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.
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.


CONCLUSIONS
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.
Harper
P
P
Auckland Hospital, Auckland, New Zealand. paulh@adhb.govt.nz
Monahan
K
K
Baker
B
B
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000008:administration & dosage*; D002648:Child; D062787:Drug Overdose / Q000517:prevention & control; D005260:Female; D006801:Humans; D019934:International Normalized Ratio; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D020246:Venous Thrombosis / Q000188:drug therapy*; D014859:Warfarin / Q000008:administration & dosage*
D000925:Anticoagulants; D014859:Warfarin