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Clinical Practice Guidelines
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Acetaminophen

Classification

Analgesic and antipyretic

Indications

PCP and higher: treatment of mild to moderate pain

ACP: reduction of fever

Contraindications

Severe hepatic impairment or liver disease
Acetaminophen-induced liver disease
Hypersensitivity to acetaminophen, or any component of the formulation

Adult dosages

PCP (analgesia) and ACP (analgesia and antipyresis):

500 - 1,000 mg PO
May repeat this dose once after 4 hours
24 hour maximum: 4,000 mg
- In patients with liver disease, the 24 hour maximum should be lowered to 1,000-2,000 mg
May be used concurrently with ibuprofen for analgesia

ACP only: follow analgesia dosing for antipyresis

Pediatric Considerations And Dosing

PCP (analgesia) and ACP (analgesia and antipyresis):

Follow weight-based dosing.
< 30 kg: 15 mg/kg PO (use liquid preparation)
30-50 kg: 500 mg PO (may use liquid preparation or tablets, depending on patient ability)
> 50 kg: 500-1,000 mg PO
- May repeat this dose once after 4 hours
- 24 hour maximum: 75 mg/kg or 1,000 mg
  - Do not exceed 5 doses in 24 hours in patients under the age of 12
ACP only: follow analgesia dosing for antipyresis

Mechanism Of Action

Acetaminophen inhibits prostaglandin synthetase in the central nervous system, reducing pain and fever.

Pharmocokinetics

Completely and rapidly absorbed from the gastrointestinal tract.

Onset: 30 minutes to 1 hour
Peak: 1-3 hours
Duration: 3-8 hours

Metabolism takes place in the liver, and acetaminophen is excreted in the urine.

Adverse Effects

Adverse reactions are uncommon with short-term use of acetaminophen. Rash and hives are rarely reported, but can occur. Constipation can develop with longer term use.

Overdose

Toxicity may occur after a single dose of more than 7,500 mg (adults) or 150 mg/kg (children).

Warning And Precautions

Acetaminophen is the leading cause of serious liver injury in Canada. Patients with pre-existing liver disease (regardless of underlying cause), chronic users of acetaminophen, and children are most at risk. Acetaminophen is a component of many over-the-counter medications, and patients may inadvertently be consuming much higher doses than expected. Paramedics must ensure that a complete medication history is obtained prior to the administration of acetaminophen, including over-the-counter preparations.

Drug Interactions

Alcohol may potentiate acetaminophen’s hepatoxic effects.