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Table 5 Warfarin-related adverse events

From: Use of warfarin in long-term care: a systematic review

Study Study objective, (intervention/exposure and outcomes) Study design, data source Study population, study setting, time period Results Quality assessment, funding source
Gurwitz et al. (2007) [25] (repeated from Table 1)     720 warfarin-related AEs and 253 potential warfarin-related AEs were identified. Of the warfarin-related AEs, 87% were characterized as minor, 11% were deemed serious, and 2% were life-threatening or fatal. Overall, 29% of warfarin-related AEs were judged to be preventable. The rate of warfarin-related AEs was 18.8 per 100 resident-months on warfarin therapy (95% CI, 17.5-20.3 per 100 resident-months), with a rate of 5.4 preventable warfarin-related AEs per 100 resident-months (95% CI, 4.7-6.2 per 100 resident-months). Potential warfarin-related AEs occurred at a rate of 6.6 per 100 resident-months on warfarin (95% CI, 5.8-7.5 per 100 resident-months). Serious, life-threatening, or fatal events occurred at a rate of 2.5 per 100 resident-months (95% CI, 2.0-3.0 per 100 resident-months); 57% of these more severe AEs were considered preventable. Errors resulting in preventable AEs occurred most often at the prescribing and monitoring stages of warfarin management  
Quilliam et al. (2001) [26] To quantify the effect of antiplatelet and anticoagulant agents on risk of hospitalization for bleeding among an elderly nursing home stroke survivors Design: case- control study
Data source:
Medicare claims and MDS assessments in the SAGE database
Population: nursing home residents, 3433 cases (residents with first hospitalization for bleeds) and 13,506 controls (residents having no such hospitalizations)
Setting: nursing homes in5 states (US)
Time period: 1992-1997
After adjustment, use of warfarin (OR = 1.26; 95% CI = 1.11-1.43) and combination (antiplatelet and warfarin) therapy (OR = 1.34; 95% CI = 0.99-1.82) were associated with an increased risk of hospitalization for a bleed compared with nonusers. The odds of aspirin use was greater among cases than controls (OR, 1.07; 95% CI = 0.96-1.18) after adjustment. The numbers needed to treat to seriously harm (e.g. hospitalization for a bleed) 1 resident with aspirin and warfarin were 467 and 126, respectively. The odds of a CNS bleed with aspirin use was 1.36 (95% CI = 1.05-1.78) and 1.64 (95% CI = 1.19- 2.26) for warfarin use. The number needed to treat for harm values for CNS; bleeds were 534 (95% CI = 214- 3846) for aspirin and 301 (95% CI = 153-1012) for warfarin. Patients with GI bleeding were more likely to have taken warfarin (OR = 1.18; 95% CI = 1.03-1.36); number needed to treat for harm, 228 (95% CI = 114- 1366). Aspirin users were not more likely to be hospitalized for GI bleeds (OR = 1.01; 95% CI = 0.91- 1.14) Quality assessment for observational studies:
1) Unbiased selection of the cohort? Yes
2) Selection minimizes baseline differences in prognostic factors? Yes
3) Sample size calculated/5% difference? Yes
4) Adequate description of the cohort? Yes
5) Validated method for ascertaining exposure? Yes
6) Validated method for ascertaining clinical outcomes? Yes
7) Outcome assessment blind to exposure? Yes
8) Adequate follow-up period? Yes; cross-sectional
9) Completeness of follow-up? Yes
10) Analysis controls for confounding? Yes
11) Analytic methods appropriate? Yes
Funding: AHRQ
  1. AEs, adverse events; AHRQ, Agency for Healthcare Research and Quality; CI, confidence interval; OR, odds ratio; MDS, Minimum Data Set; SAGE, Systematic Assessment of Geriatric drug use via Epidemiology