Emergency & Toxicology

Acetaminophen toxicity: Rumack-Matthew and N-acetylcysteine

Clinical Overview and When to Suspect Acetaminophen Toxicity

— ≥150 mg/kg (or ≥7.5 g in adults) = potentially toxic

— ≥200 mg/kg in children <6 yr more conservative

— Any intentional overdose or polypharmacy ingestion (co-ingestants common: opioids, SSRIs, ETOH)

— Unexplained AST/ALT in the thousands with normal alk phos and modest bilirubin

— AST > ALT with massive transaminitis ("classic APAP pattern")

— Altered mental status + coagulopathy in a young patient → think ALF

— Chronic ingestion in a malnourished, alcoholic, or fasting patient taking "therapeutic" doses (4 g/day can injure if CYP2E1 induced and glutathione depleted)

— Stage I (0–24 h): asymptomatic or N/V, malaise — labs may be normal

— Stage II (24–72 h): RUQ pain, rising AST/ALT, INR, bilirubin; renal function may worsen

— Stage III (72–96 h): peak hepatotoxicity, encephalopathy, lactic acidosis, hypoglycemia, AKI

— Stage IV (4 d–2 wk): recovery vs. progression to ALF/death

Board pearl: A patient who appears "well" 12 hours after a large APAP ingestion is the classic trap — they are in Stage I. Do not be reassured by a normal exam or normal LFTs early. Get a 4-hour (or later) level and plot on the Rumack–Matthew nomogram.

Acetaminophen (APAP) is the #1 cause of acute liver failure (ALF) in the US, responsible for ~50% of cases and the majority of ALF-related transplants.

Toxicity arises when glutathione stores are depleted, allowing the reactive metabolite NAPQI (formed via CYP2E1) to bind hepatocyte proteins → centrilobular (zone 3) necrosis.

Single acute ingestion thresholds:

When to suspect even without a clear history:

Clinical course (acute single ingestion):

Mortality without N-acetylcysteine (NAC) in severe cases is high; with timely NAC (<8 h), hepatotoxicity is rare.

Presentation Patterns and Key History

— Acute single ingestion with known time → use Rumack–Matthew nomogram

— Staggered/repeated supratherapeutic ingestion (e.g., taking extra Tylenol/Percocet for pain over days) → nomogram does NOT apply

— Unknown time of ingestion or delayed presentation >24 h → nomogram does not apply

— Exact time of ingestion (or time of first dose if staggered)

— Total dose and formulation (immediate-release vs. extended-release; combination products like Percocet, Vicodin, NyQuil, Excedrin)

— Co-ingestants — anticholinergics or opioids may delay gastric emptying and prolong absorption

— Suicidal intent vs. accidental (pediatric exploratory vs. therapeutic misadventure)

— Risk factors for enhanced toxicity: chronic alcohol use, malnutrition/fasting, isoniazid, phenytoin, carbamazepine, rifampin, St. John's wort (CYP2E1/3A4 inducers)

— Vomiting in first 4–12 h does not predict severity

— RUQ pain at 24–48 h suggests hepatocellular injury already underway

— Confusion, asterixis, jaundice, bleeding → Stage III, late and ominous

— Most childhood ingestions are accidental and small; many do not reach toxic thresholds

— Always weigh-base dose calculations

— Children <6 may actually have better outcomes than adults at equivalent mg/kg due to higher sulfation capacity

Key distinction: Single acute vs. repeated supratherapeutic ingestion fundamentally changes your decision pathway. For repeated/staggered ingestions, treat based on AST/ALT and APAP level >10 mcg/mL rather than the nomogram. Missing this distinction is the most common Step 3 wrong-answer trap.

Three classic presentations to recognize on Step 3:

Key history elements to elicit:

Symptom timeline mapping:

Pediatric considerations:

Physical Exam Findings and Hemodynamic Assessment

— Mild nausea, vomiting, diaphoresis, pallor

— Vitals usually normal — do not let this falsely reassure

— RUQ tenderness with hepatomegaly

— Mild tachycardia, possible orthostasis from volume losses

— Subtle rise in INR before clinical bleeding

— Jaundice, scleral icterus

— Hepatic encephalopathy: asterixis, confusion, somnolence → coma (grade I–IV by West Haven)

— Coagulopathy: ecchymoses, GI bleeding, oozing IV sites

— Hypoglycemia (failed gluconeogenesis) — check fingersticks q1–2 h

— Lactic acidosis with Kussmaul respirations

— AKI (~25%) — direct tubular injury from NAPQI, often out of proportion to hepatic failure

— Hemodynamic: distributive shock-like state — warm, vasodilated, low SVR, high CO

— Worsening encephalopathy, Cushing reflex (HTN + bradycardia), pupillary changes

— Rising lactate despite resuscitation

— pH <7.30 after fluid resuscitation = King's College criterion

Step 3 management: A patient at 72 hours with jaundice + INR 4 + asterixis + creatinine 2.5 needs simultaneous moves: continue IV NAC, place on transplant center radar, transfer to ICU at a liver transplant facility, monitor q1h neuro checks, glucose q1–2h, head-of-bed 30°, avoid sedation that obscures mental status, and call hepatology/transplant early — don't wait for King's College criteria to be met.

Stage I (0–24 h): exam is often deceptively normal

Stage II (24–72 h):

Stage III (72–96 h) — fulminant pattern:

Stage IV (recovery): resolving jaundice, normalizing INR — or progression

Hemodynamic red flags suggesting ALF/cerebral edema:

Diagnostic Workup — Initial Labs and the 4-Hour APAP Level

— Serum acetaminophen level — timing is critical

— AST, ALT, total bilirubin, INR/PT, albumin

— BMP (creatinine, bicarbonate, glucose)

— Lactate, ABG/VBG

— Lipase (pancreatitis can occur)

— Salicylate level (common co-ingestion)

— Urine pregnancy in any reproductive-age female

— EtOH, urine drug screen for co-ingestants

— ECG if any TCA, opioid, or unknown co-ingestion

— Draw the APAP level no earlier than 4 hours post-ingestion (absorption complete; nomogram only valid from 4–24 h)

— If patient presents at 2 h: give activated charcoal if <2 h since ingestion and airway protected, then draw level at 4 h

— If presenting >4 h: draw immediately

— Y-axis: serum APAP (mcg/mL, log scale)

— X-axis: hours since ingestion

— Treatment line starts at 150 mcg/mL at 4 h, declining to ~37 mcg/mL at 12 h, ~4.7 mcg/mL at 24 h

— Above the line → treat with NAC

— The original "probable toxicity" line at 200 mcg/mL is not used in the US; the 150 line is standard

— AST/ALT >1000 with AST often > ALT

— INR elevation — sensitive marker of synthetic dysfunction

— Normal alk phos (helps distinguish from cholestatic causes)

Board pearl: APAP level drawn before 4 hours is uninterpretable on the nomogram (still absorbing). The exception: a level that is already markedly elevated before 4 h with a clearly toxic dose history — start NAC empirically and recheck.

Send immediately on any suspected ingestion:

The 4-hour rule:

Plot on the Rumack–Matthew nomogram:

Lab patterns supporting toxicity:

Diagnostic Workup — Advanced and Confirmatory Studies

— Unknown time of ingestion

— Staggered/repeated supratherapeutic dosing

— Extended-release formulations (consider repeat level at 4 and 8 h)

— Co-ingestion of agents delaying gastric emptying (opioids, anticholinergics)

— Presentation >24 hours post-ingestion

— APAP level >10 mcg/mL at any time, OR

— AST or ALT elevated above normal, OR

— Reported toxic ingestion with unreliable level/timing

— APAP level, AST/ALT, INR, creatinine, bicarbonate q4–6 h initially, then q12 h once trending down

— Glucose q1–2 h if encephalopathic

— King's College Criteria for ALF transplant listing:

— Arterial pH <7.30 after resuscitation, OR

— All three: INR >6.5 (PT >100 s) + creatinine >3.4 mg/dL + grade III/IV encephalopathy

— Lactate >3.5 early or >3.0 after resuscitation

— Phosphate >3.7 mg/dL at 48–96 h (failure of hepatic regeneration)

— Not routinely needed for diagnosis

— RUQ US if cholestatic pattern, considering alternative diagnosis

— Non-contrast head CT if encephalopathy worsens — rule out cerebral edema/hemorrhage

CCS pearl: On CCS, after starting NAC, advance the clock in short intervals (2–4 h) and re-order LFTs, INR, APAP level, BMP at 8–12 h. Forgetting to re-check the APAP level and INR before stopping NAC is a frequent points-loser — NAC continuation depends on these trends, not a fixed duration.

When the nomogram does NOT apply — common Step 3 scenarios:

In these cases, treat empirically with NAC if:

Serial monitoring during NAC:

Markers of severe injury / poor prognosis:

Imaging:

EEG if subclinical seizures suspected in late-stage hepatic encephalopathy

Risk Stratification and Treatment Decision Logic

— Step 1: Time of ingestion known and single acute?

— Yes → draw 4-h level → plot on Rumack–Matthew → above line = NAC

— No → go to Step 2

— Step 2: Unknown time, staggered, or late presentation?

— Check APAP level + AST/ALT

— AST/ALT elevated OR APAP >10 mcg/mL → start NAC

— Step 3: History of toxic dose (≥150 mg/kg or ≥7.5 g) with pending labs?

— Start NAC empirically if labs delayed >8 h from ingestion; stop if level falls below line and LFTs normal

— NAC is maximally effective if started within 8 hours of ingestion

— After 8 h, efficacy decreases but NAC still benefits patients out to 24+ hours, and is given even in established hepatotoxicity (improves microcirculation, antioxidant effect)

— Never withhold NAC waiting for a level if >8 h have passed since a toxic dose

— Useful if presenting <2 hours post-ingestion (some extend to 4 h for large doses)

— Adsorbs APAP effectively; does not interfere with PO NAC significantly

— Contraindicated: altered mental status without airway protection, ileus, caustic co-ingestion

— Chronic ETOH, malnutrition, INH, antiepileptics, prolonged fasting

— Some experts use a "100 line" (more conservative) in these high-risk patients, though guideline support varies

Step 3 management: When in doubt, give NAC. It is exceedingly safe, and the cost of missing toxicity (ALF, death, transplant) vastly exceeds the cost of unnecessary treatment.

Algorithmic approach — commit this to memory:

The "8-hour rule":

Activated charcoal:

Risk modifiers lowering threshold to treat:

Pharmacotherapy — N-Acetylcysteine Regimens

— Replenishes glutathione to detoxify NAPQI

— Acts as a glutathione substitute directly

— Improves hepatic microcirculation and oxygen delivery; antioxidant in established injury

— Loading: 150 mg/kg IV over 60 minutes (use 60 min, not 15, to reduce anaphylactoid reactions)

— Dose 2: 50 mg/kg IV over 4 hours

— Dose 3: 100 mg/kg IV over 16 hours

— Total: 300 mg/kg over 21 h

— 140 mg/kg loading, then 70 mg/kg q4h × 17 doses

— Smells/tastes like rotten eggs — dilute in juice/cola; antiemetics often needed

— Avoid if vomiting, GI bleeding, ileus, or altered mentation

— IV preferred in: fulminant hepatic failure, pregnancy, intractable vomiting, GI bleed, altered mental status

— Either route equally effective if completed

— All of: APAP undetectable, AST/ALT normal or clearly declining, INR <2.0, patient clinically well

— If criteria not met → continue NAC at 6.25 mg/kg/h (extension of dose 3 rate) until met

— Anaphylactoid reaction in 10–20% of IV recipients (histamine release, NOT IgE) — flushing, urticaria, bronchospasm

— Management: pause infusion, give diphenhydramine ± albuterol; resume at slower rate once resolved

— Hyponatremia from dilution in pediatrics — use weight-based dilution volumes

— Rarely: true anaphylaxis (asthmatics at higher risk)

Board pearl: Anaphylactoid reactions to IV NAC are not a contraindication to continuing therapy — slow the rate and pretreat. Stopping NAC for a rash and losing hepatoprotection is the wrong answer.

Mechanism of NAC:

IV NAC — 21-hour protocol (Prescott regimen, US standard):

PO NAC — 72-hour protocol:

Choice of route:

Duration — when to STOP NAC (after completing 21 h):

Adverse effects:

Advanced Management and Adjunctive Therapies

— Glucose: D10 or D5 infusion; check fingersticks q1–2 h — hypoglycemia is a major killer

— Coagulopathy: do NOT routinely correct INR with FFP unless bleeding or invasive procedure planned — INR is a key prognostic marker; correcting it blinds you

— Vitamin K 10 mg IV — reasonable if INR elevated, low cost

— Electrolytes: correct hypophosphatemia, hypokalemia, hypomagnesemia aggressively

— Lactic acidosis: treat underlying perfusion; bicarbonate only for severe pH <7.1

— Lactulose has limited role in acute ALF (unlike cirrhosis) — may worsen ileus and cerebral edema

— Focus on cerebral edema prevention: head of bed 30°, normothermia, normocapnia, avoid hypotonic fluids

— Hypertonic saline (target Na 145–155) or mannitol for elevated ICP

— Intubate for grade III/IV encephalopathy; consider ICP monitoring at transplant centers

— AKI in ~25% — supportive; CRRT preferred over intermittent HD (hemodynamic stability, ammonia clearance)

— Hemodialysis removes APAP — consider if massive ingestion (APAP >900 mcg/mL at 4 h), severe acidosis, coma, or hemodynamic instability

— Increase NAC dose during HD (it's also dialyzed)

— Listing based on King's College criteria

— MELD less useful in acute setting

— Survival without transplant once criteria met: <20%

— Early transfer to a transplant center is the single highest-yield decision

CCS pearl: Order "transfer to liver transplant center" as soon as you see INR >2.0 at 24 h, encephalopathy, acidosis, or rising creatinine. Don't wait for King's criteria to be fully met — transport takes time and worsening patients lose transplant candidacy.

Supportive care of established hepatotoxicity:

Hepatic encephalopathy in APAP-ALF:

Renal support:

Extracorporeal removal of APAP:

Liver transplantation:

Special Populations — Elderly and Renal/Hepatic Impairment

— Higher baseline rates of polypharmacy and combination APAP products (Vicodin, Percocet, OTC cold medicines)

— Unintentional chronic supratherapeutic ingestion is more common than acute overdose

— Lower glutathione reserves and reduced hepatic mass → injury at lower thresholds

— Comorbid CKD/CHF complicates fluid management during NAC infusion

— Threshold to treat should be lower; check APAP level even with modest LFT elevation of unclear etiology

— Surprisingly, cirrhotic patients are NOT at clearly increased risk from therapeutic doses

— However, less hepatic reserve means a smaller acute injury has bigger clinical consequences

— Maximum daily APAP for cirrhotics: 2 g/day (some recommend up to 3 g short-term); avoid in active alcohol use

— NAC dosing unchanged

— CYP2E1 induction → more NAPQI per dose

— Glutathione depletion from malnutrition

— Toxicity can occur at "therapeutic" doses (3–4 g/day in fasting alcoholic)

— Treat aggressively even with moderately elevated levels

— APAP itself can cause AKI independent of liver injury (especially in massive ingestions)

— NAC dosing is not adjusted for renal function

— If on hemodialysis, give NAC during and increase dose (or run continuously)

— Isoniazid, rifampin, phenytoin, carbamazepine, phenobarbital, St. John's wort, chronic ETOH

Key distinction: Chronic alcoholic + therapeutic-dose APAP + fasting is a classic Step 3 stem for toxicity at "non-toxic" doses. AST often >ALT and both in the thousands — pathognomonic for APAP, not viral hepatitis (which rarely exceeds 2000 and has ALT > AST).

Elderly patients:

Pre-existing liver disease (cirrhosis, NASH, hepatitis C):

Chronic alcohol use:

Renal impairment:

Drug interactions enhancing toxicity (CYP2E1/3A4 inducers):

Special Populations — Pregnancy and Pediatrics

— APAP crosses the placenta; fetus develops CYP2E1 by ~14 weeks → fetal hepatotoxicity possible

— Treat the mother aggressively — maternal survival is paramount and improves fetal outcome

— IV NAC is preferred (faster, ensures dose, no GI issues with hyperemesis)

— NAC is Category B / safe in pregnancy

— Do not delay NAC for fetal monitoring; OB consult for ongoing fetal surveillance

— Threshold for treatment is identical — use the same nomogram

— Delivery decisions individualized; ALF in pregnancy carries high maternal/fetal mortality

— Most pediatric ingestions are exploratory and sub-toxic

— Toxic threshold: ≥200 mg/kg in children <6 yr (vs. 150 mg/kg adult)

— Children <6 often have better outcomes at equivalent mg/kg due to greater sulfation

— Liquid pediatric formulations (160 mg/5 mL) — calculate carefully

— Dosing errors in caregivers (using adult product, q4h instead of q6h) is a recognized cause of toxicity

— NAC: same weight-based dosing; dilute in smaller fluid volumes in children <40 kg to avoid hyponatremia and fluid overload

— Intentional overdose with suicidal intent is common

— Mandatory psychiatric evaluation before discharge

— Screen for co-ingestants, sexual assault, and abuse

— APAP is compatible with breastfeeding at therapeutic doses

— NAC is compatible

Step 3 management: A 16-year-old who took 30 extra-strength Tylenol 6 h ago, level pending → start IV NAC empirically while awaiting level, place on suicide precautions, sitter at bedside, remove access to harm, and consult psychiatry. Do not discharge even if levels return non-toxic until psychiatric clearance.

Pregnancy:

Pediatrics:

Adolescents:

Breastfeeding:

Complications and Adverse Outcomes

— APAP is the leading cause of ALF in the US and UK

— Characterized by coagulopathy (INR ≥1.5) + encephalopathy in a patient without pre-existing liver disease

— Mortality 25–30% even with NAC; transplant-free survival highest with APAP etiology (~65–70%) vs. other causes

— Leading cause of death in ALF

— Risk increases with grade III/IV encephalopathy and ammonia >150–200 µmol/L

— Manage: HOB 30°, hypertonic saline (Na 145–155), normothermia (33–36°C), mannitol, intubation, normocapnia (PaCO2 35–40)

— 25–50% of severe cases; direct tubular toxicity from NAPQI

— May require CRRT; usually reversible if patient survives

— Early (within hours): from mitochondrial dysfunction at very high APAP levels — predicts severe toxicity

— Late: from hepatic failure and shock

Board pearl: Lactate >3.5 mmol/L early (within hours of presentation) in massive APAP ingestion is a marker of mitochondrial toxicity and predicts severe outcomes — these are the patients to discuss with a transplant center immediately, even before transaminitis appears.

Acute liver failure (ALF):

Cerebral edema and intracranial hypertension:

Acute kidney injury:

Lactic acidosis:

Pancreatitis: uncommon but reported; check lipase if abdominal pain

Hypoglycemia: failed gluconeogenesis — can be sudden and severe

Multi-organ failure: distributive shock, ARDS, DIC, GI bleeding

Anaphylactoid reaction to NAC: 10–20% of IV recipients; manageable

Death: Without NAC, large ingestions carry mortality 10–30%; with early NAC, mortality <1%

When to Escalate Care — ICU, Consults, Transfer

— Encephalopathy (any grade) or altered mental status

— INR >2.0 at 24 h or rising

— pH <7.35 or lactate >3.0 after resuscitation

— Hypoglycemia requiring continuous dextrose

— AKI with creatinine rising

— Hemodynamic instability

— Massive ingestion with APAP >500 mcg/mL at 4 h or >900 mcg/mL (consider HD)

— Most NAC-treated patients without organ dysfunction

— Serial LFTs/INR/BMP q6–12 h

— APAP level below treatment line at 4 h, asymptomatic, reliable history, no co-ingestants, no psychiatric concerns

— Always psychiatric evaluation before discharge of any intentional ingestion

— Medical toxicology / Poison Control (1-800-222-1222) — call for every APAP overdose; documents care, guides nomogram interpretation, handles atypical cases

— Hepatology for any transaminitis >1000 or coagulopathy

— Psychiatry for intentional ingestions before any disposition

— Liver transplant center when meeting any concerning trajectory

— INR >2.0 at any time post-ingestion

— Encephalopathy of any grade

— Acidosis (pH <7.35) after resuscitation

— Rising creatinine

— Lactate >3.5 early

CCS pearl: Call Poison Control on every case — it's both medically and medicolegally correct. On CCS, the orders to add include: "Consult toxicology," "Consult psychiatry" (for intentional), "Transfer to ICU" if any organ dysfunction, and "Transfer to liver transplant center" for ALF trajectory.

ICU admission criteria:

Floor admission for monitored therapy:

Discharge from ED:

Consults to call early:

Transfer to transplant center triggers (don't wait for King's criteria):

Key Differentials — Other Toxin-Mediated Hepatotoxicity

— Acetaminophen toxicity — the prototype

— Ischemic hepatitis ("shock liver") — hypotension, sepsis, heart failure; LDH also markedly elevated; rapid rise and fall over days

— Amanita phalloides mushroom poisoning — biphasic course with severe GI symptoms followed by hepatotoxicity at 48–72 h; treat with silibinin/penicillin G

— Carbon tetrachloride, halothane, kava — environmental/anesthetic exposures

— Isoniazid — usually ALT > AST, idiosyncratic, weeks to months

— Valproate — micro/macrovesicular steatosis, hyperammonemia

— Statins — typically mild, rarely severe

— Antibiotics: amox-clav (cholestatic, weeks after exposure), nitrofurantoin

— Herbals: kava, comfrey, green tea extract, bodybuilding supplements

— AST > ALT (usually 2:1) but rarely >300

— If LFTs >500, look for another cause (often APAP co-injury)

Key distinction: Transaminitis in the thousands in an alcoholic patient is NOT alcoholic hepatitis — it's almost always APAP toxicity (often "therapeutic" doses) or ischemic hepatitis. The Step 3 trap is calling it "alcoholic hepatitis" and missing treatable APAP injury. Check the APAP level reflexively.

Differential for AST/ALT >1000 with AST > ALT pattern ("toxic/ischemic" pattern):

Other drug-induced liver injury (DILI):

Cocaine, MDMA, ecstasy: hepatotoxicity often combined with hyperthermia/rhabdo

Iron overdose: vomiting + hematemesis + metabolic acidosis + liver injury; deferoxamine for chelation

Alcoholic hepatitis:

Key Differentials — Non-Toxic Causes of Acute Hepatitis

— Hepatitis A: fecal-oral, self-limited, rarely fulminant in adults

— Hepatitis B: acute and chronic; can be fulminant especially with HDV co-infection

— Hepatitis E: waterborne; severe in pregnancy (20% mortality in 3rd trimester)

— HSV, EBV, CMV, VZV in immunocompromised

— ALT typically > AST, both in 1000s but rarely >5000 (APAP routinely >5000)

— Young/middle-aged women, hypergammaglobulinemia, ANA/SMA/anti-LKM positive

— Subacute onset, biopsy with interface hepatitis

— Young patient (<40), low alk phos:bilirubin ratio (<4), hemolytic anemia, ceruloplasmin low, Kayser-Fleischer rings

— Acute fulminant Wilson's: classic presentation in adolescents

— Hepatic vein thrombosis; hypercoagulable state; tender hepatomegaly, ascites

— Doppler US diagnostic

— 3rd trimester; AST/ALT moderately elevated, hypoglycemia, coagulopathy

— Delivery is the treatment

— Recent hypotension, LDH markedly elevated, rapid resolution with hemodynamic support

Board pearl: When ALF is the diagnosis, the ALF workup panel must include: APAP level, viral hepatitis serologies (HAV IgM, HBsAg, anti-HBc IgM, HCV RNA, HEV IgM), ceruloplasmin, ANA/ASMA, pregnancy test, toxicology screen, RUQ Doppler US. Sending only "LFTs" misses the etiology.

Viral hepatitis (acute):

Autoimmune hepatitis:

Wilson's disease:

Budd-Chiari syndrome:

Acute fatty liver of pregnancy / HELLP syndrome:

Ischemic hepatitis:

Disposition, Discharge Planning, and Long-Term Considerations

— Completed NAC course (21 h IV or 72 h PO)

— APAP undetectable, AST/ALT normalizing/normal, INR <2.0, clinically well, tolerating PO

— No co-ingestant complications outstanding

— Formal psychiatric evaluation with disposition (inpatient vs. intensive outpatient vs. outpatient)

— Lethal means restriction counseling for family — remove medications from home

— Safety plan documented

— Outpatient follow-up arranged with psychiatry within 7 days (ideally within 72 h)

— National Suicide Prevention Lifeline (988) information provided

— Maximum APAP dose: 4 g/day in healthy adults; 2–3 g/day in chronic alcohol use, malnutrition, or cirrhosis

— Recognize hidden APAP in combination products: Percocet, Vicodin, NyQuil, Excedrin, Theraflu

— Avoid stacking OTC and prescription APAP-containing products

— Use weight-based dosing in children; do not exceed 75 mg/kg/day

— Hepatology follow-up at 4–6 weeks with repeat LFTs/INR

— Avoid alcohol for at least 6 months; ideally permanently if intentional ingestion

— Avoid further APAP if possible during recovery

Step 3 management: Never discharge an intentional ingestion patient without documented psychiatric clearance — even if medically stable. Discharging a "medically cleared" suicide attempt without psych eval is a board-favorite patient safety / liability wrong answer.

Medically clear for discharge when:

Before discharge after intentional ingestion:

Outpatient counseling for accidental/therapeutic-misadventure ingestion:

No specific hepatology follow-up needed if LFTs normalized and no underlying liver disease — APAP injury, once resolved, does not cause chronic liver disease

If survived with residual injury:

Follow-Up, Monitoring, and Patient Counseling

— APAP, AST, ALT, INR, BUN/Cr, glucose, lactate, bicarbonate q6–12 h

— Continuous cardiac monitoring if co-ingestants suspected

— Mental status checks q2–4 h if any encephalopathy concern

— Strict I/O; daily weights if AKI

— APAP undetectable

— AST and ALT improving and <1000 (some use normal); INR <2.0

— Patient clinically well, tolerating PO

— If not met → continue NAC at 6.25 mg/kg/h until met

— Primary care visit within 1–2 weeks for medication reconciliation and LFT recheck if recent injury

— Psychiatry within 7 days for intentional ingestion

— Hepatology referral only if persistent abnormalities at 4 weeks

— Read OTC labels for "acetaminophen" / "APAP" — count total daily dose across all products

— Avoid alcohol while taking APAP; never combine binge drinking with even therapeutic APAP

— Inform all prescribers of APAP-containing combination products

— In cirrhosis: APAP is preferred over NSAIDs (which cause bleeding, AKI, decompensation) at 2 g/day maximum

— APAP overdose is a sentinel event for health literacy, mental health access, and medication safety

— Consider referral to social work for resource needs, especially in repeated/staggered cases

Board pearl: In cirrhosis, APAP ≤2 g/day is safer than any NSAID — NSAIDs precipitate AKI, GI bleeding, and decompensation. Step 3 stems testing pain management in cirrhotics expect "low-dose acetaminophen" as the right answer.

Inpatient monitoring during NAC:

End-of-NAC criteria (do not stop until all met):

Post-discharge follow-up:

Counseling content:

Health systems issues:

Ethical, Legal, and Patient Safety Considerations

— A patient refusing NAC after a serious intentional overdose lacks capacity by definition if the refusal stems from active suicidality

— Treat over objection under emergency doctrine and involuntary hold (varies by state — typically 72-h psychiatric hold)

— Document capacity assessment carefully; involve psychiatry and risk management early

— Pediatric ingestion raising concern for neglect or abuse → mandatory CPS report

— Elder abuse / neglect in chronic supratherapeutic dosing scenarios → APS report in most states

— Suicide attempts are reportable to family/legal contacts per jurisdiction; document confidentiality discussions

— Lethal means restriction: counsel families to remove/secure all medications, firearms, sharps before discharge

— Document Columbia Suicide Severity Rating Scale or similar

— Suicide watch / 1:1 sitter while inpatient for any intentional ingestion

— Handoffs between ED → ICU → floor → psych → discharge are high-risk moments

— Medication reconciliation at every transition — ensure NAC continuation, taper plans, and home APAP removal

— Documented closed-loop communication to outpatient psychiatry; warm handoff if possible

— Many overdoses are unintentional from combination products

— FDA has limited single-tablet APAP content in combinations to ≤325 mg — counsel patients accordingly

— Disclose to family in life-threatening situations even if patient objects, under emergency exception

— Document carefully

Step 3 management: A 19-year-old refuses NAC after intentional ingestion. Correct action: place on emergency psychiatric hold, assess capacity (impaired by acute suicidality), and treat with NAC under emergency doctrine. Document the capacity determination, involve psychiatry and ethics/risk management. Respecting a "refusal" here is the wrong answer.

Informed consent and capacity:

Mandatory reporting:

Suicide risk and safety planning:

Transition-of-care risk (Step 3 favorite):

Health literacy and label confusion:

Confidentiality vs. duty to warn:

High-Yield Associations and Rapid-Fire Clinical Facts

— Toxic dose: ≥150 mg/kg or ≥7.5 g acute

— Max daily dose: 4 g healthy adult, 2 g cirrhotic

— Nomogram treatment line: 150 mcg/mL at 4 h

— Draw level: ≥4 hours post-ingestion

— NAC most effective: <8 hours post-ingestion

— IV NAC total: 300 mg/kg over 21 h (150 → 50 → 100)

— PO NAC: 140 → 70 mg/kg q4h × 17 doses

— King's College: pH <7.30 OR (INR >6.5 + Cr >3.4 + grade III/IV encephalopathy)

— Dialysis consideration: APAP >900 mcg/mL at 4 h

— AST > ALT, both >1000 → APAP (or ischemic hepatitis)

— #1 cause of ALF in US → APAP

— NAPQI = toxic metabolite; glutathione = detoxifier

— CYP2E1 induced by chronic alcohol, INH, isoniazid

— Anaphylactoid (not anaphylactic) reaction to NAC

— Centrilobular (zone 3) necrosis on histology

— Normal LFTs early ≠ safe

— Asymptomatic at 12 h ≠ safe

— Cirrhotic with ALT 2000 → think APAP, not alcoholic hepatitis

— Pregnant: treat normally, NAC is safe

— Rash during NAC: slow rate, do not stop

— Late presentation (>24 h): still give NAC if LFTs abnormal or APAP detectable

— APAP → NAC

— Iron → deferoxamine

— Methanol/ethylene glycol → fomepizole

— Benzos → flumazenil (rarely used)

— Opioids → naloxone

— TCA → sodium bicarbonate

Board pearl: If only ONE lab were available in a suspected overdose, draw the APAP level — it's cheap, fast, and identifies the most lethal and most treatable common ingestion.

The numbers to memorize:

Classic associations:

Trap-avoidance pearls:

Antidote pairings to remember in toxicology:

Board Question Stem Patterns

— "22-year-old woman 5 h after taking 30 tablets of extra-strength Tylenol; APAP 220 mcg/mL"

— Answer: Start IV N-acetylcysteine (plot on nomogram — above the 150 line)

— "Patient found down 'sometime yesterday' with empty Tylenol bottle; AST 4500, ALT 3800, INR 3.2"

— Answer: Start NAC empirically — nomogram does not apply; transaminitis confirms treatment indication

— "Alcoholic man taking 2 extra-strength Tylenol q4h for 3 days for tooth pain; AST 6000, ALT 4500"

— Answer: Start NAC — chronic supratherapeutic + induced CYP2E1; nomogram inapplicable

— "Patient took 25 tablets 2 hours ago, feels fine, normal exam"

— Answer: Activated charcoal now, draw APAP level at 4 h, then plot — do not be falsely reassured

— "26-week pregnant woman with 8-h APAP level above treatment line"

— Answer: IV NAC, same nomogram, OB consult; do not delay treatment

— "Flushing and wheezing 20 minutes into NAC infusion"

— Answer: Pause infusion, give diphenhydramine ± albuterol, resume at slower rate — do not stop NAC permanently

— "Day 3: jaundice, asterixis, INR 4.5, Cr 2.8, pH 7.28"

— Answer: Transfer to liver transplant center (meets/approaching King's criteria)

— "Medically cleared after intentional ingestion, wants to leave"

— Answer: Psychiatric evaluation before discharge; involuntary hold if needed

Key distinction: Step 3 stems test management decisions over time — recognizing when the nomogram applies vs. when to treat empirically is the single most tested concept in APAP toxicology.

Pattern 1 — The classic acute ingestion:

Pattern 2 — The unknown-time presentation:

Pattern 3 — The staggered ingestion:

Pattern 4 — Early asymptomatic:

Pattern 5 — The pregnant patient:

Pattern 6 — Anaphylactoid reaction:

Pattern 7 — When to transfer to transplant:

Pattern 8 — Discharge planning:

One-Line Recap

Acetaminophen toxicity is the leading US cause of acute liver failure; suspect it in any AST/ALT >1000 (AST>ALT), use the Rumack–Matthew nomogram only for single acute ingestions with known timing drawn ≥4 h post-ingestion, and give N-acetylcysteine — empirically when the nomogram doesn't apply — because NAC is safe, effective within 8 hours, and still beneficial out to and beyond 24 hours.

Diagnostic anchor: APAP level at ≥4 h plotted on Rumack–Matthew (treatment line 150 mcg/mL at 4 h); nomogram fails for staggered, unknown-time, or extended-release ingestions — in which case treat if APAP >10 mcg/mL or any transaminitis.

Therapeutic anchor: IV NAC 150 mg/kg over 1 h → 50 mg/kg over 4 h → 100 mg/kg over 16 h (21 h total); extend at 6.25 mg/kg/h if APAP still present, INR >2, or LFTs not improving; anaphylactoid reactions = slow, don't stop.

Escalation anchor: Transfer to a liver transplant center for INR >2.0, encephalopathy, acidosis (pH <7.30), or rising creatinine; King's College criteria define listing (pH <7.30 OR INR >6.5 + Cr >3.4 + grade III/IV encephalopathy).

Safety anchor: All intentional ingestions require psychiatric evaluation, capacity assessment, and lethal means restriction before discharge — treat over refusal under emergency doctrine when active suicidality impairs capacity, and always call Poison Control (1-800-222-1222).