Acute Renal Failure Following Combined Treatment in Patient with Acute Retinal Necrosis and False-Positive Toxoplasmosis

Purpose: We report a case of acute renal failure following the use of a combination of high-dose oral valacyclovir and trimethoprim/ sulfamethoxazole in a patient with extensive retinal necrosis.Case summary: An 85-year-old woman came to our hospital with complaints of visual disturbance in her right eye. She was diagnosed with acute retinal necrosis and started on oral valacyclovir 1 g twice daily. Samples of aqueous humor and blood were collected to test for varicella-zoster virus DNA (via PCR) and the presence of uveitis (via laboratory tests). On day 7, her renal function remained stable but she tested positive for varicella-zoster virus as well as Toxoplasma IgM antibodies. Given the suspicion of atypical toxoplasmosis, she was treated with trimethoprim 80 mg/sulfamethoxazole 400 mg twice daily, clindamycin 300 mg four times daily, and prednisolone 30 mg. Three days later, she exhibited a decline in mental status and was admitted to the nephrology department with acute renal failure.Conclusions: When treating acute retinal necrosis, special attention to the possibility of renal failure is required for high-risk patients such as the elderly and those with low body weight. In particular, when Toxoplasma IgM antibodies are detected, reevaluation for false positives is crucial. Renal-sparing options such as intravitreal injections should be prioritized, as the combined use of systemic medications may increase the risk of renal failure.