A patient arrives at the emergency department complaining of back pain. He reports taking at least 3 acetaminophen tablets every three hours for the past week without relief. Which of the following symptoms suggests acetaminophen toxicity?
A. Tinnitus
B. Diarrhea
C. Hypertension
D. Hepatic damage
Correct Answer: D. Hepatic damage
Acetaminophen in even moderately large doses can cause serious liver damage that may result in death. Immediate evaluation of liver function is indicated with consideration of N-acetylcysteine administration as an antidote. Acetaminophen is rapidly absorbed from the gastrointestinal (GI) tract and reaches therapeutic levels in 30 minutes to 2 hours. Overdose levels peak at 4 hours unless other factors could delay gastric emptying, such as a co-ingestion of an agent that slows gastric motility, or if the acetaminophen is in an extended-release form.
Option A: Tinnitus is associated with aspirin overdose, not acetaminophen. Acetaminophen has an elimination half-life of 2 hours, but can be as long as 17 hours in patients with hepatic dysfunction. It is metabolized by the liver, where it is conjugated to nontoxic, water-soluble metabolites that are excreted in the urine.
Option B: In the third stage (72 hours to 96 hours), liver dysfunction is significant with renal failure, coagulopathies, metabolic acidosis, and encephalopathy. Gastrointestinal (GI) symptoms reappear, and death is most common at this stage. The fourth stage (4 days to 3 weeks) is marked by recovery.
Option C: Diarrhea and hypertension are not associated with acetaminophen. The diagnosis of acetaminophen toxicity is based on serum levels of the drug, even if there are no symptoms. Other laboratory studies needed include liver function tests (LFTs) and coagulation profile (PT/INR). If the ingestion is severe, LFTs can rise within 8 to 12 hours of ingestion. Normally LFTS remain elevated in the second stage at 18 to 72 hours.