Amoxicillin/clavulanic acid-warfarin drug interaction: a randomized controlled trial.

center dot Increased INR was previously observed in patients treated with warfarin and amoxicillin/clavulanic acid (amoxiclav) combination. To date, no prospective study has yet evaluated the effect of amoxiclav on INR in patients on warfarin therapy and consequently, there are no clear-cut conclusions or clear recommendations for clinicians. WHAT THIS PAPER ADDS center dot We provided the first systematic prospective evaluation of the interaction between amoxiclav and warfarin and found that amoxiclav did not modify INR in patients treated with stable warfarin therapy in the absence of any infectious or inflammatory syndrome, suggesting that the previously observed INR increase in these patients may not be attributable to a drug-drug interaction. AIMS To investigate whether an interaction exists between amoxicillin/clavulanic acid (amoxiclav) and warfarin in patients treated with stable oral anticoagulant therapy. METHODS In a double-blind, cross-over, placebo-controlled study, 12 patients on stable warfarin therapy, received a 7 day amoxiclav regimen or placebo. RESULTS The mean maximum increase in INR observed was 0.22 +/- 0.3 with amoxiclav vs. 0.24 +/- 0.6 with placebo (P = 0.94). The day 7-day 1 factor II, R(-) and S(-) warfarin plasma concentrations were similar during the amoxiclav and placebo study periods (P = 0.81, P = 0.45, P = 0.75, respectively). CONCLUSION Amoxiclav did not modify anticoagulation in patients treated with stable warfarin therapy and without infection.