A retrospective cohort study in the Annals of Pharmacotherapy found a clinically significant decrease in warfarin dose-response with concurrent hepatitis C treatments, especially with ombitasvir/paritaprevir/ritonavir and dasabuvir (OBV-PTV/r-DSV). 

Douglas DeCarolis, PharmD, from the Minneapolis VA Health Care System, Minneapolis, MN, and colleagues conducted a study to determine if a drug interaction occurs when hepatitis C virus (HCV) treatments are added to warfarin. 

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Using the Veterans Affairs Health System database, study authors identified patients taking warfarin and treated with sofosbuvir or OBV-PTV/r-DSV between March 2014 to October 2015. The primary outcome was the change in warfarin sensitivity index (WSI) — defined as the steady-state INR divided by the mean daily warfarin dose — from HCV treatment initiation to completion.

The analysis, which included 271 patients, showed a 23% decrease in WSI from 0.53 to 0.39 (decrease 0.14, 95% CI: 0.11–0.16; P<0.001). Compared to any sofosbuvir regimen, OBV-PTV/r-DSV resulted in a significantly greater WSI decrease. The concurrent ribavirin accounted for an additional reduction in warfarin sensitivity of –0.09 (95% CI: –0.06 to -0.12; P<0.001). There was also an increase in the percent of subtherapeutic INR results from prior to HCV treatment to during treatment (26% to 58%).

Dr. DeCarolis and team concluded that OBV-PTV/r-DSV demonstrated the most pronounced effect on warfarin therapy; ribavirin was associated with an additive effect. Healthcare professionals should be aware of this potential drug interaction to carefully observe and minimize subtherapeutic anticoagulation levels. 

For more information visit aop.sagepub.com.