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

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WHAT IS ALREADY KNOWN ABOUT THIS SUBJECTIncreased 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 ADDSWe 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.AIMSTo investigate whether an interaction exists between amoxicillin/clavulanic acid (amoxiclav) and warfarin in patients treated with stable oral anticoagulant therapy.METHODSIn a double-blind, cross-over, placebo-controlled study, 12 patients on stable warfarin therapy, received a 7 day amoxiclav regimen or placebo.RESULTSThe 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).CONCLUSIONAmoxiclav did not modify anticoagulation in patients treated with stable warfarin therapy and without infection.

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