Known brand names include Tylenol, Mapap, and Panadol.
A pain reliever and fever reducer, taken by mouth over the counter or given IV in the hospital. Too much, including from combination products that also contain it, can cause severe liver damage.
Labeled use. Minor aches and pains (oral OTC), and mild to moderate pain from age 2 (IV).
Add-on therapy. IV, together with opioid analgesics for moderate to severe pain.
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First choice for mild pain and fever when an NSAID is a poor fit, such as with bleeding risk, anticoagulants, peptic ulcer disease, kidney disease, or late pregnancy, because it does not affect platelets, the stomach lining, or the kidneys the way NSAIDs do. It has little anti-inflammatory effect. IV acetaminophen reduces opioid needs after surgery.
The precise mechanism is not established; analgesic and antipyretic effects are thought to be mainly central. It has no meaningful effect on platelet aggregation or bleeding time. The liver clears it by glucuronide and sulfate conjugation, plus CYP2E1 oxidation to the reactive metabolite NAPQI, which glutathione normally detoxifies.
The labels do not describe a narrow therapeutic index or direct dosing by measured blood levels. Serum levels are used only to judge overdose.
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Doses come from the FDA label. Study tool, not for clinical decisions.
Severe renal impairment (creatinine clearance 30 mL/min or less): longer dosing intervals and a lower total daily dose may be needed.
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Contraindicated in severe hepatic impairment or severe active liver disease. Use with caution in other hepatic impairment, where a lower total daily dose may be needed.
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IV: risk of medication errors and hepatotoxicity. Dosing errors, such as confusing mg with mL, weight-based errors under 50 kg, or misprogrammed pumps, can cause accidental overdose and death. Acetaminophen has caused acute liver failure, sometimes leading to transplant or death, mostly at doses above the daily maximum and often from more than one acetaminophen product.
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N-acetylcysteine (NAC), given as early as possible after a suspected overdose. Draw a serum acetaminophen level no sooner than 4 hours after an oral ingestion and plot it on the Rumack-Matthew nomogram; give the full NAC course if the level is above the lower treatment line. Check liver tests at the start and every 24 hours.
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Large studies of oral acetaminophen in pregnancy have not shown a clear link to birth defects, miscarriage, or poor maternal or fetal outcomes, though they cannot rule out all risk. OTC users should ask a health professional before use.
Passes into milk at levels similar to plasma; infant exposure is low, about 1% to 2% of the weight-adjusted maternal dose. One infant rash was reported. Weigh breastfeeding benefits against maternal need.
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IV: effective for pain from age 2; not shown effective for pain under 2. For fever, studied down to premature neonates born at 32 weeks or later. Doses are weight-based. OTC caplets: children under 12 should ask a doctor.
No overall differences in safety or effectiveness were seen in older adults, though greater sensitivity in some cannot be ruled out.
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