Understanding Paracetamol (Acetaminophen): A Comprehensive Guide


Paracetamol, commonly known as acetaminophen, is a widely used medication for managing pain and fever. Whether you're a healthcare professional or simply curious about this over-the-counter drug, let's delve into the essential aspects of paracetamol.


1. Key Parameters


- Bioavailability (F): Paracetamol is rapidly absorbed in the gastrointestinal tract, with an oral bioavailability ranging from 85% to 98%.

- Volume of Distribution (Vd):

  - Pediatrics: 0.7 – 1.2 L/kg

  - Adults: 0.7 – 1 L/kg

- Protein Binding: Approximately 10% - 25% (increases at toxic doses).


2. Metabolism


- Paracetamol undergoes hepatic metabolism via conjugation with glucuronide, sulphate, and oxidation (mainly through CYP2E1).

- The toxic metabolite, N-acetyl-p-benzoquinone imine (NAPQI), is formed via oxidative pathways and is conjugated with glutathione.



3. Indication and Toxic Ranges


- Minimum toxic doses:

  - Pediatric: 150 mg/kg (200 mg/kg in healthy children aged 1 – 6 years)

  - Adults: 7.5 – 10 g


4. Dosage Guidelines


- Pediatric:

  - Oral: 10 – 15 mg/kg/dose every 4 – 6 hours (maximum: 75 mg/kg/day).

  - Rectal: Varies based on age and weight.

- Adult:

  - Oral: 650 mg – 1000 mg every 4 – 6 hours (maximum: 4 g/day).

  - Rectal: Similar dosing as oral.


5. Monitoring and Nomogram


- Rumack-Matthew Nomogram:

  - Predicts hepatotoxicity risk based on paracetamol plasma concentration.

  - Obtain concentrations 4 – 18 hours post-ingestion for reliable results.


6. Phases of Paracetamol Poisoning


1. Phase 1 (0.5 – 24 hours): Initial symptoms.

2. Phase 2 (18 – 72 hours): Right upper quadrant pain, tachycardia, hypotension.

3. Phase 3 (72 – 96 hours): Hepatic phase with jaundice and coagulopathy.

4. Phase 4 (4 days – 3 weeks): Recovery or multi-organ failure.


7. Management and Antidote (NAC)


- Activated Charcoal: Administered within 1 hour of ingestion.

- N-Acetylcysteine (NAC):

  - Precursor to glutathione, reducing toxicity.

  - Start immediately (within 8 hours) for probable hepatic toxicity.

  - Monitor serum paracetamol concentration.



Case Discussion: A Life Saved


Let's consider the case of patient SL, an 18-year-old with a body weight of 52 kg. The patient presented with suicidal paracetamol poisoning, having ingested 962 mg/kg (10 empty blister packs of 500 mg each). The blood paracetamol level was measured at 296.74 mg/L (4 hours post-ingestion).


- Treatment:

  - Following the Rumack-Matthew nomogram, the level indicated toxicity.

  - Intravenous N-Acetylcysteine (NAC) was initiated promptly.

  - Over the next 24 hours, the patient's liver enzymes improved, and clinical symptoms resolved.


Remember, timely intervention and understanding paracetamol toxicity are critical for positive outcomes. Seek medical help immediately in case of overdose or toxicity. 🌟