Compassionate Use of Maribavir for Treatment of Resistant CMV Infection in a Pediatric Patient Undergoing BMT

Cytomegalovirus (CMV) infection is one of the main infectious complications in patients undergoing hematopoietic stem cell transplant (BMT), and is associated with significant morbidity and mortality. Conventional treatment with antivirals such as ganciclovir, foscarnet, and cidofovir is often limited by hematologic toxicity or nephrotoxicity. Maribavir, an inhibitor of CMV UL97 protein kinase, was approved by the Brazilian National Committee for Health Technology Incorporation (CONITEC) in December 2024 for refractory or resistant CMV infections in transplant patients older than 12 years. However, there are no guidelines for its use in pediatric patients. A 5-year-old girl underwent unrelated allogeneic BMT on 03/10/2024 for severe immunodeficiency secondary to Chediak–Higashi syndrome. Conditioning included busulfan, fludarabine, and alemtuzumab, with post-transplant immunosuppression based on cyclosporine and mycophenolate. On 15/10/2024, she presented CMV reactivation (2,362 IU, log 3.37), and preemptive treatment with ganciclovir was started. After 14 days, viremia increased to 11,595 IU (log 4.06), characterizing refractoriness. Despite therapeutic adjustments, viral load continued to rise, reaching 604,144 IU (log 5.46) on 10/02/2025. Genotyping detected the C603W mutation, conferring resistance to ganciclovir. Given disease progression, maribavir was started on 12/03/2025. Progressive decline in viremia was observed, with negativity achieved on 15/05/2025. During treatment, renal and hepatic function and blood counts remained stable. The only reported adverse effect was decreased appetite, likely due to dysgeusia. The patient was discharged in good general condition and remains under outpatient follow-up, without viral reactivation. This case represents a positive experience with maribavir use in a pediatric patient with resistant CMV infection, demonstrating virologic efficacy and good safety profile. It underscores the importance of additional clinical studies to validate maribavir use in pediatric transplant populations.