Association of methemoglobinemia and intravenous nitroglycerin administration

Significant elevation of arterial methemoglobin levels has been reported with the administration of intravenous (i.v.) nitroglycerin (NTG). To determine the incidence and clinical significance of this side effect of i.v. NTG, serial arterial methemoglobin levels were determined in 50 consecutive patients receiving i.v. NTG for 48 hours or longer. The mean i.v. NTG infusion rate was 290 ± 13 gmg/min (4.1 ± 0.2 μg/kg/min) and the mean duration of infusion was 7.1 ± 0.5 days. The mean methemoglobin level for the 141 samples was 1.57 ± 0.08%, which differs from the control mean value in our laboratory of 0.44 ± 0.01%. Although no patient had clinical symptoms from methemoglobin, 20 patients had elevated (>1%) levels on at least 1 measurement. Seventy-eight of the 141 samples analyzed were in the normal range; 63 determinations were between 2 and 5%. Patients with normal methemoglobin levels differed from those with abnormal levels in the dose of i.v. NTG (mean infusion rate 244 ± 16 vs 351 ± 17 μg/min; total cumulative dose 1,612 ± 153 vs 3,398 ± 308 mg). Age, weight, renal and hepatic function, and arterial oxygen saturation were not different between the groups. In conclusion, clinically significant methemoglobinemia is uncommon with i.v. NTG infusion; however, when large doses of NTG are administered, this complication is more likely.