Acetaminophen
Non-opioid analgesic and antipyretic for mild to moderate pain and fever
Indications
- PO only
Contraindications
- Hypersensitivity to acetaminophen or any component of the formulation
- Severe hepatic impairment or severe active liver disease
- Do not administer if acetaminophen has been given within the past 4 hours (from all sources), or if total acetaminophen intake within the last 24 hours exceeds the daily maximums (refer below for maximums).
- Do not administer acetaminophen if overdose is suspected, indicated by symptoms such as nausea, vomiting, or right upper quadrant pain
Cautions
- Hepatic impairment, heavy alcohol use, chronic malnutrition, and hypovolemia
Adult Dosages
From all sources and all routes of administration: 4,000 mg
Analgesia
- 500 - 1,000 mg PO
- May repeat once after 4 hours
- In patients with suspected or known liver dysfunction (e.g., advanced chronic liver disease, cirrhosis, heavy alcohol use) or malnutrition, the 24-hour maximum should be lowered to 2,000 mg.
- May be used concurrently with ibuprofen for analgesia
Pediatric Considerations
To be filled in.
Adverse Effects
Adverse reactions are uncommon with short-term use of acetaminophen.
- Nausea and vomiting can occur with IV formulation.
- Hypotension has been reported with IV infusion, particularly in critically ill patients. Monitor baseline BP and then q15min x 3.
- Rash and hives are rarely reported, but can occur.
Additional Information
Mechanism of Action
Acetaminophen inhibits prostaglandin synthetase in the central nervous system, reducing pain and pyrexia.
Pharmacokinetics
| Route | Onset | Peak | Duration |
|---|---|---|---|
| Oral: | 30 minutes | 1-3 hours | 4 hours |
| Intravenous: | 15 minutes (matching rate of administration) | 1 hour | 4-6 hours (analgesia) and > 6 hours (antipyresis) |
Overdose
Toxicity may occur after a single dose of more than 7.5 g (adults) or 150 mg/kg (pediatrics). Clinical findings of toxicity include nausea, vomiting, and/or right upper quadrant pain.
Warnings 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. Chronic acetaminophen use can impact INR levels, potentially affecting patients taking warfarin.