EFFECT OF INTRAVENOUS NITROGLYCERIN ON HEPARIN DOSAGE REQUIREMENTS INCORONARY-ARTERY DISEASE

Patients admitted to the coronary care unit who received both intraven ous nitroglycerin and heparin were studied to evaluate hepatin dosage requirements. Physicians ordered all nitroglycerin and heparin doses a s well as coagulation studies without knowledge of this study. Activat ed partial thromboplastin time (APTT) values obtained during steady-st ate heparin administration sidered therapeutic if the ratio of APTT/AP TT-baseline was greater-than-or-equal-to 1.5. Sixty patients with myoc ardial infarction or unstable angina were included in the study. The i nitial therapeutic heparin dose of 1,014 +/- 151 units/hour produced a n APTT ratio of 2.0 +/- 0.S. At the time of the initial therapeutic do se, the nitroglycerin dose was 110 +/- 1.08 mug/min. There was a signi ficant correlation between the initial therapeutic dose and both total (r = 0.56; p = 0.0001) and lean (r = 0.26; p < 0.05) body weight. Com parison of patients with nitroglycerin doses < and greater-than-or-equ al-to 100 mug/min revealed a significant difference in the initial the rapeutic dose (971 +/- 147 vs 1,077 +/- 136 U/hour, p < 0.01), but not the initial therapeutic dose standardized to total body weight (14.0 +/- 2.5 vs 13.5 +/- 2.7 U/kg/hour). Similarly, analysis of variance re vealed a significant difference in the initial therapeutic dose (p < 0 .05), but not the initial therapeutic dose standardized to weight amon g 5 different nitroglycerin dosage ranges (10 to 533 mug/min). Neither aspirin use, thrombolytic therapy nor decreasing or discontinuing the nitroglycerin dose significantly affected heparin requirements. Thus, contrary to prior reports, clinically significant heparin resistance induced by nitroglycerin was not found.