Diagnosis: Fixed drug eruption
A fixed drug eruption is an adverse drug reaction manifested by skin lesions occurring at the same body site each time an individual is re-exposed to the specific drug. It is most frequently a solitary lesion but may sometimes be multiple. Lesions are usually asymptomatic but may cause burning or pruritus. Sometimes these lesions will form blisters. Post-inflammatory hyperpigmentation is common.
While more than 100 drugs have been implicated in causing fixed drug eruption, commonly associated drugs include trimethoprim-sulfamethoxazole (and other sulfonamides), naproxen, ibuprofen, tetracyclines, other antibiotics (ampicillin, metronidazole), barbiturates, oral contraceptives, quinine, and phenolphthalein. Lesions resolve when the offending medication is discontinued.