Staggered Acetaminophen Ingestion With Early Coagulopathy
A 39-year-old man with alcohol use disorder is brought in 14 hours after the first of several handfuls of 500-mg acetaminophen tablets, taken over 6 hours after a weekend binge. He vomited twice and has right upper quadrant tenderness. HR 112, BP 102/64, temperature 37.1 C. Acetaminophen is 38 micrograms/mL by immunoassay, ethanol 120 mg/dL, ALT 180 U/L, AST 210 U/L, INR 1.4, bicarbonate 19 mmol/L, creatinine 1.0 mg/dL. He is alert and tremulous. No other ingestions are reported, and the exact number of tablets is unknown. The local poison center is busy.
1. Should the Rumack-Matthew nomogram be used to decide treatment? Explain, including how the timing and the ethanol result affect your interpretation.
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No. The Rumack-Matthew nomogram is validated only for a single, acute, well-timed ingestion with a level drawn at least 4 hours after that ingestion. Here the ingestion was staggered over 6 hours, the first and last doses are uncertain, and the patient already has coagulopathy and transaminitis. A level of 38 micrograms/mL at 14 hours may reflect the last dose rather than the peak, so plotting it would falsely reassure. Ethanol also complicates interpretation: acute ethanol can transiently inhibit CYP2E1, but it does not exclude injury once ethanol is metabolized, and this patient has clinical and laboratory evidence of hepatotoxicity. Action: start acetylcysteine immediately and do not wait for a repeat level or for the nomogram to clarify.
2. Write your acetylcysteine orders and the criteria you will use to decide how long to continue it.
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Acetylcysteine: 150 mg/kg IV over 1 hour, then 50 mg/kg over 4 hours, then 100 mg/kg over 16 hours. Because this is a staggered ingestion with established injury, do not stop automatically at 21 hours. Check ALT/AST, INR, creatinine, glucose, pH, lactate, and mental status every 6-12 hours. Continue NAC until transaminases are improving and INR is falling toward normal; if INR rises, encephalopathy develops, or acidosis persists, continue and involve transplant. Repeat the acetaminophen level if there is concern about ongoing absorption. Watch for anaphylactoid reaction and slow the infusion if it occurs; the risk of undertreating is greater.
3. Which findings would trigger transfer to a transplant center, and what is the role of fomepizole or cimetidine in this scenario?
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Transfer criteria: King's College criteria - pH below 7.3 after resuscitation, INR above 6.5, creatinine above 3.4 mg/dL, or grade III-IV encephalopathy; an early lactate above 3.5 mmol/L also warrants urgent discussion. Rising INR, hypoglycemia, or worsening acidosis should prompt early transfer even if criteria are not yet fully met. Fomepizole is not indicated for acetaminophen; it is a CYP2E1 inhibitor but is not used for this poisoning. Cimetidine is also not routine. The priority is NAC and supportive care, not additional antidotes.