Liver injury, necrosis, or failure resulting from an overdose of acetaminophen. Because acetaminophen is one of the most commonly used over-the-counter (OTC) pain relievers, this is one of the most common poisonings encountered in emergency departments and hospitals. Acetaminophen is found in many OTC and prescription drugs. If a reliable history of the amount of drug can be obtained, ingestions that exceed 7.5 g in the adult or about 150 mg/kg in children should always be considered potentially toxic. In most cases, however, data about overdoses are not reliable, and plasma levels of acetaminophen concentration are routinely measured and compared with standard nomograms to decide whether a patient will need antidotal therapy with N-acetylcysteine.