Prevention

• See anticoagulation chapter for more details on warfarin therapy.

• It reduces the risk of stroke, but causes more major bleeds than placebo ^a
• It prevents more strokes than aspirin ^a , but causes more major bleeds ^a .  There is no clear effect on mortality. ^a
• Warfarin is more cost-effective than aspirin at preventing stroke in elderly patients with one or more risk factors for stroke. ^a
• Low-dose or fixed-dose warfarin is not clearly as effective as adjusted-dose warfarin. ^a
• Patients with AF on warfarin are at increased risk for a stroke, TIA or a major bleed if their INR is 4.0 or more. ^b

Adjusted-dose warfarin reduces stroke and death, but increases the risk of major bleeds

Patient	Treatment	Comparison	Outcome	CER	OR (95% CI)	NNT (95% CI)
AF a	adjusted-dose warfarin	placebo	stroke at 1.6 years	9.2%	0.38 (0.28 to 0.52)	18 (16 to 24)
			death at 1.6 years	9.2%	0.74 (0.57 to 0.96)	63 ( to )
			major extracranial bleed at 1.6 years	9.2%	2.4 (1.2 to 4.6)	-33 ( to )
	adjusted-dose warfarin	aspirin	stroke at 2.2 years	8.7%	0.64 (0.40 to 0.73)	34 (20 to 46)

Warfarin causes more major bleeds than aspirin

Patient	Treatment	Comparison	Outcome	CER	RRR (95% CI)	NNH (95% CI)
AF a	warfarin	aspirin	major bleed at 2.6 years	2.9%	-110% (-270% to -17%)	31 (18 to 140)

Adjusted-dose warfarin prevents more strokes than fixed-dose warfarin and aspirin

Patient	Treatment	Comparison	Outcome	CER	RRR (95% CI)	NNH (95% CI)
AF a	adjusted-dose warfarin	fixed-dose warfarin and aspirin	ischaemic stroke or systemic emboli at 12 months	2.1%	-300% (-670% to -110%)	16 (11 to 27)