**Core Concept:** Drug-induced colitis is a clinical entity characterized by inflammation of the colon caused by certain medications or drugs. The underlying mechanism involves toxic effects of these drugs on the colonic mucosa, leading to symptoms and signs consistent with colitis.

**Why the Correct Answer is Right:** Colitis is caused by the drug **Arava (leflunomide)**, which is an immunosuppressive agent used in the treatment of autoimmune diseases like rheumatoid arthritis. However, its use is associated with the development of colitis due to its inhibition of pyrimidine synthesis, leading to mucosal damage and inflammation.

**Why Each Wrong Option is Incorrect:**

A. **Azathioprine (Imuran)** is another immunosuppressive drug that has been implicated in inducing colitis, but it is not as common as Arava. It also inhibits pyrimidine synthesis, causing mucosal damage and inflammation.

B. **NSAIDs (Nonsteroidal Anti-inflammatory Drugs)** typically cause enteric complications like gastritis, peptic ulcers, and rarely, colitis. While they can exacerbate pre-existing colitis, they are not directly associated with drug-induced colitis.

C. **Antacids** do not cause colitis as they primarily target the stomach and duodenum.

D. **Anti-diabetic medications** like metformin and sulfonylureas do not directly cause colitis, although they may exacerbate pre-existing inflammatory conditions.

**Clinical Pearl:** Drug-induced colitis is a rare but serious adverse effect of immunosuppressive drugs like Arava. It is essential for physicians to be aware of this complication when prescribing these medications and monitor patients for symptoms. In suspected cases, discontinuation of the causative drug and supportive treatment may help improve the patient's condition.