Paxlovid and warfarin interaction

Paxlovid is the current leading anti-viral being used to treat COVID. For those of us on warfarin, please be aware that Paxlovid affects the clearance of warfarin and can have the effect of either increasing or decreasing INR.

If you happen to be prescribed Paxlovid, please monitor your INR closely so that adjustments can be made if needed in a timely manner. This is a good policy for any new medication or supplement being introduced.

See info linked below:


“Anticoagulants, or blood thinners used to treat or prevent blood clots, such as warfarin may be co-administered with Paxlovid but require close monitoring of clotting factors in bloodwork. The plasma levels of all direct oral anticoagulants increase when co-administered with Paxlovid, therefore dose adjustment or temporary discontinuation and use of alternative anticoagulants may be required.”

https://www.acc.org/Latest-in-Cardi...hinners used,of clotting factors in bloodwork

Impact of Paxlovid on international normalized ratio among patients on chronic warfarin therapy

I've got a little anecdotal data from my own situation to report.

I tested positive for Covid with a home antigen test yesterday morning. Very faint line on the lateral test, which usually indicates that you are at the beginning of the infection or near the end, as the line is most prominent when the virus is at max strength. Test repeated, same results.

I called my local clinic and got a prescription for Paxlovid. Before taking I read up on it, and learned that it is a CYP450 inhibitor and is known to interfere with the clearance of warfarin. So, I decided I would watch INR during the 10 day course of the antiviral.

Baseline INR 5/29
(before going on Paxlovid) 2.6

INR 5/30
(after 24 hours on Paxlovid) 2.5

So, essentially no change and no change needed to my warfarin dosage.

Also, I tested negative for Covid today. This would seem to indicate that yesterday when I got the faint line indicating that I was positive, that I was at the tail end of my infection and not at the beginning. Paxlovid is only effective if taken within 5 days of contracting Covid, and it appears that I am probably beyond that. So, I will probably discontinue the Paxlovid. Perhaps I'll test again soon to confirm before deciding to discontinue.