Levofloxacin and warfarin interaction
Abstract
OBJECTIVE: To report 4 cases of hypoprothrombotic response resulting from addition of levofloxacin therapy to chronic warfarin therapy and to review related literature to support or refute a warfarin-levofloxacin interaction. CASE SUMMARY: Four patients, 34-81 years old, were prescribed levofloxacin concomitantly with stable warfarin therapy. Three patients had a target international normalized ratio (INR) range of 2.0-3.0 and experienced an increase in INR to 3.5, 8.12, and 11.5 on days 11, 5, and 4 of a 10-day course of levofloxacin, respectively. The fourth patient experienced minor bleeding, with a slightly elevated INR on the second day of levofloxacin therapy that required up to a 19% warfarin dose reduction during levofloxacin treatment. DISCUSSION: An initial premarketing clinical trial concluded that levofloxacin had no effect on warfarin's pharmacokinetics and pharmacodynamic response. Two case reports have since documented an increase in INR in patients taking long-term warfarin on completion of levofloxacin therapy. Our case reports provide further evidence of a significant increase in INR observed during concomitant levofloxacin therapy. The proposed mechanism of this interaction is displacement of warfarin from protein binding sites, reduction in gut flora producing vitamin K, and decreased warfarin metabolism. CONCLUSIONS: Prolonged prothrombin response in patients undergoing chronic warfarin therapy has been well documented with many antibiotics, including…
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