Key result
Initiation of simvastatin among warfarin users led to a minor increase in mean INR of 0.32 (95% CI 0.25-0.38), with similar minor increases observed for atorvastatin and rosuvastatin.
Why the study?
Initiation of statins is suggested to increase INR among warfarin users, but available data are limited and conflicting.
Does initiation of simvastatin, atorvastatin, or rosuvastatin increase INR in warfarin users?
Cohort (n=1,551)
Does initiation of simvastatin, atorvastatin, or rosuvastatin increase INR in warfarin users?
Mean Difference: 0.32 (95% CI 0.25–0.38)
Absolute Event Rate: 2.71% vs 2.4%
Initiation of statins in warfarin users leads to a minor, likely clinically insignificant increase in INR.
Minor INR increases with statin initiation in warfarin users appear clinically insignificant; observational data leaves open need for randomized confirmation.
Initiation of statin treatment is suggested to increase the international normalised ratio (INR) among warfarin users. However, available data is limited and conflicting. We conducted a register-based cohort study to evaluate the drug-drug interaction between warfarin and statins. By linking data on INR measurements and filled prescriptions, we identified warfarin users 2000-2015 initiating simvastatin (n = 1363), atorvastatin (n = 165) or rosuvastatin (n = 23). Simvastatin initiation led to an increase in mean INR from 2.40 to 2.71, with INRs peaking after 4 weeks, corresponding to a mean change of 0.32 (95%CI 0.25-0.38). High-dose and low-dose simvastatin led to comparable changes (mean change 0.33 vs 0.29). Initiation of atorvastatin and rosuvastatin lead to INR increases of 0.27 (95%CI 0.12-0.42) and 0.30 (95%CI -0.09-0.69). In conclusion, initiation of simvastatin, atorvastatin or rosuvastatin among warfarin users led to a minor increase in INR. The magnitude of this change is for most patients likely of limited clinical relevance.
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Engell et al. (2020) conducted a cohort in Warfarin users (n=1,551). Statin initiation (simvastatin, atorvastatin, rosuvastatin) vs. Baseline (prior to statin initiation) was evaluated on Change in mean INR (MD 0.32, 95% CI 0.25-0.38). Initiation of simvastatin among warfarin users led to a minor increase in mean INR of 0.32 (95% CI 0.25-0.38), with similar minor increases observed for atorvastatin and rosuvastatin.
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