A 50-year-old woman develops pink macules and papules on her hands and forearms in association with a sore throat. The lesions are targetlike, with the centers a dusky violet. A diagnosis of erythema multiforme is made. The most important information obtained from this patient's history is

(b) Source: (Braunwald, 15/e, pp 337-339.) Erythema multiforme is often caused by drugs. It is most important to identify the offending agent. Phenytoin can induce erythema multiforme, so this information is critical. Sulfa drugs, barbiturates, and penicillin can also be causes. The rash, with its target lesions, should not be confused with toxic shock or measles. The sore throat is likely to be a symptom from the process itself, suggesting involvement of the oral mucosa.