ABSTRACT
Warfarin is a particularly effective drug in the prevention of deep vein thrombosis (DVT), pulmonary embolism, embolisation in atrial fibrillation and some prosthetic heart valves. It is also used during haemodialysis and to prevent myocardial infarction in patients with unstable angina. Its initial use was as rat poison. If you think of this every time you prescribe warfarin or co-prescribe it with another drug, you may avoid its becoming a human poison! As all family doctors and warfarin clinic nurses know, there is only a small difference between the clinically effective dose and the toxic dose, for a given patient. The interacting drug potentiates warfarin – e.g. the anti-coagulation effect of warfarin is added to that of an NSAID (which may have been bought in a supermarket or convenience store). If the NSAID has caused a peptic ulcer, any gastrointestinal bleed ing is likely to be severe and difficult to stop, because of the degree of anticoagulation by warfarin.
