Warfarin Institute of America
DEDICATED TO YOUR HEALTH SINCE 2000
CIPROFLOXACIN INTERACTION WITH WARFARIN (Coumadin, Jantoven)
Brand Name: Cipro
This is a somewhat difficult interaction to predict. I have seen it happen quite a few times but I have also seen it not happen just about as often. Usually a person is taking warfarin (Coumadin, Jantoven), and ciprofloxacin is started. Sometimes the INR will become elevated and sometimes it will not. It might be related to how well the ciprofloxacin is absorbed. If someone absorbs it poorly and it destroys the bacteria in the intestinal tract the it could cause an elevated INR. But, it is just as likely that the INR is elevated because the person is sick and hasn't eaten well. The ciprofloxacin is then deemed guilty just because it was the new drug. In reality it might just have been an innocent bystander.
I think that the prudent thing to do is to have the INR checked three to five days after ciprofloxacin is started.
Since I originally wrote this page, I had the following exchange with a reader who suffered an adverse reaction even though this advice was followed.
"I have been taking warfarin for 6 years since my aortic valve was
replaced with a synthetic valve (St. Judes). Last year I developed a bad
gastric infection. After 3 weeks and several negative bacterial
screenings I was prescribed Cipro to see if it would help. The doctor
was aware of the possible interaction and therefore tested my INR 3 days
after starting treatment, just as you attest to doing. (I should also
say my IRN was tested 2 days prior to starting cipro, because that was
the normal testing date - it has been stable for many months and usually
is).
The post-cipro test INR was 9.7, which is hugely higher than my normal
3.0-3.5! Warfarin was therefore suspended, I was admitted to hospital
and the INR tested daily. The INR only reduced very slowly, and
unfortunately I suffered a major brain haemorrhage 4 days later - the
INR was still above 6.5 at that time."
"I do also appreciate that I was extremely unlucky to have such a bad
reaction between these drugs, but it does show it happens."
"In the meantime I am happy to add I am making a good overall recovery,
with only some memory difficulties and loss of eyesight (60% done)
remaining, and I am returning to work next week after 11.5 months off."
This personal experience certainly shows the importance of having the INR checked.
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Last modified May 7, 2006