Pharmacokinetics, Safety, and Efficacy of Letermovir for Cytomegalovirus Prophylaxis in Adolescent Hematopoietic Cell Transplantation Recipients.

INTRODUCTION: Letermovir is a cytomegalovirus (CMV) terminase complex inhibitor approved for prophylaxis of CMV infection and disease in adult CMV-seropositive allogeneic hematopoietic cell transplantation (allo-HCT) recipients (R+). We report pharmacokinetics (PK), safety, and efficacy of letermovir in adolescent (12-18 years) allogeneic HCT recipients from an ongoing clinical study. METHODS: In this phase 2b, multicenter, open-label study (NCT03940586), 28 adolescents received 480 mg letermovir [240 mg with cyclosporin A (CsA)] once daily orally or intravenously. Blood was collected for intensive (n = 14) plasma concentrations of letermovir. Intensive PK data were used for dose confirmation. Target exposure range 34,400-100,000 h × ng/mL for pediatric median exposures was based on model-predicted phase 3 population PK simulations in adult HCT recipients. RESULTS: All participants were CMV-seropositive (body weight 28.7-95.0 kg). Of 12 PK-evaluable participants, 8 receiving 480 mg letermovir without CsA and 4 receiving 240 mg letermovir with CsA achieved exposures comparable to the adult exposure range. Exposure above the target but below the adult clinical program maximum was observed in 1 patient. Safety was consistent with previously described safety in adults. The proportion of participants with clinically significant CMV infection through week 24 post-HCT was comparable (24%) to that in the pivotal phase 3 study in adults (37.5%). CONCLUSIONS: Administration of adult letermovir doses in this adolescent cohort resulted in exposures within adult clinical program margins and was associated with safety and efficacy similar to adults. Results support a letermovir dose of 480 mg (240 mg with CsA) in adolescent allo-HCT recipients.

Efficacy and safety of extended duration letermovir prophylaxis in recipients of haematopoietic stem-cell transplantation at risk of cytomegalovirus infection: a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial.

BACKGROUND: In a pivotal phase 3 trial of cytomegalovirus prophylaxis with letermovir for up to 100 days after allogeneic haematopoietic stem-cell transplantation (HSCT), 12% of participants developed clinically significant cytomegalovirus infection after letermovir was discontinued. We aimed to evaluate the efficacy and safety of extending the duration of letermovir prophylaxis for clinically significant cytomegalovirus infection from 100 days to 200 days following HSCT. METHODS: We conducted a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial at 32 sites in six countries (France, Germany, Italy, Japan, the UK, and the USA). Cytomegalovirus­seropositive HSCT recipients (aged ≥18 years) who had received letermovir prophylaxis for up to 100 days following HSCT and who remained at high risk of late clinically significant cytomegalovirus infection (with no previous history of clinically significant cytomegalovirus infection, defined as initiation of pre-emptive therapy for documented cytomegalovirus viraemia, onset of cytomegalovirus end-organ disease, or both) were eligible. Participants were randomly assigned (2:1) to receive either an additional 100 days (ie, a total of 200 days; letermovir group) of oral or intravenous letermovir 480 mg once daily, adjusted to 240 mg once daily for participants on cyclosporin A, or 100 days of a placebo comparator for letermovir (ie, a total of 100 days of letermovir; placebo group), following HSCT. Randomisation was done using a central interactive response technology system, stratified by study centre and haploidentical donor (yes or no). Participants, investigators, and sponsor personnel were masked to the treatment allocation. The primary efficacy endpoint was the proportion of participants from randomisation to week 28 (200 days after HSCT) with clinically significant cytomegalovirus infection, analysed using the full analysis set population (ie, those who received at least one dose of study intervention). Safety was analysed in all participants as treated (ie, those who received at least one dose according to the study intervention they were assigned to). This study is registered with ClinicalTrials.gov, NCT03930615, and is complete. FINDINGS: Between June 21, 2019, and March 16, 2022, 255 patients were screened for eligibility and 220 (86%) were randomly assigned (145 [66%] in the letermovir group and 75 [34%] in the placebo group). Between randomisation and week 28, four (3%) of 144 participants in the letermovir group and 14 (19%) of 74 in the placebo group developed clinically significant cytomegalovirus infection (treatment difference -16·1% [95% CI -25·8 to -6·5]; p=0·0005). The most common adverse events among participants in the letermovir group versus the placebo group were graft-versus-host disease (43 [30%] vs 23 [31%]), diarrhoea (17 [12%] vs nine [12%]), nausea (16 [11%] vs 13 [18%]), pyrexia (13 [9%] vs nine [12%]), and decreased appetite (six [4%] vs nine [12%]). The most frequently reported serious adverse events were recurrent acute myeloid leukaemia (six [4%] vs none) and pneumonia (three [2%] vs two [3%]). No deaths were considered to be drug-related by the investigator. INTERPRETATION: Extending the duration of letermovir prophylaxis to 200 days following HSCT is efficacious and safe in reducing the incidence of late clinically significant cytomegalovirus infection in patients at risk. FUNDING: Merck Sharp & Dohme LLC.

Letermovir vs Valganciclovir for Prophylaxis of Cytomegalovirus in High-Risk Kidney Transplant Recipients: A Randomized Clinical Trial.

Importance: Valganciclovir for 200 days is standard care for cytomegalovirus (CMV) prophylaxis in high-risk CMV-seronegative kidney transplant recipients who receive an organ from a CMV-seropositive donor, but its use is limited by myelosuppression. Objective: To compare the efficacy and safety of letermovir with valganciclovir for prevention of CMV disease in CMV-seronegative kidney transplant recipients who receive an organ from a CMV-seropositive donor. Design, Setting, and Participants: Randomized, double-masked, double-dummy, noninferiority, phase 3 trial in adult CMV-seronegative kidney transplant recipients who received an organ from a CMV-seropositive donor at 94 participating sites between May 2018 and April 2021 (final follow-up in April 2022). Interventions: Participants were randomized in a 1:1 ratio (stratified by receipt of lymphocyte-depleting induction immunosuppression) to receive letermovir, 480 mg, orally daily (with acyclovir) or valganciclovir, 900 mg, orally daily (adjusted for kidney function) for up to 200 days after transplant, with matching placebos. Main Outcomes and Measures: The primary outcome was CMV disease, confirmed by an independent masked adjudication committee, through posttransplant week 52 (prespecified noninferiority margin, 10%). CMV disease through week 28 and time to onset of CMV disease through week 52 were secondary outcomes. Exploratory outcomes included quantifiable CMV DNAemia and resistance. The rate of leukopenia or neutropenia through week 28 was a prespecified safety outcome. Results: Among 601 participants randomized, 589 received at least 1 dose of the study drug (mean age, 49.6 years; 422 [71.6%] men). Letermovir (n = 289) was noninferior to valganciclovir (n = 297) for prevention of CMV disease through week 52 (10.4% vs 11.8% of participants with committee-confirmed CMV disease; stratum-adjusted difference -1.4% [95% CI, -6.5% to 3.8%]). No participants who received letermovir vs 5 participants (1.7%) who received valganciclovir developed CMV disease through week 28. Time to onset of CMV disease was comparable between the groups (hazard ratio, 0.90 [95% CI, 0.56-1.47]). Quantifiable CMV DNAemia was detected in 2.1% of participants in the letermovir group vs 8.8% in the valganciclovir group by week 28. Of participants evaluated for suspected CMV disease or CMV DNAemia, none (0/52) who received letermovir and 12.1% (8/66) who received valganciclovir had resistance-associated substitutions. The rate of leukopenia or neutropenia through week 28 was lower with letermovir vs valganciclovir (26% vs 64%; difference, -37.9% [95% CI, -45.1% to -30.3%]; P < .001). Fewer participants in the letermovir group than the valganciclovir group discontinued prophylaxis due to adverse events (4.1% vs 13.5%) or drug-related adverse events (2.7% vs 8.8%). Conclusion and Relevance: Among adult CMV-seronegative kidney transplant recipients who received an organ from a CMV-seropositive donor, letermovir was noninferior to valganciclovir for prophylaxis of CMV disease over 52 weeks, with lower rates of leukopenia or neutropenia, supporting its use for this indication. Trial Registration: ClinicalTrials.gov Identifier: NCT03443869; EudraCT: 2017-001055-30.

A Mortality Analysis of Letermovir Prophylaxis for Cytomegalovirus (CMV) in CMV-seropositive Recipients of Allogeneic Hematopoietic Cell Transplantation.

BACKGROUND: In a phase 3 trial, letermovir reduced clinically significant cytomegalovirus infections (CS-CMVi) and all-cause mortality at week 24 versus placebo in CMV-seropositive allogeneic hematopoietic cell transplantation (HCT) recipients. This post hoc analysis of phase 3 data further investigated the effects of letermovir on all-cause mortality. METHODS: Kaplan-Meier survival curves were generated by treatment group for all-cause mortality. Observations were censored at trial discontinuation for reasons other than death or at trial completion. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated using Cox modeling, adjusting for risk factors associated with mortality. RESULTS: Of 495 patients with no detectable CMV DNA at randomization, 437 had vital-status data available through week 48 post-HCT at trial completion (101 deaths, 20.4%). Following letermovir prophylaxis, the HR for all-cause mortality was 0.58 (95% CI, 0.35-0.98; P = .04) at week 24 and 0.74 (95% CI, 0.49-1.11; P = .14) at week 48 post-HCT versus placebo. Incidence of all-cause mortality through week 48 post-HCT in the letermovir group was similar in patients with or without CS-CMVi (15.8 vs 19.4%; P = .71). However, in the placebo group, all-cause mortality at week 48 post-HCT was higher in patients with versus those without CS-CMVi (31.0% vs 18.2%; P = .02). The HR for all-cause mortality in patients with CS-CMVi was 0.45 (95% CI, 0.21-1.00; P = .05) at week 48 for letermovir versus placebo. CONCLUSIONS: Letermovir may reduce mortality by preventing or delaying CS-CMVi in HCT recipients. CLINICAL TRIALS REGISTRATION: clinicaltrials.gov, NCT02137772.

Outcomes of patients with detectable CMV DNA at randomization in the phase III trial of letermovir for the prevention of CMV infection in allogeneic hematopoietic cell transplantation.

Letermovir, a cytomegalovirus (CMV) terminase-complex inhibitor, is indicated for prophylaxis of CMV infection and disease in adult CMV-seropositive recipients of allogeneic hematopoietic cell transplantation (HCT). In a phase III, double-blind, randomized trial, letermovir significantly reduced the risk of clinically significant CMV infection (CS-CMVi) vs placebo through Week 24 post-HCT. This analysis investigated outcomes in participants with detectable CMV DNA at randomization, who were excluded from the primary efficacy analysis. In total, 70 of 565 randomized participants had detectable CMV DNA at randomization (letermovir 48; placebo 22). Study treatment completion rates were greater in letermovir-treated participants compared with placebo (52.1% vs 9.1%). The incidence of CS-CMVi or imputed primary endpoint events through Week 24 were 64.6% and 90.9% in the letermovir and placebo groups, respectively (treatment difference -26.1%; P = .010). Kaplan-Meier event rates for CS-CMVi onset through Week 14 (end-of-treatment period) were 33.1% for letermovir and 86.6% for placebo (P < .001). Median viral loads at the CS-CMVi events was similar in both treatment arms. All-cause mortality through Week 24 posttransplant was 15.0% for letermovir and 18.2% for placebo; through Week 48, mortality rates were 26.5% and 40.9%, respectively (P = .268). Overall, clinical outcomes were similar to those reported for participants with undetectable CMV DNA at randomization.

Letermovir Prophylaxis for Cytomegalovirus in Hematopoietic-Cell Transplantation.

BACKGROUND: Cytomegalovirus (CMV) infection remains a common complication after allogeneic hematopoietic-cell transplantation. Letermovir is an antiviral drug that inhibits the CMV-terminase complex. METHODS: In this phase 3, double-blind trial, we randomly assigned CMV-seropositive transplant recipients, 18 years of age or older, in a 2:1 ratio to receive letermovir or placebo, administered orally or intravenously, through week 14 after transplantation; randomization was stratified according to trial site and CMV disease risk. Letermovir was administered at a dose of 480 mg per day (or 240 mg per day in patients taking cyclosporine). Patients in whom clinically significant CMV infection (CMV disease or CMV viremia leading to preemptive treatment) developed discontinued the trial regimen and received anti-CMV treatment. The primary end point was the proportion of patients, among patients without detectable CMV DNA at randomization, who had clinically significant CMV infection through week 24 after transplantation. Patients who discontinued the trial or had missing end-point data at week 24 were imputed as having a primary end-point event. Patients were followed through week 48 after transplantation. RESULTS: From June 2014 to March 2016, a total of 565 patients underwent randomization and received letermovir or placebo beginning a median of 9 days after transplantation. Among 495 patients with undetectable CMV DNA at randomization, fewer patients in the letermovir group than in the placebo group had clinically significant CMV infection or were imputed as having a primary end-point event by week 24 after transplantation (122 of 325 patients [37.5%] vs. 103 of 170 [60.6%], P<0.001). The frequency and severity of adverse events were similar in the two groups overall. Vomiting was reported in 18.5% of the patients who received letermovir and in 13.5% of those who received placebo; edema in 14.5% and 9.4%, respectively; and atrial fibrillation or flutter in 4.6% and 1.0%, respectively. The rates of myelotoxic and nephrotoxic events were similar in the letermovir group and the placebo group. All-cause mortality at week 48 after transplantation was 20.9% among letermovir recipients and 25.5% among placebo recipients. CONCLUSIONS: Letermovir prophylaxis resulted in a significantly lower risk of clinically significant CMV infection than placebo. Adverse events with letermovir were mainly of low grade. (Funded by Merck; ClinicalTrials.gov number, NCT02137772 ; EudraCT number, 2013-003831-31 .).