AF Association
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Antibiotics v. Warfarin

Can anyone please tell me if there is a "safe" antibiotic one can take alongside Warfarin, or if there is one which does not affect ones INR.

I am unable to take an antibiotic containing any trace of penicillin as I am highly allergic to it and when I spoke to my pharmacist about this he checked his bible of pills and potions, and it showed all other antibiotics seriously conflict with Warfarin. I am now very worried that if I should require an antibiotic in the future - near or far - I would not be prescribed one. Either that or I will have to come off Warfarin and to me that seems equally as dangerous.

8 Replies

No this is not what happens. Most antibiotics affect your INR if you are on warfarin so it is usual to have to have extra INR tests every few days. or after a week of antibios just to make sure you haven't gone over the top. It really isn't a case of stopping anything. just better control.

Relax it may never happen.


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I was given Nitrofurantoin - not sure how specific/general or effective it is. I'd never heard of it before.




Hi Langara. Like you, I am seriously allergic to penicillin. I am given Erythromycin 500mg tablets on the rare occasion I need an antibiotic. It doesn't seem to cause any problems and I have been on Warfarin for 28 years. The ideal is to let your Warfarin clinic know if you take anything new so that they can allow for it in assessing your dosage.mind you that goes for other things as well. Pigging out on smoke salmon or gorgonzola cheese sends my INR somewhat haywire!!


Thank you everyone. It is so comforting to have this site and to learn of all your experiences.


Can't take penicillin either , nor erythromicin. Clindamycin is a big no. I can take the Cephalosporins though. I think that all of the antibiotics require a close watch on your INR levels.e. Sandra


Thank you Sandra.


Hi Langara I just stop my warfarin on the second day of antibiotics just for one day and have weekley blood test after normaley works out fine.


Thank you - I will bear that in mind.


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