Aspirin differs from ibuprofen in its action on cyclooxygenase because aspirin:

• A Reversibly competes with arachidonic acid at the active site
• B Allosterically activates the peroxidase function of COX
• C Irreversibly acetylates a serine residue of the enzyme ✓
• D Inhibits only the inducible COX-2 isoform

Explanation

Aspirin transfers its acetyl group to a serine residue in cyclooxygenase, causing irreversible inhibition. The effect lasts for the lifetime of the platelet, roughly 7 to 10 days, since platelets lack nuclei and cannot resynthesize the enzyme. Ibuprofen binds reversibly and competitively. This irreversible action is the basis of aspirin's prolonged antiplatelet effect and of the interaction where ibuprofen taken before aspirin blocks access to the active site.

Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.