N-acetylcysteine for Acetaminophen Poisoning Without Hepatotoxicity: the Effect on the Prothrombin Time

ABSTRACT

PURPOSE: In patients with acetaminophen poisoning, clinical severities are partly based on the prothrombin time. In several conditions, N-acetylcysteine (NAC) infusion has been shown to lower the prothrombin index. Thus, we studied the effect of NAC on the prothrombin time in patients intoxicated with acetaminophen without hepatotoxicity. METHODS: From March 2000 to Aug 2004, we reviewed the medical records of 149 patients with a diagnosis of acetaminophen poisoning. After 88 patients had been excluded (29 had hepatocellular injury, 14 had a probable risk based on their normogram, and 45 had a missing prothrombin index value), 61 patients were included in the analysis. The prothrombin time was recorded before and serially during NAC treatment. RESULTS: The mean baseline prothrombin time was 99.1%, 99.3% after intravenous NAC infusion, and 74.0% at 8 hrs after initiation of NAC infusion. It decreased rapidly at 16 hrs, and reached a steady baseline state between 16 to 24 hrs. A rapid increase in the baseline time occurred after 2-3 days when the NAC infusion was stopped. After oral NAC treatment, it decreased rapidly from 8 to 16 hrs, and reached a steady baseline after 2 days. There was a rapid increase after 3~4 days when the NAC infusion was stopped. CONCLUSION: In patients with uncomplicated acetaminophen poisoning, the decrease in the prothrombin index might be misinterpreted as a sign of liver failure, leading to a prolonged treatment.