Which feature best explains why paracetamol is an effective analgesic and antipyretic but has negligible anti-inflammatory activity at therapeutic doses?
- A It selectively inhibits COX-1 in platelets irreversibly
- B It competitively blocks bradykinin B2 receptors in inflamed tissue
- C Its action is largely central, with weak inhibition of peripheral COX in the presence of high peroxide concentrations at inflamed sites ✓
- D It inhibits phospholipase A2, preventing release of arachidonic acid only centrally
Correct answer: C. Its action is largely central, with weak inhibition of peripheral COX in the presence of high peroxide concentrations at inflamed sites
Explanation
Paracetamol acts mainly within the CNS, possibly through inhibition of a COX-2 variant and modulation of serotonergic descending pathways, producing analgesia and antipyresis. At peripheral inflammatory sites, high concentrations of peroxides generated by activated leucocytes inactivate its COX inhibitory effect, so prostaglandin synthesis in inflamed tissue is barely suppressed and anti-inflammatory activity is minimal. It does not inhibit platelet COX-1 irreversibly.
Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.