Time needed to bring the INR from 3 to 1.5

I have a patient 77 yrs age admitted  as an emergency with diagnosis of septic arthritis of the knee and shoulder and has to be operated as soon as possible. He has been on Coumadin for chronic atrial fibrilation and has an INR of 3.0

I want to revert his INR to 1.5 and would like to know how soon can I take him for arthroscopic surgery and what dose of Mephyton should I use, either p.o. or IV.

Please answer as soon as possible. Thank you.