Effects of continuous infusion of intravenous nitroglycerin on methemoglobin levels.

The effect of continuous infusion of intravenous nitroglycerin (NTG) on methemoglobin levels in 24 coronary care unit patients was studied. Fifteen patients were admitted with acute myocardial infarction, 5 patients with angina pectoris, 1 patient with congestive heart failure, 2 with chest pain of unknown origin and 1 with chest pain of musculoskeletal origin. Intravenous NTG therapy was initiated at a 5 micrograms/min dose and titrated at 5-micrograms increases until relief of symptoms or until the maximal dose tolerated by each patient. Successive methemoglobin levels were measured at baseline, at each 20 micrograms/min dose increase, at the maximal dose and immediately before weaning the patient from the maximal dose. Statistical analysis by the Student t test (paired samples, p less than 0.05) showed no significant difference between the mean methemoglobin levels at baseline and the mean methemoglobin levels drawn at 20, 40 and 60 micrograms, and before weaning from the maximal dose. No serious adverse effects associated with methemoglobinemia were encountered. It is concluded that intravenous NTG administration in a dose of 0.2 to 2.12 micrograms/min/kg body weight produces no significant methemoglobinemia.