Toxic acetaminophen dosages. In adults, an acute ingestion of more than 150 mg/kg or 12 g of acetaminophen is considered a toxic dose and poses a high risk of liver damage. In children, acute ingestion of 250 mg/kg or more poses significant risk for acetaminophen-induced hepatotoxicity.istorically, the maximum daily adult dose of acetaminophen is 4 g, with a recommended dosage of 352-650 mg every 4-6 hours or 1 g every 6 hours.