- Patients who are taking warfarin for maintenance of central venous catheter patency are eligible for this trial if their INR < 1.2. Because of the interaction between warfarin and Oxandrin, the maintenance dose of warfarin in eligible patients should be halved to keep the INR at 1-1.2. For example, if a patient is taking 1 mg of warfarin at study entry, it is recommended that the dose be decreased to 0.5 mg per day, their dose should be decreased to every other day, every third day, etc. to keep the INR at < 1.2. The INR must be checked weekly until stable at < 1.2.