Antibiotic use as a marker of acute infection and risk of first and recurrent venous thrombosis

Summary A role for transient infections in the aetiology of venous thrombosis ( VT ) has been suggested. This study aimed to determine whether individuals who receive antibiotic treatment (as a proxy for infections) have an increased risk of first and recurrent VT and whether infections should be seen as a provoking risk factor for VT . We used the self‐controlled case series method to study the risk of first VT during antibiotic prescriptions. The risk of recurrent VT during antibiotic use was estimated by of time‐dependent Cox‐regression. A total of 2547 patients with a first VT were included and followed for a median of 5·9 years for recurrence (1999–2010), in whom 114 first events occurred during antibiotic use. We found a five‐fold increased risk of first VT during antibiotic treatment: [incidence‐rate‐ratio 5·0; 95% confidence interval ( CI ), 4·0–6·1]. Antibiotic use was associated with a 2·0‐fold (95% CI , 1·1–4·0) increased risk of recurrent VT . Patients with an unprovoked first VT who used antibiotics shortly before this event, had a similar risk of recurrence as patients with a provoked first VT (adjusted hazard ratio 1·1; 95% CI , 0·7–1·7). Individuals who receive antibiotics have an increased risk of first and recurrent VT and infections should be considered a provoking risk factor for VT .