What is the Pharmacokinetics of Acetaminophen?

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Acetaminophen Pharmacokinetics

Absorption

Bioavailability

Well absorbed following oral administration, with peak plasma concentration attained within 10–60 minutes (immediate-release preparations) or 60–120 minutes (extended-release preparations).a

Poor or variable absorption following rectal administration; considerable variation in peak plasma concentrations attained; time to reach peak plasma concentration is substantially longer than after oral administration.

Food

Food may delay absorption following administration as extended-release tablets.148

Distribution

Extent

Rapidly distributed to most body tissues.a Crosses placenta and is distributed into breast milk.198

Plasma Protein Binding

25%.a

Elimination

Metabolism

Metabolized principally by sulfate and glucuronide conjugation; 226 small amounts (5–10%) oxidized by CYP-dependent pathways (mainly CYP2E1 and CYP3A4) to a toxic metabolite, N-acetyl-p-benzoquinoneimine (NAPQI).226 NAPQI is detoxified by glutathione and eliminated; any remaining toxic metabolite may bind to hepatocytes and cause cellular necrosis.121 226

Elimination Route

Mainly excreted in urine as conjugates.

Half-life

1.25–3 hours.