N-Acetylcysteine Reduces Methemoglobin in Vitro, , ,

Study objective: To determine whether N-acetylcysteine (NAC)reduces methemoglobin. Methods: We carried out an in vitro laboratory experiment in which five healthy adult volunteers donated blood. Each sample was divided equally among three test tubes. Tube 1 served as a negative control. Sodium nitrite .18 mol/L with dextrose .28 mol/L was added to tube 2 and to tube 3. Next, phosphate-buffered saline solution (PBS) was added to tube 2 and NAC (200 mg/mL) to tube 3. Serial methemoglobin levels were measured over 5.5 hours. Results: Maximum methemoglobin levels were observed at 1.5 hours for both the NAC-nitrite and the PBS-nitrite sample (62.7%±8.1% and 65.1%±7.0%, respectively; data expressed as mean±SD). The mean difference in methemoglobin between NAC-nitrite and PBS-nitrite was significant at 4.5 hours (29.3%±23.0%, P=.046). The mean rate of methemoglobin decline in NAC-nitrite samples was also different from that of PBS-nitrite samples (10.7%±1.0% versus 2.9%±2.3%, P=.002). The rate of decline was linear (zero order) in the NAC-nitrite samples and represented by the equation: % change methemoglobin =.18 × time in minutes. Area under the concentration-time curve was also different among groups (P<.05). Conclusion: In this in vitro model, NAC reduced chemically induced methemoglobin. [Wright RO, Magnani B, Shannon MW, Woolf AD: N-acetylcysteine reduces methemoglobin in vitro. Ann Emerg Med November 1996;28:499-503.]