Paracetamol Summary

Drug Class

  • Non-opioid analgesic
  • Antipyretic properties
  • No anti-inflammatory action
  • Similar efficacy to aspirin

Administration

  • Oral (most common)
  • Rectal
  • Intravenous

Special Populations

  • Pregnancy: Analgesic of choice
  • Breastfeeding: Suitable for use
  • Pediatrics: Weight-based dosing

Cautions

  • Chronic alcohol consumption
  • Chronic dehydration
  • Chronic malnutrition
  • Hepatic impairment
  • Weight <50 kg

Dosing

  • Adult: 500mg-1g Q4-6H
  • Max daily: 4 grams
  • Pediatric: 15mg/kg Q4-6H

Overdose

  • Hepatotoxicity >4g daily
  • Early: Nausea, vomiting, abdominal pain
  • Late: Liver failure, encephalopathy
  • Treatment: N-acetylcysteine

Risk Factors for Toxicity

  • Alcohol dependence
  • Pre-existing liver disease
  • Malnutrition
  • Liver enzyme inducing drugs

Paracetamol (Acetaminophen)

Non-opioid analgesic and antipyretic medication - Comprehensive clinical guide

Overview

Paracetamol is a widely used non-opioid analgesic with antipyretic properties. It is considered first-line for mild to moderate pain and is suitable for various patient populations including pregnant women and children.

Key Points: No anti-inflammatory properties • Safe in pregnancy • Maximum daily dose 4 grams • Risk of hepatotoxicity in overdose

Mechanism of Action

Pharmacological Class

  • Non-opioid analgesic
  • Similar efficacy to aspirin
  • Antipyretic properties
  • No anti-inflammatory properties

Proposed Mechanisms

  • Central inhibition of prostaglandin synthesis
  • Acts on COX enzymes in the CNS
  • Weak peripheral anti-inflammatory activity
  • Exact mechanism not fully understood

Routes of Administration

Oral

  • Most common route
  • Rapid absorption
  • Peak effect: 30-60 minutes

Rectal

  • Useful when oral route not possible
  • Slower absorption
  • Useful in pediatric patients

Intravenous

  • Rapid onset of action
  • Useful in hospital settings
  • More expensive formulation

Indications

Primary Indications

  • First-line for mild-to-moderate pain
  • Antipyretic for fever
  • Combination therapy for severe pain
  • Musculoskeletal pain
  • Headache and migraine

Special Populations

  • Pregnancy: Analgesic of choice
  • Breastfeeding: Suitable for use
  • Pediatrics: First-line analgesic/antipyretic
  • Elderly: Generally well tolerated

Pregnancy and Lactation

Pregnancy: Paracetamol is the analgesic of choice for women who are trying to conceive, or who are pregnant. It can be used at the standard dose at any stage of pregnancy.

Breastfeeding: Paracetamol is suitable for use during breastfeeding as only small amounts are excreted in breast milk.

Contraindications and Cautions

No absolute contraindications to the use of paracetamol, but certain conditions require caution and potential dose adjustment.

Special Precautions

Conditions Requiring Caution

  • Chronic alcohol consumption
  • Chronic dehydration
  • Chronic malnutrition
  • Hepatic impairment
  • People who weigh < 50 kg

Dose Adjustments

  • Reduce dose in hepatic impairment
  • Consider lower doses for low body weight
  • Extended dosing intervals in severe liver disease
  • Clinical judgment essential for dose adjustment

Side Effects

Adverse effects are rare with paracetamol when used at recommended doses.

Reported Adverse Effects

System Adverse Effects Frequency
Hematological Thrombocytopenia, agranulocytosis, leukopenia Very rare
Hepatic Elevated liver enzymes (with overdose) Dose-dependent
Allergic Skin rash, urticaria Rare
Renal Acute kidney injury (with overdose) Less common than hepatic

Note: There have been very rare reports of blood dyscrasias in people taking paracetamol, but it is not clear that these were directly caused by the paracetamol.

Overdose and Toxicity

Medical Emergency: Paracetamol doses greater than the maximum daily dose of 4 grams can lead to hepatotoxicity. In some people this may be fatal.

Risk Factors for Hepatotoxicity

Major Risk Factors

  • Alcohol dependence
  • Pre-existing liver disease
  • Malnutrition
  • Liver enzyme inducing drugs
    • Rifampicin
    • Carbamazepine
    • Phenytoin
    • Other enzyme inducers

Clinical Presentation of Overdose

Early Stage (0-24 hours)

  • Nausea and vomiting
  • Abdominal pain
  • Malaise, pallor, sweating
  • Symptoms usually settle within 24 hours

Latent Phase (24-72 hours)

  • Patient may appear well
  • Developing liver damage
  • Elevated liver enzymes
  • Right subcostal pain and tenderness

Hepatic Phase (3-4 days)

  • Liver damage peaks 3-4 days post-ingestion
  • Jaundice
  • Coagulopathy
  • Hepatic encephalopathy
  • Hypoglycemia
  • Cerebral edema
  • Possible multi-organ failure

Management of Overdose

Emergency Management Protocol
  1. Urgent hospital admission for significant overdose
  2. Activated charcoal if within 1-2 hours of ingestion
  3. Plasma paracetamol level at 4 hours post-ingestion
  4. N-acetylcysteine (NAC) therapy based on treatment nomogram
  5. Liver function monitoring
  6. Supportive care for liver failure if it develops

Dosing Guidelines

Adult Dosing

Route Dose Frequency Maximum Daily
Oral 500mg - 1g Every 4-6 hours 4 grams
Rectal 500mg - 1g Every 4-6 hours 4 grams
IV 1g Every 4-6 hours 4 grams

Pediatric Dosing

Age Dose Frequency Maximum Daily
1-3 months Consult specialist As directed As directed
3-12 months 60-120mg Every 4-6 hours 4 doses/24h
1-5 years 120-250mg Every 4-6 hours 4 doses/24h
6-12 years 250-500mg Every 4-6 hours 4 doses/24h
12+ years 500mg-1g Every 4-6 hours 4 grams

Important: Always use weight-based dosing in children when possible. Standard pediatric dose is 15mg/kg every 4-6 hours, maximum 75mg/kg/day.