Why the study?
Does the addition of a fluoroquinolone to warfarin therapy cause prolonged prothrombin time?
Does the addition of a fluoroquinolone to warfarin therapy cause prolonged prothrombin time?
Concurrent use of warfarin and fluoroquinolones may lead to prolonged prothrombin time, requiring close monitoring.
Potential interaction warrants INR monitoring with concurrent use; case reports leave open need for prospective validation.
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.
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Heidi M. Jolson (1991) studied this question.