Simple analgesics · Pain & inflammation
Acetaminophen
paracetamol · Tylenol®(brand names vary by market)
The first-line analgesic whose safety is a ceiling, not a property.
Also: capsule, oral liquid, suppository, infusion
Mechanism
Central COX inhibition (mechanism incompletely characterized): analgesic and antipyretic with minimal anti-inflammatory or antiplatelet action.
Indications
- Mild-moderate pain, first line
- Fever
Formulations
Dosing concepts
The ceiling
Maximum daily dose (commonly 4 g in healthy adults, lower in liver disease, low weight, chronic alcohol use) is the entire safety story; toxicity is a dose phenomenon.
Hidden sources
Combination cold products and opioid combinations stack acetaminophen invisibly; totalling all sources is the pharmacist's counter reflex.
Concepts, not prescribing instructions. Practice numbers live in current references and local protocols.
Pharmacokinetics
- Bioavailability
- ~88%
- Half-life
- ~2-3 h
- Elimination
- hepatic: Glucuronidation/sulfation; the small NAPQI fraction via CYP2E1 is what kills in overdose when glutathione runs out
Adverse effects
- Hepatotoxicity in overdoseseriousThe classic delayed injury: fine for a day, then transaminases in the thousands.
- Rare rashcommon
Contraindications & precautions
Contraindications
- Severe active liver failure
Precautions
- Chronic liver disease
- Chronic alcohol use
- Low body weight and frailty
- All combination products (count total daily intake)
Interactions
Monitoring
Total daily intake across all products
The overdose that happens by accumulation
Counselling points
- Keep to the stated maximum in 24 hours, counting every product that contains it. Many cold and pain products do.
- In overdose, get help immediately even if you feel fine; the danger is delayed.
Clinical pearls
- N-acetylcysteine works by restocking glutathione. The antidote is a substrate, which is why timing matters.
References & review
- Acetaminophen product monograph (consult the current version for your market) (monograph)
- Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. (reference-work)
Last reviewed 2026-08-15 · jurisdiction: global · drug information changes; verify against current references before practice use.