Letermovir for Secondary Cytomegalovirus (CMV) Prophylaxis in a Pediatric Stem Cell Transplant Patient

Patients who undergo stem cell transplants are at a significant risk of infections. Cytomegalovirus (CMV) is an organism of particular concern in this population. Current treatments options for CMV include ganciclovir, valganciclovir, foscarnet, and cidofovir. These treatment options have adverse effects such as myelosuppression or nephrotoxicity, making them less than ideal as a treatment options. Increasing rates of drug resistance is another concern. The need for alternative treatment options is paramount. Many patients require secondary prophylaxis. Letermovir is a newly approved CMV DNA terminase complex inhibitor indicated for prophylaxis of CMV infection and disease in adults. Its role in secondary prophylaxis has not been clearly defined. We report the case of an 11-year old male who had undergone a 4/6 HLA-matched cord blood transplant for Fanconi Anemia. The patient developed CMV viremia that later progressed to CMV colitis and pneumonitis. He was initially treated with ganciclovir then was found to have UL97 mutation. He was then switched to foscarnet for induction therapy, to which the patient showed a good response. The patient was subsequently transitioned to cidofovir for maintenance therapy where CMV viremia recurred. Foscarnet was re-initiated with good response then transitioned to cidofovir maintenance therapy. Unfortunately, CMV viral load began to increase prompting a change to high-dose ganciclovir. Due to concerns for myelosuppression with using high-dose ganciclovir he was switched back to foscarnet. While on foscarnet the patient had nephrotoxicity and electrolyte disturbances and the decision was made to re-initiate high-dose ganciclovir. When the patient's CMV viral load was undetectable the patient was transitioned to letermovir 480 mg daily with successful suppression of CMV viral load. Letermovir has been well tolerated and the patient has experienced no adverse effects associated with it. The patient has not required further therapy for CMV viremia since starting letermovir. Letermovir prophylaxis was stopped after four months of therapy. The patient's CMV viral load began to rise after stopping for one month with the peak at 381 copies/mL. After restarting letermovir the CMV viral load became undetectable and has remained so. Letermovir could be useful in secondary prophylaxis in pediatric patients with ganciclovir-resistant CMV who are at risk of recurrences. Further investigation is warranted for the use of letermovir in the pediatric population.