Warfarin Sodium for Anticoagulation of Atherosclerotic Miniature Swine

Warfarin sodium (Coumadin) has been used as an effective anticoagulating agent in human medicine for many years, although careful monitoring of its effects are necessary to avoid excessive anticoagulation. Previous experience with this drug for chronic anticoagulation therapy in miniature swine has been limited. The effect of warfarin sodium was studied by measuring prothrombin time in twelve 8-month-old Hanford miniature swine. The pigs had been fed a high-cholesterol diet and had undergone a prior coronary artery abrasion procedure for development of an atherosclerotic coronary disease model. Atherosclerosis was induced by feeding a high-cholesterol diet. Baseline prothrombin time ranged from 12.8 to 15.0 s (13.7 s mean). Prothrombin time was determined daily for the first 5 days of treatment and at least twice weekly thereafter until the animals were sacrificed. Animals received warfarin for 37-41 days. Prothrombin time could be increased 33-50% by once daily oral administration of warfarin 0.04-0.08 mg/kg. Oral administration of more than 0.08 mg/kg as a maintenance dose resulted in the death of two pigs. Most animals responded well to 0.08 mg/kg for the first 3 days of treatment followed by a maintenance dose of 0.06 mg/kg. Dosage was adjusted periodically when prothrombin times exceeded 50% above baseline. It is our experience that monitoring prothrombin time at least twice weekly and adjusting the maintenance dose can eliminate death losses due to warfarin intoxication.