Acute psychosis associated with oral trimethoprim-sulfamethoxazole therapy.

A 74 year old woman became progressively confused and developed visual hallucinations and delusions over a six day period, after the institution of routine oral trimethoprim-sulfamethoxazole therapy for a urinary tract infection. The medication was discontinued, and a marked improvement was noted 36 hours later. There was a complete return to normal mental functioning 60 hours after therapy was discontinued. The relationship between the patient's symptoms with the initiation and discontinuation of the medication suggests that the drug had a causal effect.