Letermovir and Tacrolimus Drug–Drug Interaction in a Pediatric Kidney Transplant Patient: A Case Report and Review of the Literature

Background Cytomegalovirus (CMV) viremia is one of the most common opportunistic infections following solid organ transplant (SOT) in pediatric patients and can be associated with significant morbidity. Valganciclovir is the preferred antiviral medication used for CMV prophylaxis in high‐risk kidney transplant recipients, but its use is limited by myelosuppression. Letermovir is an alternative antiviral medication with lower rates of neutropenia. Letermovir has been implicated in many potential drug–drug interactions, including in combination with tacrolimus. Methods This report describes the case of a 6‐year‐old girl, 2 months post‐kidney transplant, at risk for CMV, who received letermovir for CMV prophylaxis after developing neutropenia while receiving valganciclovir. Her maintenance immunosuppression included tacrolimus. This report describes the drug–drug interaction of letermovir and tacrolimus, the dose adjustments required, and summarizes the available literature on the interaction. Results While on concurrent letermovir and tacrolimus, the patient required a 36% tacrolimus dose reduction and additional therapeutic drug level monitoring. Conclusion This case adds to the current limited data on the interaction of letermovir and tacrolimus in the pediatric SOT population.