Paracetamol Toxicity — Viva Defence

Long Case Viva Defence

The scenario

A 38-year-old unemployed man presents to the emergency department 14 hours after ingesting 24 g of paracetamol as a single dose during an alcohol binge. He has a background of chronic alcohol use (120 g per day), poor nutrition, and a recent relationship breakdown. He is drowsy but rousable and complains of right upper quadrant pain and nausea. On examination he is icteric, tender in the right upper quadrant, and has a flapping tremor. Investigations: AST 1200 U/L, ALT 980 U/L, INR 3.4, creatinine 180 micromol/L, arterial pH 7.32, arterial lactate 4.2 mmol/L, glucose 3.1 mmol/L, paracetamol level 90 mg/L, salicylate undetectable, ethanol 0.05 per cent. [1]

Opening statement (SASPOP)

"This is Mr D, a 38-year-old unemployed man presenting 14 hours after a 24 g single paracetamol overdose during an alcohol binge, with established stage 2 to 3 hepatotoxicity — transaminitis, coagulopathy, hypoglycaemia, mild encephalopathy and acute kidney injury — in a high-risk host with chronic alcohol use and malnutrition. His main problems are the paracetamol-induced acute liver injury (which I am treating with N-acetylcysteine and monitoring against the King's College Criteria), the acute kidney injury, his high-risk profile (CYP2E1 induction and glutathione depletion from chronic alcohol), the risk of alcohol withdrawal during admission, and the psychosocial context of deliberate self-harm. My priorities are to give NAC immediately, correct his hypoglycaemia and volume status, admit to a high-dependency bed, monitor for progression to acute liver failure, notify the transplant unit early given his high lactate, and manage his alcohol withdrawal and psychiatric risk once he is medically stable." [1]

Problem list (numbered, prioritised)

1. Single acute paracetamol overdose with established hepatotoxicity — 24 g (well above the 10 g threshold), 14 hours post-ingestion, with AST 1200 and INR 3.4.
2. High-risk patient — chronic alcohol use and malnutrition (CYP2E1 induction, glutathione depletion); managed on the 150 mg/L treatment line.
3. Approaching acute liver failure — coagulopathy, hypoglycaemia, high lactate, mild encephalopathy; close to but not yet meeting King's College Criteria.
4. Acute kidney injury (creatinine 180) — direct NAPQI tubular injury plus hepatorenal physiology.
5. Alcohol use disorder — withdrawal risk; malnutrition worsening recovery.
6. Deliberate self-harm and psychosocial crisis — relationship breakdown, unemployment; psychiatric assessment once stable. [1]

Integrated management plan

Pillar 1 — Immediate antidote and resuscitation: "I would start the 21-hour intravenous N-acetylcysteine regimen immediately — 150 mg/kg over 1 hour, then 50 mg/kg over 4 hours, then 100 mg/kg over 16 hours, totalling 300 mg/kg. Prescott established IV NAC as the treatment of choice, and it is a glutathione precursor that replenishes hepatic glutathione and allows conjugation of NAPQI [2]. I would not wait for any further testing — he is 14 hours in with established injury and a detectable level. I would give 10 per cent dextrose for his hypoglycaemia, check glucose hourly, and give cautious crystalloid for the volume depletion and to refine the lactate, then reassess."

Pillar 2 — Monitoring and risk stratification: "I would admit him to a high-dependency or ICU bed and repeat INR, AST, creatinine, lactate, pH and glucose every 4 to 6 hours. I would track the King's College Criteria continuously: for paracetamol-induced acute liver failure, transplant referral is indicated if either arterial pH below 7.3 after resuscitation, OR all three of INR above 6.5, creatinine above 300 and grade 3 to 4 encephalopathy [4]. His arterial lactate of 4.2 is above the 3.5 mmol/L early-admission threshold that Bernal showed identifies non-survivors a median of 6 hours before the formal criteria declare themselves [6], so I would notify the liver transplant unit now, before he formally meets the criteria."

Pillar 3 — Continuing NAC and managing adverse reactions: "Given his established hepatotoxicity I would continue NAC beyond 21 hours — the modified prolonged regimen at the third-bag rate — until the INR is below 1.3 and falling, the AST is falling, the paracetamol level is below 10 mg/L, and he is clinically well. Keays showed that IV NAC improves survival even after fulminant hepatic failure is established [5]. If he develops a reaction during the loading bag — urticaria, flushing, bronchospasm — I would stop the infusion, give chlorphenamine and hydrocortisone if moderate, and restart at a slower rate; these reactions are non-IgE-mediated and rate-related, occurring in up to 20 per cent, and do not contraindicate completing the course [7]."

Pillar 4 — Acute liver failure complications: "If his encephalopathy deepens I would manage it with lactulose, head-of-bed elevation, avoidance of sedatives, and intubation for grade 4. For cerebral oedema I would use mannitol or hypertonic saline to a sodium of 145 to 155. I would NOT routinely correct his INR with fresh frozen plasma — the INR is the prognostic marker that drives the transplant decision; I would give vitamin K 10 mg and reserve correction for active bleeding or before procedures. I would correct hypoglycaemia and hypophosphataemia, support renal failure with continuous renal replacement therapy if needed, and surveil for infection with cultures and a low threshold for antibiotics." [1]

Pillar 5 — Alcohol withdrawal and comorbidity: "I would start a symptom-triggered benzodiazepine regimen using CIWA-Ar scoring, give parenteral thiamine before any glucose to prevent Wernicke encephalopathy, correct potassium, magnesium and phosphate, and involve the addiction medicine and dietetics teams. His malnutrition worsens glutathione depletion and hepatic regeneration, so nutrition is part of the acute plan." [1]

Pillar 6 — Psychiatry and safety: "Once medically stable I would involve the psychiatric liaison team for risk assessment and a safety plan, address his alcohol use and the relationship breakdown, and arrange follow-up with mental health and addiction services. I would advise the pharmacist and general practitioner on limited dispensing and document the shared decisions." [1]

Probing questions the examiner would ask

Q: He is 20 minutes into the loading bag of NAC when he develops widespread urticaria and wheeze with oxygen saturation of 90 per cent. How do you respond? [1]

A: "This is a moderate-to-severe non-IgE-mediated rate-related reaction to NAC. I would stop the infusion immediately, give high-flow oxygen, an antihistamine (chlorphenamine 10 mg IV) and hydrocortisone 100 mg IV, and assess his airway and breathing. With oxygen desaturation and bronchospasm I would treat this as an anaphylactoid reaction and give intramuscular adrenaline 0.5 mg, with ICU involvement. Once the reaction has fully settled I would discuss with toxicology about re-challenging at a much slower rate, because the antidote is essential and most reactions are rate-related rather than true IgE allergy. Permanent cessation is reserved for genuine anaphylaxis that cannot be controlled, which is rare [7]."

Q: His INR rises to 7.5, creatinine to 310, and he progresses to grade 3 encephalopathy, with arterial pH 7.28. What do you do? [1]

A: "He now meets the King's College Criteria on both limbs — arterial pH below 7.3, and the full triad of INR above 6.5 with creatinine above 300 and grade 3 to 4 encephalopathy. Either alone is sufficient. I would urgently refer him to the liver transplant unit for assessment, continue NAC, manage his acute liver failure in ICU (cerebral oedema prophylaxis, renal replacement therapy, infection surveillance, no routine INR correction), and arrange the transplant workup — blood group, imaging, psychosocial assessment. The King's College Criteria were derived from the 1989 King's College cohort and remain the best-validated tool for paracetamol-induced acute liver failure [4]. A patient who meets the criteria and does not receive a transplant has a survival of around 20 per cent; with transplant, one-year survival exceeds 75 per cent."

Q: How does the lactate help you here? [1]

A: "Bernal showed that arterial lactate above 3.5 mmol/L on early admission, or above 3.0 mmol/L after fluid resuscitation, identifies non-survivors with similar accuracy to the King's College Criteria combined, but a median of 6 hours earlier — 4 hours versus 10 hours [6]. In a patient like Mr D whose lactate is 4.2 on admission, I would contact the transplant unit before he formally meets the criteria, to buy time for workup and transfer. The lactate is an early-warning adjunct to the criteria, not a replacement for them."

Q: How would your management differ if the ingestion had been staggered over three days rather than a single dose? [1]

A: "The nomogram would not apply — it is valid only for a single acute ingestion with a known time [1]. I would treat empirically with NAC because he has a detectable paracetamol level and AST elevation. Staggered overdose carries a worse prognosis despite smaller individual doses, and the King's College Criteria have reduced sensitivity in this group [8], so I would have a lower threshold for early transplant referral. Otherwise the supportive care — NAC, acute liver failure management, alcohol withdrawal prophylaxis — is the same."

Q: He tells you he took the overdose because his partner left him and he wants to die. How do you balance psychiatric risk with the transplant decision? [1]

A: "The acute medical treatment is not contingent on the psychiatric context — I treat the overdose and assess for transplant on purely medical grounds, because withholding treatment would be unethical and the suicide risk is treatable. The transplant team will involve psychiatry in the assessment, and a current suicide attempt is not in itself an absolute contraindication to transplant, though it requires careful evaluation of capacity, future risk, and the support available. Once he is medically stable I would ensure formal psychiatric risk assessment, a safety plan, and close follow-up. The principle is to treat the medical emergency now and address the psychiatric risk in parallel, not sequentially." [1]

Communication and shared decision-making

"I would speak with Mr D once he is rousable, and with his family with his consent, in plain language. I would explain that the paracetamol has injured his liver, that we are giving an antidote called N-acetylcysteine that works by replenishing a protective chemical in the liver, and that his chronic alcohol use has made him more vulnerable. I would be honest that the next 48 hours are critical and that we have involved the liver transplant team because his blood tests show serious injury. I would address his distress and his relationship breakdown directly, reassure him that the psychiatric team will support him, and involve his family in the safety plan. I would document the shared decisions and review them as his clinical picture evolves." [1]

Short Case Discussion — Acute Liver Failure Examination

Instruction: "Examine this patient's abdomen and assess for encephalopathy." [1]

Systematic examination routine

1. End of bed — observe for jaundice, drowsiness, agitation, asterixis, the rate and depth of breathing (Kussmaul of metabolic acidosis), and any monitoring or lines.
2. Hands and arms — liver flap (asterixis, a sign of grade 2 encephalopathy), palmar erythema, bruising and petechiae from coagulopathy, needle tracks, a flapping tremor, clubbing (not expected in acute failure), and peripheral stigmata of chronic alcohol use (palmar erythema, Dupuytren contracture).
3. Pulse and vital signs — tachycardia, blood pressure, temperature (sepsis), respiratory rate, oxygen saturation, and Glasgow Coma Scale.
4. Face and head — scleral icterus, conjunctival pallor, parotid enlargement and facial plethora of chronic alcohol use, fetor hepaticus (sweet musty breath of mercaptans).
5. Chest — gynaecomastia, spider naevi (above the nipple line), and pleural effusion; cardiac examination for a hyperdynamic circulation of sepsis or a cause of ischaemic hepatitis.
6. Abdomen — inspect for distension and caput medusae; palpate for tender hepatomegaly (stage 2 of paracetamol toxicity) or a small shrinking liver (established failure); assess for ascites (shifting dullness, fluid thrill); check for splenomegaly (suggests chronic rather than acute disease).
7. Neurological — grade the encephalopathy (grade 1 mild confusion and altered sleep; grade 2 drowsiness, disorientation, asterixis; grade 3 marked somnolence and confusion; grade 4 coma). Look for signs of cerebral oedema in grade 4 — hypertension with bradycardia (Cushing reflex), irregular breathing, pupillary changes.
8. Urine output — check the catheter; oliguria reflects acute kidney injury. [1]

Key physical signs the patient demonstrates (for this case)

• Icteric sclerae and mild jaundice
• A liver flap (asterixis) — grade 2 encephalopathy
• Right upper quadrant tenderness with a palpable tender liver edge
• Bruising on the arms from coagulopathy
• Fetor hepaticus
• Oliguria [1]

Presentation template

"I examined Mr D, a 38-year-old man, who is drowsy but rousable at the end of the bed, icteric, with a flapping tremor on sustained wrist extension consistent with grade 2 hepatic encephalopathy. He has fetor hepaticus. The pulse is 96 regular, blood pressure 110/70, he is afebrile, and his Glasgow Coma Scale is 14. The hands show a liver flap and several bruises. The chest shows no spider naevi or gynaecomastia. The abdomen reveals a tender palpable liver edge in the right upper quadrant with no ascites and no splenomegaly. The neurological examination is consistent with grade 2 encephalopathy. These findings, in the context of a paracetamol overdose 14 hours ago with an INR of 3.4 and AST of 1200, are consistent with stage 2 to 3 paracetamol-induced hepatotoxicity progressing toward acute liver failure. I would monitor the encephalopathy grade and the INR against the King's College Criteria for transplant referral." [1]

Discussion questions

Q: How do you grade hepatic encephalopathy, and why does the grade matter? [1]

A: "I use the West Haven classification: grade 1 is mild confusion, euphoria or anxiety, and a shortened attention span with altered sleep rhythm; grade 2 is lethargy or apathy, disorientation, and asterixis; grade 3 is marked somnolence or semi-stupor, responsive to stimuli, with gross disorientation; grade 4 is coma with or without response to painful stimuli. The grade matters because it is a prognostic marker and a component of the King's College Criteria — grade 3 to 4 encephalopathy with INR above 6.5 and creatinine above 300 is a transplant criterion. Grade 3 to 4 also carries the risk of cerebral oedema, the leading cause of early death in acute liver failure, which is why these patients need ICU and often intracranial pressure control." [1]

Q: Why is the necrosis centrilobular? [1]

A: "Because the hepatocytes around the central vein (zone 3 of the acinus) have the highest CYP2E1 activity — the enzyme that generates the toxic metabolite NAPQI — and the lowest oxygen tension, making them the most vulnerable to NAPQI adduct formation and oxidative injury. The periportal hepatocytes (zone 1) are relatively spared, which is why the liver can regenerate even after massive injury. On histology you see a sharp band of coagulative necrosis around the central veins with a preserved periportal rim [7]."

Q: Why do you not routinely correct the INR with fresh frozen plasma in acute liver failure? [1]

A: "Because the INR is the single most important prognostic marker and a component of the King's College Criteria. Correcting it with fresh frozen plasma destroys that prognostic information and may mask progression to a transplant-triggering level, delaying referral. I would give vitamin K 10 mg to correct any reversible vitamin K deficiency, and reserve fresh frozen plasma or prothrombin complex concentrate for active bleeding or immediately before invasive procedures. The coagulopathy of liver failure is also more complex than the INR suggests — these patients are often rebalanced because they lose both procoagulant and anticoagulant factors, and they are not auto-anticoagulated in the way the INR suggests." [1]

Q: When would you give activated charcoal, and when is it futile? [1]

A: "Activated charcoal is most effective within 1 to 2 hours of ingestion, when the drug is still in the stomach, and is given as 50 g (1 g/kg in children) if the airway is protected. Beyond 2 hours the benefit falls sharply because most of the drug has been absorbed, though it can still be considered for a massive ingestion, a staggered overdose, or a sustained-release or delayed-absorption formulation. It is futile in a patient who presents at 14 hours, as in Mr D, because the drug has long since been absorbed. Charcoal does not significantly reduce the efficacy of subsequent intravenous NAC." [1]

Q: What is the role of arterial lactate in this patient's prognosis? [1]

A: "Bernal showed that arterial lactate above 3.5 mmol/L on early admission, or above 3.0 mmol/L after fluid resuscitation, predicts non-survival with accuracy similar to the King's College Criteria combined, but declares itself a median of 6 hours earlier — 4 hours versus 10 hours [6]. Mr D's lactate of 4.2 on admission is above that threshold, so I would contact the transplant unit before he formally meets the criteria, to allow time for workup and transfer. The lactate is an early-warning adjunct that complements the criteria, not a replacement."