Recommendations for oral anticoagulant (OAC) therapy in deep vein thrombosis (DVT) are as follows53:
- For patients with a first episode of DVT secondary to a reversible risk factor, long-term treatment with vitamin K antagonists (VKAs) for 3 months is recommended (Grade 1A)
- For patients with a first episode of idiopathic DVT, treatment with VKAs for at least 6 to 12 months is recommended (Grade 1A).
- For patients with DVT and cancer, low-molecular weight heparin is recommended for the first 3 to 6 months of long-term anticoagulant therapy (Grade 1A). For these patients, anticoagulation is recommended indefinitely or until the cancer is resolved.
- For patients with a first episode of DVT and documented antiphospholipid syndrome or who have two or more thrombophilic risk factors (e.g. combined factor V Leiden and prothrombin 20210 gene mutations), treatment for 12 months is recommended (Grade 1C). Indefinite anticoagulant therapy is also recommended in these patients.
- For patients with a first episode of DVT who have documented deficiency of antithrombin, protein C or protein S, or the factor V Leiden or prothrombin 20210 gene mutation, homocysteinemia, or high factor VIII levels (>90th percentile), treatment for 6 to 12 months is recommended (Grade 1A). Indefinite therapy is recommended, as for patients with idiopathic thrombosis (Grade 2C).
- For patients with two or more episodes of objectively documented DVT, indefinite treatment is suggested (Grade 2A).
- It is recommended that the VKA dose be adjusted to maintain a target international normalized ratio (INR) of 2.5 (2.0–3.0) for all treatment durations (Grade 1A). The guidelines recommend against high-intensity VKA therapy (3.1–4.0) (Grade 1A) and against low-intensity therapy (INR range, 1.5–1.9) compared to INR range of 2.0 to 3.0 (Grade 1A).
- In patients who receive indefinite anticoagulant treatment, the risk‐benefit of continuing such treatment should be reassessed at periodic intervals (Grade 1C).
- Repeat testing with Doppler ultrasound is suggested to exclude residual thrombosis or measurement of plasma D-dimers, to help determine the duration of the treatment (Grade 2C).