**Core Concept**
Steroid-resistant lepra reactions, also known as Type 2 lepra reactions, are a complication of leprosy characterized by inflammation and nerve damage. The treatment of these reactions is challenging, and alternative medications are often required to manage symptoms.

**Why the Correct Answer is Right**
The correct answer is a corticosteroid-sparing agent used to treat lepra reactions. Ketotifen, a mast cell stabilizer, has been found to be effective in managing Type 2 lepra reactions, particularly in patients who are unresponsive to corticosteroids. Ketotifen works by inhibiting the release of histamine and other mediators from mast cells, thereby reducing inflammation and nerve damage.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not a commonly used medication for lepra reactions.
**Option B:** This option is incorrect because it is primarily used for managing allergies and does not have a role in treating lepra reactions.
**Option C:** This option is incorrect because it is not a medication used to treat lepra reactions.

**Clinical Pearl / High-Yield Fact**
In patients with lepra reactions, the addition of a corticosteroid-sparing agent like ketotifen can help reduce the dose and duration of corticosteroid therapy, minimizing side effects and improving patient outcomes.

**Correct Answer:** C. Ketotifen.