Key result
Initiation of simvastatin in patients on warfarin therapy increased the proportion of patients with an INR above 3 from 8% to 15% and resulted in a 6.8% decrease in warfarin dose requirements.
Why the study?
Evidence was scarce on whether simvastatin increases the anticoagulative effect in patients treated with warfarin.
Does simvastatin initiation increase INR and reduce warfarin dose requirements in patients on ongoing warfarin therapy?
Cohort (n=5,637)
Does simvastatin initiation increase INR and reduce warfarin dose requirements in patients on ongoing warfarin therapy?
Absolute Event Rate: 15% vs 8%
Initiation of simvastatin in patients on warfarin leads to a moderate increase in INR and a subsequent need for warfarin dose reduction, highlighting the need for closer INR monitoring.
May warrant closer INR monitoring after simvastatin initiation in warfarin users; extends observational data but leaves causal effects open.
PURPOSE: Some data indicate that simvastatin may increase the anticoagulative effect in patients treated with warfarin, but the evidence is scarce. The aim of the present study was to investigate how the anticoagulative effect of warfarin is affected by the initiation of simvastatin in a very large patient sample. METHODS: In a retrospective cohort study, we included 5637 individuals on warfarin treatment initiating simvastatin. INR values and warfarin doses were calculated week-by-week during co-treatment. Data were obtained from two large Swedish warfarin registers and from the Swedish Prescribed Drug Register. RESULTS: INR increased from 2.43 at baseline to 2.58, 4 weeks after simvastatin initiation, and did not stabilize until the last quarter of the year studied. Consequently, the proportion of patients with an INR above 3 increased from around 8 to 15%. CONCLUSIONS: In conclusion, initiation of simvastatin resulted in moderately increased INR values and subsequent dose decreases in patients already on warfarin. In order to avoid the increased risk of bleeding, the initiation of simvastatin may be accompanied by closer INR monitoring.
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Andersson et al. (2019) conducted a cohort in Patients on warfarin treatment initiating simvastatin (n=5,637). Simvastatin initiation vs. Baseline (prior to simvastatin initiation) was evaluated on Proportion of patients with an INR above 3. Initiation of simvastatin in patients on warfarin therapy increased the proportion of patients with an INR above 3 from 8% to 15% and resulted in a 6.8% decrease in warfarin dose requirements.
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