Letermovir

eMC §4.2 (PREVYMIS 240 mg concentrate for solution for infusion). Should be initiated by a physician experienced in the management of patients who have had an allogeneic haematopoietic stem cell transplant (HSCT) or a kidney transplant. The 480 mg once-daily dose applies to adult and paediatric patients weighing at least 30 kg who are HSCT recipients, and to adult and paediatric patients weighing at least 40 kg who are kidney transplant recipients. HSCT PROPHYLAXIS DURATION: start after HSCT - may be started on the day of transplant and no later than 28 days post-HSCT, before or after engraftment - and continue through 100 days post-HSCT; prolonged prophylaxis beyond 100 days may benefit some patients at high risk of late CMV reactivation; safety and efficacy beyond 200 days has not been studied. KIDNEY TRANSPLANT: start on the day of transplant and no later than 7 days post-transplant, and continue through 200 days post-transplant. CICLOSPORIN DOSE ADJUSTMENT: if co-administered with ciclosporin, decrease letermovir to 240 mg once daily; if ciclosporin is initiated after starting letermovir, decrease the next letermovir dose to 240 mg once daily; if ciclosporin is discontinued after starting letermovir, increase the next letermovir dose to 480 mg once daily; if ciclosporin dosing is temporarily interrupted because of high ciclosporin levels, no letermovir dose adjustment is needed. For paediatric patients weighing less than 30 kg receiving intravenous letermovir, the SPC states no adjustment is required for co-administered ciclosporin. MISSED DOSE: give as soon as possible; if it is time for the next dose, skip the missed dose and return to the regular schedule - do not double the next dose or give more than prescribed. ELDERLY: no dose adjustment based on age. HEPATIC IMPAIRMENT: no dose adjustment for mild (Child-Pugh A) to moderate (Child-Pugh B) impairment; not recommended in severe (Child-Pugh C) impairment; not recommended in moderate hepatic impairment combined with moderate or severe renal impairment. ADMINISTRATION: if possible, intravenous administration should not exceed 4 weeks. The diluted solution must be administered through a sterile 0.2 or 0.22 micron PES in-line filter and no other filter; the entire contents of the intravenous bag should be administered. PAEDIATRIC: the SPC gives fixed once-daily intravenous doses for HSCT recipients weighing less than 30 kg in weight bands (SPC Table 1) - obtain those bands from the SPC and a children's formulary rather than extrapolating; dose adjustment may be necessary for paediatric patients weighing less than 30 kg when switching between oral and intravenous formulations. Safety and efficacy have not been established in HSCT patients weighing less than 5 kg or in kidney transplant patients weighing less than 40 kg, and no posology recommendation can be supported for kidney transplant patients weighing less than 40 kg. US labelling (PREVYMIS, Merck Sharp & Dohme, label date 2026-01-14) agrees on 480 mg once daily orally or as an intravenous infusion over 1 hour, reduced to 240 mg once daily with cyclosporine, and states the injection should be used only in patients unable to take oral therapy, switching to oral as soon as able.