Limited evidence on persistence with anticoagulants, and its effect on the risk of recurrence of venous thromboembolism: a systematic review of observational studies

The risk of venous thromboembolism (VTE) recurrence is high following an initial VTE event, and it persists over time. This recurrence risk decreases rapidly after starting with anticoagulation treatment and reduces by ~80%-90% with prolonged anticoagulation. Nonpersistence with anticoagulants could lead to increased risk of VTE recurrence. This systematic review aimed to estimate persistence at 3, 6, and 12 months with anticoagulants in patients with VTE, and to evaluate the risk of VTE recurrence in nonpersistent patients. PubMed and Embase(®) were searched up to May 3, 2014 and the search results updated to May 31, 2015. Studies involving patients with VTE aged ≥18 years, treatment with anticoagulants intended for at least 3 months or more, and reporting data for persistence were included. Proportions were transformed using Freeman-Tukey double arcsine transformation and pooled using the DerSimonian-Laird random-effects approach. In total, 12 observational studies (7/12 conference abstracts) were included in the review. All 12 studies either reported or provided data for persistence. The total number of patients meta-analyzed to estimate persistence at 3, 6, and 12 months was 71,969 patients, 58,940 patients, and 68,235 patients, respectively. The estimated persistence for 3, 6, and 12 months of therapy was 83% (95% confidence interval [CI], 78-87; I (2)=99.3%), 62% (95% CI, 58-66; I (2)=98.1%), and 31% (95% CI, 22-40; I (2)=99.8%), respectively. Only two studies reported the risk of VTE recurrence based on nonpersistence - one at 3 months and the other at 12 months. Limited evidence showed that persistence was suboptimal with an estimated 17% patients being nonpersistent with anticoagulants in the crucial first 3 months. Persistence declined over 6 and 12 months. Observational data on persistence with anticoagulation treatment, especially direct oral anticoagulants, in patients with VTE and its effect on risk of VTE recurrence were scarce and further research is required.