**Core Concept:** Fixed drug eruption (FDE) is a cutaneous adverse reaction to medications characterized by a recurrent, painful, and circumscribed maculopapular eruption at the same site after repeated exposure to the causative drug.

**Why the Correct Answer is Right:**

Fixed drug eruption is caused by a drug-induced hypersensitivity reaction mediated by the release of histamine and other mediators from mast cells and basophils. The repeated drug exposure leads to the accumulation of inflammatory cells and tissue damage, resulting in a characteristic pattern.

**Why Each Wrong Option is Incorrect:**

A. **Option A:** The correct answer does not mention hypersensitivity and tissue damage, which are key features of FDE.
B. **Option B:** Although some drugs can cause hypersensitivity reactions, the correct answer focuses on the specific mechanism and clinical features of FDE.
C. **Option C:** FDE is not caused by an immunodeficiency, but by a drug-induced immune response.
D. **Option D:** While some drugs can cause drug eruptions, the correct answer specifically relates to the pathogenesis and clinical presentation of FDE.

**Clinical Pearl:**

Fixed drug eruptions are often seen in patients with a history of recurrent exposure to the same drug. Common offending drugs include sulfonamides, NSAIDs, and antimalarials. Early recognition and discontinuation of the causative drug are crucial to prevent severe reactions and recurrence.

**Correct Answer:** D. Fixed drug eruption is a cutaneous adverse reaction triggered by the release of histamine and other inflammatory mediators during repeated exposure to the offending drug. This results in a characteristic pattern of a recurrent, painful maculopapular eruption at the same site following repeated drug intake.