Which of the following medications is not a propionic acid?

Celecoxib is the correct choice because it belongs to a different class of medications known as COX-2 inhibitors, rather than being a propionic acid derivative. The propionic acid class includes nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, naproxen, and ketoprofen, all of which have similar chemical structures and mechanisms of action that involve blocking the cyclooxygenase enzymes (COX-1 and COX-2). In contrast, celecoxib specifically inhibits only the COX-2 enzyme, which is primarily responsible for inflammation while sparing COX-1, which protects the stomach lining and supports platelet function. This distinction is essential for understanding both the therapeutic effects and potential side effects associated with these medications.