**Core Concept**
Fixed drug eruption (FDE) is a type of adverse drug reaction characterized by the development of skin lesions or ulcers at the site of drug application, which recur upon re-exposure to the offending medication. This condition is often associated with sulfonamide antibiotics, among other drugs.

**Why the Correct Answer is Right**
In this scenario, the patient's recurrent ulcers on the glans, which heal with hyperpigmentation and recur after sulfonamide intake, are indicative of a fixed drug eruption. Sulfonamides can trigger FDE, leading to the development of characteristic skin lesions. This reaction is thought to occur due to the accumulation of reactive metabolites of the drug, which bind to skin cells and induce an immune response.

**Why Each Wrong Option is Incorrect**
**Option A:** Aphthous ulcers are typically painful, shallow ulcers that occur within the oral cavity, not on the glans. They are not associated with drug intake or hyperpigmentation.
**Option C:** Herpes genitalis is a viral infection caused by the herpes simplex virus, characterized by painful vesicles or ulcers on the genital area. It is not related to drug intake or fixed eruptions.
**Option D:** Chlamydial infection can cause urethritis, cervicitis, or lymphogranuloma venereum, but it does not typically present with recurrent ulcers or hyperpigmentation.

**Clinical Pearl / High-Yield Fact**
Fixed drug eruptions can involve various sites, including the skin, mucous membranes, and even the tongue. Re-exposure to the offending drug can trigger recurrence of the lesions, making it essential to avoid future exposure to the causative agent.

**✓ Correct Answer: B. fixed drug eruption**