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A 17yo boy presents with a round lesion similar to that noted below, but on his penis, noted 1 hour after taking a dose of TMP-SMX that was prescribed to him for “stomach infection.” He had 2 episodes of non-bloody diarrhea 2 days ago and went to a clinic and received the prescription, which he was unable to fill until today. The diarrhea has actually improved. He has no fever. The rash is not painful or itchy. He mentions that he previously had a similar rash in the same place after taking the same drug a few years ago.

Fixed drug eruptionWikimedia Commons Donald M. Pillsbury, M.D., and Clarence S. Livingood

What is your best course of action?