Last updated: October 29, 2014

Trade Names: Include Acephen, Aspirin-free Anacin, Tylenol, Tylenol Arthritis

Synonyms: Paracetamol

Drug Class: Analgesic/antipyretic

Capsules: 325 and 500 mg (extra strength)
Tablets: 120, 160, 325, 500 mg; 650 mg (extended-release)
Suppositories: 80, 120, 325, 650 mg
Elixir, suspension, liquid, or syrup: 100 mg/mL and 160 mg/5 mL

Dose: Adults, 1–3 g/day in three to four divided doses; do not exceed total daily dose of 4 g/day from all sources. Some experts believe the maximum daily dose of acetaminophen should be limited to 3 g/day.

Indications: Pain, musculoskeletal pain, headache, fever; less likely to cause GI ulceration than NSAIDs

Mechanism of Action: Uncertain; may inhibit COX-2 and central prostaglandin synthesis

Contraindications: Hypersensitivity to acetaminophen

Precautions: Concomitant alcohol use, liver disease and fasting may increase the risk of acetaminophen hepatotoxicity. Avoid or use lower doses with caution in liver disease (usually <2 g/day). Avoid concomitant alcohol. May cause severe hepatotoxicity in overdose. Patients must avoid self-medication with OTC preparations that may also contain acetaminophen.

Pregnancy Risk: B

Adverse Effects: Rarely causes allergy, Stevens-Johnson syndrome,  rash, or agranulocytosis. Hepatotoxicity is rare at therapeutic doses. Overdose (usually >8 g/day) causes delayed (48–72 hours) and potentially fatal hepatotoxicity. Controversial evidence links chronic use to increased risk of renal impairment.

Drug Interactions
Alcohol: Increases risk of hepatotoxicity
Warfarin: Acetaminophen (>2 g/day) may increase anticoagulant effect Barbiturates, carbamazepine, hydantoins, and sulfinpyrazone: May increase hepatotoxicity of acetaminophen

Patient Instructions: Do not exceed prescribed dose; do not take additional OTC or prescription medications that contain acetaminophen; do not drink alcohol.

Clinical Pharmacology: Rapid complete oral absorption; 95% metabolized in the liver (mainly conjugation). Duration of action is 4–6 hours. With overdose, a hepatotoxic metabolite accumulates.

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