Classification
Analgesic
Antipyretic
Brand Names
Abenol®, Actimol®, Atasol®, Tylenol®
Indications
EMR: mild to moderate pain
ACP: mild to moderate pain and pyrexia
Contraindications
- Hypersensitivity to acetaminophen or any component of the formulation
- Severe alcoholic hepatitis or liver dysfunction with active alcohol consumption
- Acute liver injury
- Acetaminophen-induced liver disease
Adult dosages
EMR: analgesia ACP (analgesia and antipyresis):
- 500-1,000 mg PO (specifically, 15 mg/kg to a maximum of 1,000 mg)
- May repeat once after 4 hours
- 24-hour maximum: 3 g (3,000 mg)
- In patients with suspected or known liver dysfunction (e.g., advanced chronic liver disease or cirrhosis), the 24-hour maximum should be lowered to 1-2 g (1,000 mg - 2,000 mg)
- May be used concurrently with ibuprofen for analgesia
ACP only: follow analgesia dosing for antipyresis
Pediatric Considerations And Dosing
EMR: 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 once after 4 hours
- 24-hour maximum: 75 mg/kg or 1 g (1,000 mg)
- Do not exceed 5 doses in 24-hours in patients < 12 years of age
ACP only: follow analgesia dosing for antipyresis
Mechanism Of Action
Acetaminophen inhibits prostaglandin synthetase in the central nervous system, reducing pain and pyrexia.
Pharmacokinetics
Oral:
- Onset: 30 minutes
- Peak: 1-3 hours
- Duration: 4 hours
Intravenous:
- Onset: 15 minutes (matching rate of administration)
- Peak: 1 hour
- Duration: 4-6 hours (analgesia) and > 6 hours (antipyresis)
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 long-term use
Overdose
Toxicity may occur after a single dose of more than 7.5 g (adults) or 150 mg/kg (pediatrics).
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 pediatrics are at most 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.