Fixed Drug Eruption on the Penis Due to Trimethoprim-Sulfamethoxazole: A Case Report

A fixed drug eruption (FDE) is a common dermatological drug side effect but can go unnoticed. It is characterized by an oval-circular erythematous patch, sometimes with itching and burning pain localized in many parts of the body, such as the face, lips, torso, limbs, and anogenital area. Its diagnosis is generally clinical, but it can be mistaken for other dermatological diseases seen in primary care, like balanitis, genital herpes, and lichen planus. It can be a diagnostic challenge for primary care physicians when it is not considered. We present a 26-year-old man who developed an FDE in the penis with intense itching and burning pain during his labor hours after 15 minutes of consuming an oral dose of trimethoprim-sulfamethoxazole for a gastrointestinal infection. The patient was treated with topical corticosteroids twice per day and educated to avoid the use of the antibiotic again. In the next few days, the symptoms fully resolved, and he developed post-inflammatory hyperpigmentation in the area. The primary management of an FDE is immediate discontinuation of the offending drug and use of topical corticosteroids to prevent possible generalized reactions and recurrence of lesions. Therefore, the primary care physician should consider this condition in his or her diagnosis when new dermatologic lesions occur after exposure to a new drug.