A Basis for the Decision to Rule in or out Acetaminophen Toxicity: Assessment of the Serum Level Within 4 Hours Post Overdose

Background: Acetaminophen is a popular antipyretic and analgesic medication worldwide; however, its therapeutic window is narrow, which may lead to overdose or toxicity. This study was conducted to assess the correlation between the serum acetaminophen levels before and 4 hours after the acute toxicity with this drug. The objective of this study was to test the validity of the serum level to arrive at a clinical decision on the toxicity with acetaminophen. Methods: This cross-sectional study was performed on patients hospitalized and treated with a diagnosis of acute acetaminophen overdose during one year (Sept. 2018 to Sept. 2019) at the Toxicology Department of Imam Reza Hospital, Mashhad, Iran. Patients were analyzed for demographics, time of ingestion, their first and second serum acetaminophen concentrations. Results: A total of 204 patients (106 male & 98 female) were included in this study. The average dose of acetaminophen ingestion by these patients was 14.5±3.50 g and all patients were treated successfully with N-Acetyl-Cysteine (NAC). The variables of age (P=0.293), serum acetaminophen levels at 1-2 h (P=0.679), and at 2-3 h (P=0.126) did not have significant relationships with the serum acetaminophen level on the fourth hour. However, the serum acetaminophen levels tested between 3-4 h and acetaminophen intoxication dosage had significant relationships with the acetaminophen level on the fourth hour. Conclusion: In patients with acute acetaminophen toxicity, the data on the serum levels obtained before a 4-hour timepoint from the ingestion were not useful to decide on the need for the rescue treatment with N-acetyl-cysteine.