Therapy

• for 6 weeks for transient risk factors (e.g. surgery, recently bed-ridden) ^a
• for 6 months for permanent risk factors (e.g. cancer, leg paralysis) ^{a d}
• indefinitely for idiopathic cases ^{a d} or recurrent venous thromboembolism ^a

• Patients with venous thromboembolism who take vitamin K antagonists for longer periods compared with shorter are less likely to have another episode, but are more likely to have a major bleed. ^a
• Six months of anticoagulation is not clearly better than six weeks for patients with temporary risk factors (e.g. surgery, trauma, plaster-casts). ^a
• Patients with permanent risk factors at increased risk for recurrent VTE compared to patients with transient risk factors. ^c Six months of anticoagulation leads to fewer recurrent episodes of venous thromboembolism in patients with permanent risk factors (e.g. cancer, thrombophilia, paresis) than six weeks. The effect on mortality and major haemorrhage is unclear. ^a
• Indefinite oral anticoagulant therapy for a first idiopathic episode of a DVT or PE leads to fewer recurrences of venous thromboembolism than 3 months of therapy without clearly increasing bleeding or mortality. ^a
• Indefinite oral anticoagulant therapy for a second episode of a DVT or PE leads to fewer recurrent venous thromboembolism than 6 months of therapy without clearly increasing mortality. ^a

Longer duration of anticoagulation reduces recurrent venous thromboembolism but increases the risk of bleeding.

Patient	Treatment	Comparison	Outcome	CER	OR (95% CI)	NNT (95% CI)
first PE or DVT a	longer duration of anticoagulation	shorter duration of anticoagulation	recurrent venous thromboembolism at 2 years	20%	0.37 (0.28 to 0.51)	9 (8 to 12)
			major bleeding at 2 years	0.54%	3.75 (1.63 to 8.62)	-69 (-300 to -25)

Indefinite anticoagulation reduces recurrent venous thromboembolism for idiopathic or recurrent episodes

Patient	Treatment	Comparison	Outcome	CER	RRR (95% CI)	NNT (95% CI)
first PE or DVT a	anticoagulation for 6 months	anticoagulation for 6 weeks	recurrent venous thromboembolism at 2 years	18%	48% (26% to 63%)	12 (8 to 24)
first idiopathic PE or DVT a	indefinite anticoagulation	anticoagulation for 3 months	recurrent venous thromboembolism at 10 months	21%	94% (55% to 99%)	5 (4 to 10)
second PE or DVT a	indefinite anticoagulation	anticoagulation for 6 months	recurrent venous thromboembolism at 4 years	21%	88% (60% to 96%)	6 (4 to 10)