Anticoagulation: reducing the loading dose of warfarin limited over anticoagulation.

Clinical bottom line (level 1b)

The same number of patients who started on 5 mg of warfarin had therapeutic INRs after 5 days as those who took 10 mg.
Fewer patients had an INR > 3.0 on day 4 in the 5 mg group (NNT = 4 at 4 days) .

Crowther et al: Thrombosis and Haemostasis 1997; : 583-583

Expires December 2003

The study

Unblinded ?concealed randomised trial with intention-to-treat
Setting: two university hospitals, Canada

102 patients (aged ?, ?% male) requiring anticoagulation (indications not given)
Control Group: (n = 46, 46 analysed): 10 mg warfarin loading dose, followed by doses based on nomogram
Experimental Group: (n = 56, 56 analysed): 5 mg warfarin loading dose, followed by doses based on nomogram

100% followed for 5 days INR measured daily

The evidence

Outcome	Time to outcome	CER	EER	RRR (95% CI)	ARR (95% CI)	NNT (95% CI)
INR 2.0 to 3.0	4 days	28 (60.9%)	40 (71.4%)	-17% (-56% to 12%)	-10.6% (-29.0% to 7.85%)	-9 (NNT = 13 to infinity; NNH = 3 to infinity)
INR 2.0 to 3.0	5 days	36 (78.3%)	44 (78.6%)	0% (-23% to 18%)	-0.31% (-16.4% to 15.7%)	-320 (NNT = 6 to infinity; NNH = 6 to infinity)
INR > 3.0	4 days	14 (30.4%)	2 (3.57%)	88% (51% to 97%)	26.9% (12.7% to 41.0%)	4 (2 to 8)

Comments

The information was taken from an abstract.
Does a lower loading dose affect long term recurrence of venous thromboembolism?

Citation

Crowther MA, Harrison L, Ginsberg JS, et al: A randomized comparison of a 5mg and 10 mg loading dose for the initiation of warfarin therapy. Thrombosis and Haemostasis 1997; : 583-583

Contributor: Chris Ball and Clare Wotton, December 2000
Reviewer:

_{Clinical Question.}

_Patient	_{requiring anticoagulation}
_{Intervention or Exposure}	_{5 mg warfarin}
_Comparison	_{10 mg}
_Outcome	_{therapeutic INR}