title: Use of vitamin K antagonists and risk of subarachnoid haemorrhage: a population-based case-control study.
abstract: BACKGROUND
  Oral anticoagulant therapy with vitamin K antagonists is associated with an increased risk of bleeding, particularly gastrointestinal bleeding. It remains unclear, however, whether use of these medications is a risk factor for subarachnoid haemorrhage (SAH). We therefore examined the association between oral vitamin K antagonist use and risk of SAH.
  
  
  METHODS
  We conducted this population-based case-control study using medical databases in Northern Denmark (population 1,150,000). We identified 1188 patients admitted to neurologic or neurosurgical departments with a first-time diagnosis of SAH between 1996 and 2008 and 11,880 population controls. We obtained information on use of vitamin K antagonists, other medication use, and comorbidity. We used logistic regression analysis to compute odds ratios (ORs) comparing oral anticoagulant users and non-users, controlling for potential confounding factors.
  
  
  RESULTS
  9 cases (0.8%) and 157 controls (1.3%) were current users of vitamin K antagonists (at least one prescription filled within 90 days of the diagnosis/index date). Current use of vitamin K antagonists was not associated with increased SAH risk compared with non-use [adjusted OR=0.80 (95% CI: 0.37-1.74)]. Changing the exposure window from 90 days to 120 days or to 60 days before the diagnosis/index date did not change the estimate substantially.
  
  
  CONCLUSIONS
  We found no evidence to support an association between use of vitamin K antagonists and increased SAH risk.
authors.affiliation: Department of Clinical Epidemiology, Aarhus University Hospital, Olof Palmes Allé 43-45, Aarhus N, Denmark. mo@dce.au.dk
authors.forename: Morten
authors.initials: M
authors.lastname: Olsen
authors.forename: Martin Berg
authors.initials: MB
authors.lastname: Johansen
authors.forename: Steffen
authors.initials: S
authors.lastname: Christensen
authors.forename: Henrik Toft
authors.initials: HT
authors.lastname: Sørensen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000925:Anticoagulants / Q000009:adverse effects* / Q000627:therapeutic use; D016022:Case-Control Studies; D016001:Confidence Intervals; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D010644:Phenprocoumon / Q000009:adverse effects / Q000627:therapeutic use; D012307:Risk Factors; D013345:Subarachnoid Hemorrhage / Q000139:chemically induced*; D013923:Thromboembolism / Q000517:prevention & control; D014812:Vitamin K / Q000037:antagonists & inhibitors*; D014859:Warfarin / Q000009:adverse effects / Q000627:therapeutic use; D055815:Young Adult
chemical_list: D000925:Anticoagulants; D014812:Vitamin K; D014859:Warfarin; D010644:Phenprocoumon