Access II - Trial of Warfarin to Prevent Malfunction of Haemodialysis Catheters

Inclusion Criteria: * Newly placed double-lumen hemodialysis catheter Exclusion Criteria: * Major bleed within last 3 months * Platelet count less than 50 x 10 9/L or current coagulopathy (most recent INR \> 1.5, not due to warfarin) * Active peptic ulcer disease * Anticipated need for invasive intervention within next 2 weeks * Taking warfarin for an indication other than access prophylaxis * Allergic to, or intolerant of, warfarin * Pregnant * Woman of child-bearing age who has not agreed to use an adequate method of birth control for the duration of the study * Catheter likely needed for 2 weeks or less * Patient previously took part in the study * Patient has known aortic aneurysm of 6cm or greater * Patients nephrologist has refused consent * Patient has refused consent