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Original ArticleOpen Access
The Efficacy of 3-mg Warfarin Initiating Dose in Adult Thai Patients, Who Required Long-Term Anticoagulant Therapy
Suwanawiboon B 
,
Kongtim P ,
Chinthammitr Y ,
Ruchutrakool T ,
Wanachiwanawin W
,
Kongtim P ,
Chinthammitr Y ,
Ruchutrakool T ,
Wanachiwanawin W Background: 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.
Objective: To investigate the efficacy and safety of 3-mg warfarin initiating dose.
Material and Method: 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.
Results: 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.
Conclusion: 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.
Keywords: Warfarin initiating dose, Warfarin loading dose, Efficacy, Time to therapeutic INR
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.
Objective: To investigate the efficacy and safety of 3-mg warfarin initiating dose.
Material and Method: 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.
Results: 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.
Conclusion: 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.
Keywords: Warfarin initiating dose, Warfarin loading dose, Efficacy, Time to therapeutic INR
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