Key result
Addition of ciprofloxacin to a stable warfarin regimen in a 72-year-old man increased prothrombin time from 15.5 seconds to 22 seconds after one week.
Why the study?
Does ciprofloxacin increase prothrombin time in patients taking warfarin?
Case Report (n=1)
Does ciprofloxacin increase prothrombin time in patients taking warfarin?
Absolute Event Rate: 22% vs 15.5%
Ciprofloxacin may interact with warfarin to increase prothrombin time, necessitating careful monitoring and potential dose adjustment.
Ciprofloxacin may require closer INR monitoring with warfarin; this case report leaves open confirmation in controlled studies.
A 72-year-old man had been taking warfarin for a pulmonary embolus and recurrent deep-vein thromboses. His prothrombin times (PTs) were maintained between 15 and 18 sec (PT ratio 1.25-1.5 x control) for several months on a dose of warfarin 2.5 mg/d. Six weeks prior to starting ciprofloxacin 500 mg bid, the patient's PT was 15.5 sec (Pt ratio 1.29 x control). After one week of ciprofloxacin, his PT had increased to 22 sec (PT ratio 1.83 x control). No other causes for the increase were apparent. It is recommended that patients receiving both medications have their prothrombin times carefully monitored and warfarin doses adjusted only as necessary.
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Alan K. Kamada (1990) conducted a case report in Pulmonary embolus and recurrent deep-vein thromboses (n=1). Ciprofloxacin vs. Baseline (warfarin alone) was evaluated on Prothrombin time (PT). Addition of ciprofloxacin to a stable warfarin regimen in a 72-year-old man increased prothrombin time from 15.5 seconds to 22 seconds after one week.