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.