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Acetaminophen poison

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In one line

·When you swallow too much acetaminophen, a poison called NAPQI piles up faster than your liver's shield (glutathione) can grab it. NAPQI sticks to liver cells and kills them.

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Normal physiology

·The liver breaks down acetaminophen using three paths. Two safe paths handle most of the dose: one adds a sugar molecule (glucuronidation), another adds a sulfate group (sulfation). Both turn acetaminophen into harmless waste that leaves in your urine. A tiny third path uses an enzyme system called cytochrome P450 (a chemical machine in liver cells) that makes NAPQI, a toxic molecule. Glutathione, a protective chemical your liver makes, immediately grabs every NAPQI molecule and turns it into harmless waste. This system works perfectly at safe doses because glutathione is always ready and waiting.

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What goes wrong

·One upstream break—too much acetaminophen overwhelming the safe paths—explains every downstream finding.

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Hallmark signs

·Nausea and vomiting (Stage 1, first 24 hours)
·Feeling better or no symptoms at all (Stage 2, 24 to 72 hours)
·Pain and tenderness in the right upper belly (Stage 2 to 3)
·Yellow skin and whites of the eyes (jaundice, Stage 3, 72 to 96 hours)
·Confusion, extreme sleepiness, or not responding (encephalopathy, Stage 3)
·Easy bruising, bleeding gums, or bleeding from the stomach or gut (Stage 3)
·Little or no urine output (oliguria, Stage 3)
·Fast heartbeat and low blood pressure (Stage 3 to 4)

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Red flags · escalate now

·INR greater than 1.5 or liver enzymes (ALT or AST) climbing into the thousands—signals severe liver cell death and loss of clotting proteins
·Confusion, sleepiness, or flapping hand tremor when arms are held out (asterixis)—signs ammonia is poisoning the brain
·Blood lactate greater than 3.5 after giving fluids, or blood pH less than 7.30—means massive cell death and very high risk of dying
·Kidney function worsening (rising creatinine) or urine output dropping below 0.5 mL per kilogram per hour—acute kidney injury on top of liver failure
·Reported swallowing more than 10 grams total (or 150 mg per kg of body weight), or blood acetaminophen level plotting above the treatment line on the Rumack-Matthew nomogram—high risk for liver damage if the antidote NAC is not given quickly

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Workup

·Serum acetaminophen level
·Liver enzymes (AST and ALT)
·PT/INR (prothrombin time and international normalized ratio)
·Total and direct bilirubin
·Serum creatinine and BUN (blood urea nitrogen)
·Venous or arterial blood gas with lactate
·Blood glucose
·Basic metabolic panel (sodium, potassium, chloride, bicarbonate)

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Treatment

·NAC (N-acetylcysteine)—the antidote. Oral dosing: 140 milligrams per kilogram loading dose, then 70 milligrams per kilogram every 4 hours for 17 more doses (total 72 hours). IV dosing (preferred in the U.S.): 150 milligrams per kilogram over 1 hour, then 50 milligrams per kilogram over 4 hours, then 100 milligrams per kilogram over 16 hours (total 21 hours; continue longer if liver is still failing).
·Get a detailed history immediately—What drug did you take? Brand name and any combination ingredients? Exact time swallowed (or best estimate)? Total number of pills or total milligrams? Was it one big dose all at once, or spread over hours (staggered dosing)? Why did you take it—accidental, pain relief, or intentional self-harm? Any alcohol or other drugs taken at the same time?
·Monitor liver function tests (ALT, AST, bilirubin, PT/INR) and creatinine every 12 to 24 hours once NAC is started. If the patient is in stage 2 or 3, check every 6 to 12 hours. Continue NAC until ALT is falling, INR is below 2.0, and the patient is clearly improving.
·Contact a liver transplant center early—ideally within 24 hours of hospital arrival—if any King's College Criteria are met: arterial pH below 7.30 after fluids, OR INR above 6.5, OR all three of (1) INR above 3.0, (2) creatinine above 3.4 milligrams per deciliter, and (3) grade 3 or 4 hepatic encephalopathy (deep confusion or coma).
·Activated charcoal by mouth—1 gram per kilogram of body weight (maximum 50 grams in adults), given only if less than 1 to 2 hours since swallowing and the person can protect their airway and will not choke
·IV fluids (normal saline or lactated Ringer's) to maintain blood pressure and kidney blood flow (perfusion), especially if the patient is vomiting or has low blood pressure
·Supportive care for hepatic encephalopathy (brain fog from liver failure)—keep blood sugar above 70 with IV dextrose, correct low sodium, potassium, and phosphate carefully, give lactulose 15 to 30 milliliters by mouth or rectal enema every 6 to 8 hours to lower ammonia, avoid sedatives that deepen coma, and watch for brain swelling (increased pressure inside the skull).

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NCLEX trap

·Start NAC (the antidote) right away if the story and timing point to acetaminophen poisoning. Four hours or more after the person swallowed the pills, draw a blood level and plot it on the Rumack-Matthew chart. Do not wait for lab results to start NAC — every hour you wait kills more liver cells. Labs confirm what happened, but the chart and the clinical picture tell you when to act.
·In the first 24 hours after swallowing acetaminophen, most patients feel fine or have only mild nausea. The belly exam is normal. Do not trust a normal exam early on. Always ask what was swallowed, how much, and when. The poison is already at work inside even when the patient looks well.
·Acetaminophen poisoning happens from one big dose OR from taking too much every day for several days. Repeated overdoses are harder to spot. Always ask how many pills, over how many days, and why. People who take acetaminophen daily for pain can poison themselves by accident, especially if they use several products that all contain acetaminophen — pain pills, cold medicine, sleep aids.
·Why the person took the pills does not change what the poison does inside the body. Whether it was an accident, an impulse, or a suicide attempt, NAPQI (the toxic molecule made from acetaminophen) damages the liver the same way. Give NAC based on the dose swallowed, the time since then, and the blood level on the chart — not on what the patient says their intention was.
·Acetaminophen is the number one cause of sudden liver failure in the United States. Normal doses are safe because the body handles them through two harmless pathways. But when those pathways fill up, extra acetaminophen turns into NAPQI through CYP2E1 (a liver enzyme that normally handles small amounts of toxins), and the body's supply of glutathione (a protective molecule that grabs onto NAPQI and makes it harmless) runs out. Without NAC, severe acetaminophen poisoning causes the liver to fail fast, the blood to stop clotting, confusion or coma, and death. Many patients need a liver transplant to survive.

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