with a 5-mg loading dose. Further randomized, prospective study is required to examine the efficacy of 3-mg versus higher warfarin starting dose in Thai patients.