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May 1, 1991

Adverse Reaction Reporting of Interaction Between Warfarin and Fluoroquinolones

Abstract

Reports to the Food and Drug Administration’s Adverse Drug Reaction Reporting System of prolonged prothrombin time due to a suspected interaction between warfarin sodium and a fluoroquinolone were reviewed. Five reports of patients who experienced this adverse reaction 2 to 16 days after the addition of a fluoroquinolone to their treatment regimen are described. Possible mechanisms of action that are discussed include inhibition of warfarin metabolism by the anti-infective agent and displacement of warfarin’s binding to protein. Physicians need to be aware of this interaction and closely monitor prothrombin time in patients concurrently receiving warfarin and a fluoroquinolone.

By Jolson HM, Tanner LA, Green L, Thaddeus H. Grasela

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