Semilogarithmic plot of plasma acetaminophen levels vs time. Cautions for use of this nomogram: The time coordinates refer to time of ingestion. Serum levels drawn before 4 h may not represent peak levels. The graph should be used only in relation to a single acute ingestion. The lower solid line 25% below the standard nomogram is included to allow for possible errors in acetaminophen plasma assays and estimated time from ingestion of an overdose. Adapted from Rumack BH, Matthew H: Acetaminophen poisoning and toxicity. Pediatrics 55(6): 871–876, 1975; reproduced by permission of Pediatrics .