What is the primary mechanism of action of NSAIDs?

• A. Inhibit dihydrofolate reductase
• B. Block H1 histamine receptor
• C. Inhibit 5-lipoxygenase
• D. Inhibit cyclooxygenase (COX-1 and COX-2), reducing prostaglandin synthesis

Answer: (D)

NSAIDs work by inhibiting cyclooxygenase enzymes (COX-1 and COX-2), which blocks the conversion of arachidonic acid into prostaglandins. Prostaglandins promote inflammation, sensitize nerves to pain, and raise body temperature during fever; lowering their production reduces pain, swelling, and fever. The other mechanisms belong to different drug classes: inhibiting dihydrofolate reductase is seen with certain chemotherapy agents; blocking H1 receptors is how antihistamines work; inhibiting 5-lipoxygenase reduces leukotriene production, another inflammatory pathway not the primary target of NSAIDs.