Paracetamol (acetaminophen) relieves pain and fever but has negligible anti-inflammatory activity at therapeutic doses. The accepted explanation for this profile is that it:

• A Inhibits COX-2 selectively in inflamed peripheral tissues
• B Acts as a peripheral opioid receptor agonist
• C Blocks both COX and lipoxygenase pathways equally throughout the body
• D Inhibits prostaglandin synthesis mainly in the central nervous system, where low peroxide tone permits its COX blockade ✓

Explanation

Paracetamol is a weak inhibitor of peripheral COX because high concentrations of peroxides generated at sites of inflammation overwhelm its effect. In the brain, peroxide tone is low, so it effectively blocks central prostaglandin synthesis, giving analgesic and antipyretic actions without meaningful peripheral anti-inflammatory activity. Option A is wrong because paracetamol is not a selective COX-2 inhibitor, and option B is wrong because it has no opioid action.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

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Written and medically reviewed by the StethoPrep medical team.