Wow, excellent reply Angie O'Plasty! That's a good explanation about heparin acting faster and Coumadin slower. Many pt's ask why they are on both. Also I believe each medication affects a different end of the coagulation cascade (remember that from phys class?
In some facilities you will see a protocol or sliding scale to determine the daily Coumadin/warfarin dose. When I worked in a subacute nsg home, we had a paper printout, much just an insulin sliding scale. For example, if daily INR was 1.0, then give 5 mg Coumadin... if INR is 2, hold Coumadin today, etc... Where I work now, we have a computerized protocol. The computer pulls the daily INR lab results and determines what amount we should give at 1800. Sometimes the protocol tells us to call the physician for the amount.
While people are in the hospital, they usually have daily INR's. If people are on coumadin for chronic health problems such as stroke or afib like Angie said, then they will most likely go into their family clinic to have their INR's checked every couple of weeks or monthly or so.