Heparin should be given for no less than 5 days and only discontinued at that time if the INR is therapeutic for 24 hours. Warfarin may be initiated on the first or second day of heparin therapy. Because factor II and X levels require at least 5 days to decline sufficiently, parenteral anticoagulation should overlap with warfarin for at least 5 days and until an INR of 2 or more is achieved.

The initial warfarin dose may be based on a patient's predicted maintenance dose using available calculators, and a patient's nutritional status, comorbid diseases, and age must be considered. Excessively high initial doses should be avoided because they can lead to supratherapeutic INR values and premature discontinuation of parenteral therapy. Patients should be followed closely with frequent INR studies at the initiation of therapy to achieve values consistently within the desired range. After patients achieve consistently stable INR levels with an established dose, INR monitoring may eventually be extended to every 12 weeks for the duration of treatment, but testing frequency should be determined individually. The duration of warfarin therapy is determined by the type of thrombotic event and the presence or absence of situational triggers (provoked versus unprovoked), thrombophilic states, active cancer, and a history of thrombotic events.