A 65-year-old man with a history of myocardial infarction and chronic stable angina is on low-dose aspirin. His physician plans to prescribe ibuprofen for osteoarthritis. What is the clinically significant drug interaction between aspirin and ibuprofen?
- A Ibuprofen inhibits CYP2C9, increasing aspirin levels and bleeding risk
- B Aspirin displaces ibuprofen from albumin, causing ibuprofen toxicity
- C Ibuprofen occupies the COX-1 active site reversibly, preventing aspirin from accessing and irreversibly acetylating it ✓
- D Both drugs synergistically inhibit COX-2, causing renal failure
Correct answer: C. Ibuprofen occupies the COX-1 active site reversibly, preventing aspirin from accessing and irreversibly acetylating it
Explanation
Ibuprofen binds reversibly to the COX-1 channel and can physically block aspirin from reaching its acetylation site (Ser530) on platelet COX-1. If ibuprofen is taken before aspirin, it can abolish aspirin's irreversible antiplatelet effect. This interaction is clinically significant because it can negate the cardioprotective benefit of low-dose aspirin. Current guidelines recommend taking aspirin at least 30 minutes before ibuprofen or 8 hours after.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 13th ed.
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