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Warfarin induction at 5 mg daily is safe with a low risk of anticoagulant overdose: results of an audit of patients with deep vein thrombosis commencing warfarin

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Abstract Background: 

Conventionally warfarin therapy is initiated using a loading dose given over several days. Daily international normalised ratio (INR) monitoring is recommended to prevent overdose; however, with a large proportion of patients with deep vein thrombosis now receiving treatment out of hospital daily blood tests are inconvenient. We introduced a low-dose protocol for starting anticoagulant therapy that only required INR testing on days 4 and 6 and audited the results to assess safety and efficacy. Methods:

Two-hundred and forty-eight patients with confirmed deep vein thrombosis were started on warfarin therapy at 5 mg daily for 3 days. INR measurements were taken at day 4 and day 6. Results: 

Of these patients, 21% had an INR within the therapeutic range on day 4 and 52% had a therapeutic INR on day 6. The risk of overdose was small with only one case with an INR above 4.0 on day 4 and nine cases on day 6. There were no reported cases of bleeding. Conclusion:

The low-dose protocol with infrequent testing is safe and convenient for outpatient management. However, our results suggest that patients on this protocol take between 6–10 days to achieve a stable INR. (Intern Med J 2005; 35: 717–720)

Keywords: anticoagulation; deep vein thrombosis; venous thrombosis; warfarin

Document Type: Research Article


Affiliations: 1: Auckland Hospital, Auckland 2: Palmerston North Hospital, Palmerston North, New Zealand

Publication date: 2005-12-01

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