Modest doses of nitroglycerin do not interfere with beef lung heparin anticoagulation in patients taking nitrates.

The results of a prior clinical report suggested that nitroglycerin may interfere with the anticoagulant effect of heparin. Therefore, 30 adult patients undergoing cardiac surgery were studied in a controlled, prospective fashion. Thirteen patients on chronic nitrate therapy received an intraoperative nitroglycerin infusion at 1 micrograms/kg/min intravenously. Seventeen patients received no preoperative or intraoperative nitrates (control group). Heparin, 300 units/kg, was administered to all patients in three consecutive doses: 40 units/kg, 80 units/kg, and 180 units/kg. The activated coagulation time and activated partial thromboplastin time were measured prior to heparin, and 5 minutes after each heparin dose. There were no differences in automated activated coagulation times or in activated partial thromboplastin times between the groups at any measurement period. The study is limited in that only patients on chronic nitrates were included in the treatment group and that only a modest dose of nitroglycerin was used. However, it is concluded that a modest dose of intravenous nitroglycerin does not interfere with the anticoagulant effect of boluses of beef lung heparin in patients undergoing cardiac surgery.