Neuropsychiatric Adverse Effects of Trimethoprim-Sulfamethoxazole: A Rare Case of Acute Psychosis in an Immunocompetent Patient

Trimethoprim-sulfamethoxazole (TMP-SMX) is a combination of two antibiotics used to treat various bacterial infections, generally well-tolerated but can rarely cause neuropsychological adverse effects, including psychosis. This case report describes a 69-year-old immunocompetent female who developed acute visual and auditory hallucinations three days after starting TMP-SMX for a urinary tract infection (UTI). The patient had a history of depression, successfully treated with mirtazapine a decade ago, and no other psychiatric or medical conditions. Laboratory tests and imaging were unremarkable. Symptoms resolved completely within two days of discontinuing TMP-SMX, suggesting a causal relationship. This case highlights the need for vigilance regarding the neuropsychiatric side effects of TMP-SMX, even in immunocompetent individuals, and underscores the importance of considering medication-induced psychosis in differential diagnoses. Further research is warranted to elucidate the mechanisms underlying this adverse drug reaction.