Hi little flower, welcome and thanks for your question. Do you have a hematologist that you could talk to about your question? I have no idea if Fosteum would endanger an INR level or if coumadin is contraindicated with Fosteum. I would either talk to your Dr., the one rx-ing the Fosteum, a hematologist or your pharmacist.
Fosteum has genistein (isoflavone isolated from soy) zinc and D3 in it. Does the package insert say anything about these ingredients with regard to atrial fib, INR or blood clots?
Sorry I couldn't help but your Dr. should be able to give you this information.