The incidence of recurrent venous thromboembolism after treatment with vitamin K antagonists in relation to time since first event: a meta-analysis.
BACKGROUND
After a first episode of venous thromboembolism, patients are treated with vitamin K (phytonadione) antagonists. There are indications that the risk of recurrence after treatment with vitamin K antagonists decreases relative to the time since the first event. The aim of the present meta-analysis is to describe the risk of recurrent venous thromboembolism after treatment with vitamin K antagonist in relation to the time since the index event.


METHODS
Computerized searches in MEDLINE and EMBASE databases; reference checks of pertinent articles; personal communication with colleagues to find randomized clinical trials and cohort studies in which patients with venous thromboembolism were treated with vitamin K antagonists. Per treatment arm, 2 reviewers independently extracted data on the number of recurrent events and the duration of follow-up per time period of 3 months.


RESULTS
A total of 135 potentially eligible studies were identified. Of these, 18 studies could be included, comprising 25 treatment arms that could be analyzed. Treatment arms were divided into 3 groups based on treatment duration (short, medium, and long). For all 3 groups, the monthly incidence immediately after discontinuation of treatment was high and declined rapidly thereafter. The monthly incidence after 9 months seemed independent of the treatment duration.


CONCLUSIONS
There is a diminishing risk of recurrent venous thromboembolism over time and a stabilization after 9 months independent of the duration of the initial treatment with vitamin K antagonists. These findings have important implications for decision making about the optimal duration of treatment with vitamin K antagonists.
van Dongen
Carlo J J
CJ
Department of Clinical Epidemiology, Academic Medical Center, Amsterdam, The Netherlands. c.j.vandongen@amc.uva.nl
Vink
Roel
R
Hutten
Barbara A
BA
Büller
Harry R
HR
Prins
Martin H
MH
D000925:Anticoagulants / Q000008:administration & dosage* / Q000009:adverse effects; D006801:Humans; D011655:Pulmonary Embolism / Q000517:prevention & control; D012008:Recurrence; D012307:Risk Factors; D013997:Time Factors; D020246:Venous Thrombosis / Q000517:prevention & control*; D014812:Vitamin K / Q000037:antagonists & inhibitors*
D000925:Anticoagulants; D014812:Vitamin K