**Question:** Treatment of choice in intractable ulcerative colitis

**Core Concept:** Ulcerative colitis (UC) is a subtype of inflammatory bowel disease (IBD) characterized by chronic, nonspecific inflammation of the colon. The goal of treatment is to induce and maintain remission, improve quality of life, and prevent complications.

**Why the Correct Answer is Right:**

The correct answer, **D. Tacrolimus**, is a potent calcineurin inhibitor used for the treatment of various immune-mediated disorders, including intractable ulcerative colitis. Tacrolimus works by suppressing the immune response, reducing inflammation, and preventing mucosal damage. In the context of UC, it helps in inducing and maintaining remission, reducing symptoms, and improving the quality of life for patients.

**Why Each Wrong Option is Incorrect:**

A. **Methotrexate (MTX)** is an anti-proliferative drug primarily used in rheumatology for autoimmune disorders. While it has been tried in UC, its efficacy in the treatment of UC is limited, and its use should be avoided due to potential severe side effects.

B. **Azathioprine (AZA)** is an immunosuppressive agent that works by inhibiting DNA synthesis and cell proliferation, useful in the treatment of autoimmune disorders. However, its efficacy in UC is less than that of tacrolimus and its use should be avoided due to the risk of myelosuppression and viral reactivation.

C. **Mesalamine (5-ASA)** is a local anti-inflammatory drug used for mild to moderate UC. It is an effective treatment for mild to moderate UC but is not as effective in severe cases like tacrolimus.

**Clinical Pearl:**

In intractable ulcerative colitis, tacrolimus is the preferred treatment option due to its superior efficacy in inducing and maintaining remission, reducing symptoms, and improving patient quality of life. However, it is essential for physicians to be aware of the contraindications and potential side effects associated with tacrolimus.

When selecting a treatment option for UC, consider the disease severity, patient comorbidities, and potential risks and benefits of each treatment modality. Always consult with a medical expert before making a treatment decision for an intractable case of UC.