release preparations, McNeil Consumer Products Co (Fort Washington, Pennsylvania), a manufacturer of acetaminophen, suggests a second APAP level drawn hours after the first; antidotal therapy is to be instituted if either level suggests possible toxicity If the patient has coingested substances that may slow gastric motility (opioids, anticholinergics) and the first level is below the treatment line, draw a second level hours after the first and initiate treatment if the second level is above the treatment line If the patient presents more than to hours after ingestion, initiate NAC therapy, obtain level, and base subsequent course of therapy on nomogram Treatment for patients who present more than 24 hours after ingestion is controversial, as is treatment for patients with subacute, repetitive overdosing over several days or patients with an unknown time of ingestion We consider children who receive more than 150 mg/kg/day for to days to be at risk; but a combination of an undetectable APAP level, normal aminotransferases, and normal INR identifies a patient at low risk of hepatic injury from APAP However, in these settings, either a detectable APAP level or evidence of hepatotoxicity should prompt treatment with a course of NAC If treatment with NAC is indicated, admit the patient to hospital and continue NAC until APAP is undetectable in the blood, until transaminases are improving, and until hepatic function (typically assessed via INR) is normalizing Monitor daily transaminases, INR, renal function, and APAP level to guide decision to continue NAC