During the first stage, which lasts from 12 to 24 hours, there may be anorexia, nausea, vomiting, diaphoresis and pallor. After 24 hours, earlier symptoms tend to abate and the patient may even feel well for one or a few days. Unfortunately, during this second phase, hepatic enzymes, serum bilirubin and prothrombin time begin to rise as hepatic necrosis progresses and tenderness may develop in the right upper quadrant. Three to 5 days after drug ingestion, the third phase sets in for those patients who develop significant hepatic necrosis. This phase is marked by the sequelae of hepatic necrosis which include jaundice, coagulation effects, hypoglycemia, encephalopathy as well as renal failure and myocardiopathy.
Death occurs as a result of hepatic failure.
There is some evidence to suggest that NAC may offer some protection even when given up to 24 hours after drug ingestion. The hepatotoxicity of acetaminophen is related to a secondary, reactive metabolite which is detoxified by conjugation with hepatic glutathione. A large overdosage of acetaminophen will result in an increased formation of the reactive metabolite which in turn may deplete stores of glutathione in the liver. Antidotes such as NAC probably act by restoring glutathione levels. The stomach should be emptied promptly.