A 28-year-old woman is brought to the emergency department 6 hours after ingesting approximately 15 g of paracetamol in a suicide attempt. She is currently asymptomatic with normal vital signs. Physical examination is unremarkable. Blood investigations show: AST 45 U/L, ALT 52 U/L, bilirubin 0.9 mg/dL, INR 1.0, serum paracetamol level 180 µg/mL. What is the most appropriate next step in management?

Explanation

## Clinical Assessment of Paracetamol Poisoning ### Timing and Nomogram Use **Key Point:** The Rumack-Matthew nomogram is the gold standard for determining NAC eligibility in paracetamol overdose. It plots serum paracetamol concentration against time since ingestion to stratify risk. At **6 hours post-ingestion**, the treatment threshold on the standard nomogram is approximately **150 µg/mL** (some sources cite 150–200 µg/mL depending on the line used, but the widely accepted "probable toxicity" treatment line at 6 hours is ~150 µg/mL per Rumack-Matthew). ### Interpretation of This Case - **Time since ingestion:** 6 hours - **Serum paracetamol level:** 180 µg/mL - **Nomogram position:** At 6 hours, a level of 180 µg/mL falls **above the treatment line** (~150 µg/mL at 6 hours) → NAC is indicated - **Activated charcoal:** Activated charcoal is generally recommended only within **1–2 hours** of ingestion (maximum up to 4 hours in some protocols). At 6 hours post-ingestion, activated charcoal is **not indicated** as absorption is essentially complete. - **Current liver function:** Normal (AST, ALT, bilirubin, INR all within normal limits) — this does not change the decision; NAC is preventive, not reactive. ### Why Option A (Administer NAC Immediately) Is Correct **High-Yield:** Since the patient presents at 6 hours with a paracetamol level above the nomogram treatment threshold, **immediate NAC administration** is the correct next step. There is no role for activated charcoal at this time point (absorption is complete), and waiting for LFT abnormalities before starting NAC is dangerous — NAC is most effective when started within 8–10 hours of ingestion. ### Why Option B Is Incorrect **Clinical Pearl:** Option B (activated charcoal followed by NAC if indicated by nomogram) is incorrect because: 1. Activated charcoal is not beneficial at 6 hours post-ingestion — paracetamol is already absorbed. 2. The nomogram has already been applied (level 180 µg/mL at 6 hours is above the treatment line), so NAC should be started **immediately** without further delay. ### NAC Dosing Regimen (per KD Tripathi / Harrison's) The standard IV NAC protocol: 1. **Loading dose:** 150 mg/kg IV over 1 hour 2. **Second dose:** 50 mg/kg IV over 4 hours 3. **Third dose:** 100 mg/kg IV over 16 hours ### Mechanism of NAC NAC prevents hepatotoxicity by: - Replenishing hepatic glutathione stores depleted by the toxic metabolite NAPQI - Facilitating paracetamol conjugation and elimination - Providing direct antioxidant protection ### Monitoring During NAC Therapy - Repeat INR, bilirubin, and transaminases at 24 and 48 hours - Monitor for anaphylactoid reactions (flushing, rash, bronchospasm) — more common with IV NAC - Continue NAC even if initial liver function is normal; hepatotoxicity may develop over 48–72 hours **Warning:** Do not wait for evidence of liver dysfunction to initiate NAC. The nomogram-based approach is **preventive**, not reactive. (Reference: Harrison's Principles of Internal Medicine, 21st ed.; KD Tripathi Essentials of Medical Pharmacology, 8th ed.)