Amoxicillin and Warfarin

Hello I take 6.5 mg of warfarin and 2.5 mg of bisoprolol each day my INR range has to be between 2 to 3

I am currently in AF since Friday

Been to the doctors this morning

He said an infection could of triggered it off so he has increased my bisoprolol to

5 mg each day and put me on a course of antibiotics Amoxicillin 500 mg

I go for an INR test in 10 days time

Does anyone know

Will there be any interactions involving antibiotics and warfarin.

9 Replies

  • Yes usually increases INR - my surgery booked me in for an early test 3 days after starting a course of antibiotics.


  • The antibios will affect INR so an extra test would be sensible. If it is a seven day course then at ten days you should be back to normal so good time to test but one at three or four days could re-assure you.

    To be honest I am concerned that you don't say if you do have an infection of some sort or if the GP has just taken a punt which seems highly irresponsible knowing the problems of antibiotic resistant bugs. Have you been unwell or is it just that you are in AF?

  • Yes I said I had a bad cough , light headed and not feeling well

    He checked me and said my lungs were clear.

  • Oh Dear. One of those GPs. There was a big trans European study last year regarding coughs and antibiotics and unless you have fluid on your lungs you will get better with or without antibiotics. In a few years we will not have any antibios which work at this rate. Scary or what!

  • Totally agree Bob

  • Yes there are with some antibiotics. When the GP said about amoxicillin did you say something to the effect that I suffer from AF and I am on warfarin? If not check with your pharmacist. Another resource is which is an American site. The vast majority of the things are the same but a few are different. A few months back I was given an antibiotic for swollen hand because of hitting my knuckle and GP said prescribing this one because of your heart problems.

  • Hit send to soon. Extra INR test 4 days in and then your 11 days then possibly 1 week after that. Make sure Anticoagulation specialist knows you are on antibiotics and tell them the actual dose.

  • Yes the main reason I went to see him was that I was in AF

  • I've had two courses of antibiotics in the last 6 weeks - the last one being amoxicillin (which did nothing for my infected bronchials but made me feel awful!). Had an INR check 10 days after both courses and there was no change at all. Still best to check, just in case.

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