What is the recommended duration of antithrombotic therapy for a patient with a first episode of Deep Vein Thrombosis (DVT) of the lower limb, without specific comorbidities or risk factors?

Antithrombotic Therapy Duration for Lower Limb DVT

For a first episode of unprovoked proximal DVT in the lower limb, anticoagulation should be continued indefinitely (with no scheduled stop date) after the initial 3-month treatment period, provided the patient has low to moderate bleeding risk. 1, 2

Initial Treatment Phase (All Patients)

All patients with lower limb DVT require a minimum of 3 months of therapeutic anticoagulation to prevent thrombus extension and early recurrence, regardless of whether the DVT is provoked or unprovoked. 1, 3 This initial period addresses the acute thrombotic event, with 6 months offering lower early recurrence risk than 3 months. 1

• Preferred anticoagulant: Direct oral anticoagulants (DOACs) over warfarin for non-cancer patients 2
• Target INR for warfarin: 2.5 (range 2.0-3.0) if warfarin is used 4, 3
• Cancer patients: Low-molecular-weight heparin (LMWH) is preferred over DOACs or warfarin 2

Decision Algorithm After 3 Months

The critical decision point occurs at 3 months, and depends on two factors: whether the DVT was provoked or unprovoked, and the location of the thrombus (proximal vs. distal). 5, 1

Provoked DVT (Transient Risk Factor)

Stop anticoagulation at 3 months. 5, 2, 4

• Surgery-provoked DVT has an annual recurrence risk <1% after completing 3 months of treatment 5, 1
• Hormone-associated DVT in women should stop at 3 months if hormonal therapy is discontinued 5, 1
• Non-surgical transient risk factors have variable recurrence risk between surgical and unprovoked DVT, but generally stop at 3 months 5

Unprovoked Distal (Calf) DVT

Stop anticoagulation at 3 months. 5, 1

• Distal DVT confined to the calf (not extending into the popliteal vein) has a lower recurrence risk than proximal DVT 5
• Annual recurrence risk is approximately half that of proximal DVT 2
• Low risk of recurrent VTE presenting as PE 5, 1

Unprovoked Proximal DVT

Continue anticoagulation indefinitely after 3 months, with annual reassessment. 1, 2, 3

This recommendation is based on the annual recurrence risk exceeding 5% after stopping anticoagulation, which outweighs the bleeding risk in appropriately selected patients. 1, 2 The benefit of anticoagulation continues only as long as therapy is maintained. 1

Critical distinction: "Indefinite" means treatment with no scheduled stop date—this could be lifelong or until bleeding risk becomes prohibitive. 1 This is not a fixed time-limited period beyond 3 months. 1

Bleeding Risk Stratification

Bleeding risk must be formally assessed before committing to indefinite therapy. 1, 2

Low to Moderate Bleeding Risk (Suitable for Indefinite Therapy)

• Age <70 years 1, 2
• No previous major bleeding episodes 1, 2
• No concomitant antiplatelet therapy 1, 2
• No renal or hepatic impairment 1, 2
• Good medication adherence 1, 2

High Bleeding Risk (Stop at 3 Months)

• Age ≥80 years 1, 2
• Previous major bleeding 1, 2
• Recurrent falls 1, 2
• Need for dual antiplatelet therapy 1, 2
• Severe renal or hepatic impairment 1, 2

Important nuance: The FDA label for warfarin recommends 6-12 months for first unprovoked DVT 4, but the most recent high-quality guidelines from the American College of Chest Physicians and International Society on Thrombosis and Haemostasis support indefinite therapy due to the >5% annual recurrence risk. 1, 2 A 2025 meta-analysis confirmed that indefinite anticoagulation for unprovoked VTE reduces mortality (RR 0.54), recurrent PE (RR 0.25), and recurrent DVT (RR 0.15), despite increased bleeding risk (RR 1.98). 6

Ongoing Management for Indefinite Therapy

• Mandatory annual reassessment of bleeding risk factors, medication adherence, and patient preference 1
• Regular evaluation to determine if bleeding risk has become prohibitive 1
• The decision to continue must be actively reaffirmed, not passively continued 1

Critical Pitfalls to Avoid

• Do not treat all DVT the same: Failing to distinguish between proximal and distal DVT leads to inappropriate treatment duration 1
• Do not ignore provoked vs. unprovoked status: This is the strongest predictor of recurrence likelihood 1
• Do not use repeat imaging to guide duration: Treatment duration is determined by recurrence risk, not by whether the clot has disappeared on imaging 2
• Do not use fixed time-limited periods (e.g., 12 months) for unprovoked proximal DVT—guidelines recommend against this approach 1