A CLINICAL AND IN-VITRO STUDY ON THE POSSIBLE INTERACTION OF INTRAVENOUS NITRATES WITH HEPARIN ANTICOAGULATION

It has been reported that intravenous nitrates inhibit the anticoagula nt effect of heparin. This possible interaction has potentially seriou s implications for the management of patients with acute coronary isch emic syndromes. This possible interaction was assessed prospectively i n a clinical and in an in vitro study involving 24 patients receiving both drugs for the management of unstable angina pectoris. There was a small inhibitory effect of intravenous glyceryl trinitrate or isosorb ide dinitrate on the anticoagulant effect of heparin in 3 of 24 cases in vivo, as assessed by activated partial thromboplastin time measurem ents. Nitrates or propylene glycol had no effect on heparin activity i n vitro. It was concluded that there may be an inhibitory effect of ni trates on anticoagulation in a small minority of patients, but close a ttention to detail in monitoring heparin anticoagulation is far more i mportant.