**Question:** Which of the following is/are cyclo–oxygenase inhibitors :

A. Celecoxib
B. Naproxen
C. Ibuprofen
D. Aspirin

**Core Concept:** Cyclooxygenase (COX) enzymes are responsible for the conversion of arachidonic acid to prostaglandins, which are involved in inflammation, pain, and fever. There are two main isoforms: COX-1 and COX-2.

**Why the Correct Answer is Right:** COX-2 inhibitors selectively target the COX-2 enzyme, reducing inflammation and pain without affecting gastrointestinal protection provided by COX-1. Celecoxib and naproxen are selective COX-2 inhibitors.

Diclofenac is a non-selective COX inhibitor, meaning it inhibits both COX-1 and COX-2, and can cause gastrointestinal side effects due to the inhibition of COX-1.

Corticosteroids like prednisolone and hydrocortisone are anti-inflammatory agents but not COX inhibitors. They work by inhibiting the production of pro-inflammatory cytokines and leukotrienes.

**Why Each Wrong Option is Incorrect:**

A. Celecoxib is a selective COX-2 inhibitor, not a non-selective COX inhibitor like naproxen.
B. Diclofenac is a non-selective COX inhibitor, not a selective COX-2 inhibitor like celecoxib and naproxen.
C. Corticosteroids are anti-inflammatory agents, not COX inhibitors. They work through different mechanisms as mentioned above.
D. Aspirin is a salicylic acid derivative that irreversibly inhibits the platelet cyclooxygenase enzyme (COX-1 and COX-2), not a selective COX-2 inhibitor.

**Clinical Pearl:** Selective COX-2 inhibitors are used for treating inflammatory conditions to reduce side effects associated with non-selective COX inhibitors like diclofenac. However, non-selective COX inhibitors like aspirin have antipyretic, analgesic, and anti-inflammatory effects.

**Correct Answer Line:** D. Aspirin is a selective COX-1 inhibitor, not a selective COX-2 inhibitor. It is an irreversible inhibitor of cyclooxygenase enzymes (COX-1 and COX-2) responsible for the production of prostaglandins.

Aspirin is commonly used for its antiplatelet effects, which are not related to COX inhibition. The misconception that aspirin is a selective COX-2 inhibitor is a common one, but it has been debunked.