Maribavir for Refractory or Resistant Cytomegalovirus Infections in Hematopoietic-cell or Solid-organ Transplant Recipients: A Randomized, Dose-ranging, Double-blind, Phase 2 Study

Effect of Food, Crushing of Tablets, and Antacid Coadministration on Maribavir Pharmacokinetics in Healthy Adult Participants: Results From 2 Phase 1, Open-Label, Randomized, Crossover Studies

The effect of food composition, tablet crushing, and antacid coadministration on maribavir pharmacokinetics was assessed in 2 Phase 1 studies in healthy adults. In the first, a single maribavir 400-mg dose was administered under fasting conditions, with a low-fat/low-calorie or a high-fat/high-calorie meal. In the second, a single maribavir 100-mg dose was administered under fasting conditions, as a crushed tablet, or as a whole tablet alone or with an antacid. The 90% confidence intervals of the geometric mean ratios were within 80%-125% for area under the concentration-time curve (AUC), but not for maximum plasma concentration (Cmax) for low-fat/low-calorie and high-fat/high-calorie meals versus fasting or for whole tablet with antacid versus whole tablet alone. The 90% confidence intervals of the geometric mean ratios for AUC and Cmax were within 80%-125% for crushed versus whole tablet. Maribavir median time to Cmax value in plasma under fed conditions was delayed versus fasting conditions, but there was no statistical difference for crushed versus whole tablet or with versus without antacid. As the antiviral efficacy of maribavir is driven by AUC but not Cmax, findings suggest that maribavir can be administered with food or antacids or as a crushed tablet.

Antiviral medications for preventing cytomegalovirus disease in solid organ transplant recipients

BACKGROUND

The risk of cytomegalovirus (CMV) infection in solid organ transplant recipients has resulted in the frequent use of prophylaxis to prevent the clinical syndrome associated with CMV infection. This is an update of a review first published in 2005 and updated in 2008 and 2013.

OBJECTIVES

To determine the benefits and harms of antiviral medications to prevent CMV disease and all-cause death in solid organ transplant recipients.

SEARCH METHODS

We contacted the information specialist and searched the Cochrane Kidney and Transplant Register of Studies up to 5 February 2024 using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Registry Platform (ICTRP) Search Portal, and ClinicalTrials.gov.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) and quasi-RCTs comparing antiviral medications with placebo or no treatment, comparing different antiviral medications or different regimens of the same antiviral medications for CMV prophylaxis in recipients of any solid organ transplant. Studies examining pre-emptive therapy for CMV infection are studied in a separate review and were excluded from this review.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed study eligibility, risk of bias and extracted data. Summary estimates of effect were obtained using a random-effects model, and results were expressed as risk ratios (RR) and their 95% confidence intervals (CI) for dichotomous outcomes and mean difference (MD) and 95% CI for continuous outcomes. Confidence in the evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.

MAIN RESULTS

This 2024 update found four new studies, bringing the total number of included studies to 41 (5054 participants). The risk of bias was high or unclear across most studies, with a low risk of bias for sequence generation (12), allocation concealment (12), blinding (11) and selective outcome reporting (9) in fewer studies. There is high-certainty evidence that prophylaxis with aciclovir, ganciclovir or valaciclovir compared with placebo or no treatment is more effective in preventing CMV disease (19 studies: RR 0.42, 95% CI 0.34 to 0.52), all-cause death (17 studies: RR 0.63, 95% CI 0.43 to 0.92), and CMV infection (17 studies: RR 0.61, 95% CI 0.48 to 0.77). There is moderate-certainty evidence that prophylaxis probably reduces death from CMV disease (7 studies: RR 0.26, 95% CI 0.08 to 0.78). Prophylaxis reduces the risk of herpes simplex and herpes zoster disease, bacterial and protozoal infections but probably makes little to no difference to fungal infection, acute rejection or graft loss. No apparent differences in adverse events with aciclovir, ganciclovir or valaciclovir compared with placebo or no treatment were found. There is high certainty evidence that ganciclovir, when compared with aciclovir, is more effective in preventing CMV disease (7 studies: RR 0.37, 95% CI 0.23 to 0.60). There may be little to no difference in any outcome between valganciclovir and IV ganciclovir compared with oral ganciclovir (low certainty evidence). The efficacy and adverse effects of valganciclovir or ganciclovir were probably no different to valaciclovir in three studies (moderate certainty evidence). There is moderate certainty evidence that extended duration prophylaxis probably reduces the risk of CMV disease compared with three months of therapy (2 studies: RR 0.20, 95% CI 0.12 to 0.35), with probably little to no difference in rates of adverse events. Low certainty evidence suggests that 450 mg/day valganciclovir compared with 900 mg/day valganciclovir results in little to no difference in all-cause death, CMV infection, acute rejection, and graft loss (no information on adverse events). Maribavir may increase CMV infection compared with ganciclovir (1 study: RR 1.34, 95% CI: 1.10 to 1.65; moderate certainty evidence); however, little to no difference between the two treatments were found for CMV disease, all-cause death, acute rejection, and adverse events at six months (low certainty evidence).

AUTHORS' CONCLUSIONS

Prophylaxis with antiviral medications reduces CMV disease and CMV-associated death, compared with placebo or no treatment, in solid organ transplant recipients. These data support the continued routine use of antiviral prophylaxis in CMV-positive recipients and CMV-negative recipients of CMV-positive organ transplants.

Physiologically Based Pharmacokinetic Modeling for Maribavir to Inform Dosing in Drug-Drug Interaction Scenarios with CYP3A4 Inducers and Inhibitors

Maribavir, an orally available antiviral agent, has been approved in multiple countries for the treatment of patients with refractory post-transplant cytomegalovirus (CMV) infection and/or disease. Maribavir is primarily metabolized by CYP3A4; coadministration with CYP3A4 inducers and inhibitors may significantly alter maribavir exposure, thereby affecting its efficacy and safety. The effect of CYP3A4 inducers and inhibitors on maribavir exposure was evaluated based on a drug-drug interaction (DDI) study and physiologically-based pharmacokinetic (PBPK) modeling. The effect of rifampin (a strong inducer of CYP3A4 and moderate inducer of CYP1A2), administered at a 600 mg dose once daily, on maribavir pharmacokinetics was assessed in a clinical phase 1 DDI study in healthy participants. A full PBPK model for maribavir was developed and verified using in vitro and clinical pharmacokinetic data from phase 1 studies. The verified PBPK model was then used to simulate maribavir DDI interactions with various CYP3A4 inducers and inhibitors. The DDI study results showed that coadministration with rifampin decreased the maribavir maximum plasma concentration (Cmax), area under the plasma concentration-time curve (AUC), and trough concentration (Ctrough) by 39%, 60%, and 82%, respectively. Based on the results from the clinical DDI study, the coadministration of maribavir with rifampin is not recommended. The PBPK model did not predict a clinically significant effect of CYP3A4 inhibitors on maribavir exposure; however, it predicted that strong or moderate CYP3A4 inducers, including carbamazepine, efavirenz, phenobarbital, and phenytoin, may reduce maribavir exposure to a clinically significant extent, and may prompt the consideration of a maribavir dosing increase, in accordance with local approved labels and/or regulations.

Approaches and Challenges in the Current Management of Cytomegalovirus in Transplant Recipients: Highlighting the Role of Advanced Practice Providers (Nurse Practitioners and Physician Assistants)

Cytomegalovirus (CMV) infection is associated with increased morbidity and mortality in hematopoietic cell transplant (HCT) and solid organ transplant (SOT) recipients, with traditional anti-CMV therapies limited by their associated toxicities and the development of resistance. Clinical providers are often faced with challenging and complicated CMV infections that require multiple courses of antiviral therapies. Increasingly, advanced practice providers (APPs) are playing an important role in the day-to-day management of transplant recipients with CMV infection, including resistant/refractory CMV and other complex CMV syndromes. Here, we provide an overview of current preventative and treatment strategies for CMV infection in HCT and SOT recipients, highlighting the challenging aspects of current management and the potential utility of newer antiviral agents. This article also focuses on how a multidisciplinary team, orchestrated by APPs, can improve CMV-associated patient outcomes. Protocols using antiviral agents for the prevention or treatment of CMV infections require carefully designed and meticulously implemented strategies to ensure the best clinical outcomes for patients. APPs, who have increasingly become the frontline providers of outpatient care for transplant recipients, are ideally positioned to design and carry out these protocols.

Recent advances in cytomegalovirus infection management in solid organ transplant recipients

PURPOSE OF REVIEW

Human cytomegalovirus (CMV) continues to be the most important infectious complication following solid organ transplantation (SOT).

RECENT FINDINGS

Universal prophylaxis and preemptive therapy are the most adopted strategies for prevention of CMV disease globally. Prophylaxis with valganciclovir is the most widely used approach to CMV prevention, however leukopenia and late onset CMV disease after discontinuation of prophylaxis requires new strategies to prevent this complication. The use of assays detecting CMV-specific T cell-mediated immunity may individualize the duration of antiviral prophylaxis after transplantation. Letermovir has been recently approved for prophylaxis in kidney transplant recipients. CMV-RNAemia used together with CMV-DNAemia in the viral surveillance of CMV infection provides accurate information on viral load kinetics, mostly in patients receiving letermovir prophylaxis/therapy. The development of refractory and resistant CMV infection remains a major challenge and a new treatment with maribavir is currently available. In the present paper we will review the most recent advances in prevention and treatment of CMV diseases in SOT recipients.

SUMMARY

Recent findings, summarized in the present paper, may be useful to optimize prevention and treatment of CMV infection in SOT.

What's New: Updates on Cytomegalovirus in Solid Organ Transplantation

Cytomegalovirus (CMV) is one of the most common infections occurring after solid organ transplantation. This high burden of disease, which incurs sizeable morbidity, may be worsening with the proportion of high-risk D+/R- solid organ transplantation recipients increasing in some regions globally. Cohort studies continue to support either universal prophylaxis or preemptive therapy as effective prevention strategies. Letermovir prophylaxis was noninferior to valganciclovir in adult high-risk D+/R- kidney transplant recipients with fewer drug-related adverse events in a recent clinical trial and has now been approved for such use in some regions. Maribavir preemptive therapy failed to demonstrate noninferiority when compared with valganciclovir in hematopoietic stem cell transplant recipients but looked promising for safety. Donor matching could be useful in prevention CMV disease with a survival advantage demonstrated in seronegative recipients waiting up to 30 mo for a seronegative kidney. Immune-guided prophylaxis resulted in fewer CMV infection episodes in lung transplant recipients when compared with fixed-duration prophylaxis in a recent clinical trial. For treatment of refractory or resistant CMV infection, maribavir was more efficacious and better tolerated when compared with investigator-initiated therapy in its registration trial for this condition. Further research regarding best treatment and prophylaxis of resistant or refractory CMV infection is needed to reflect best clinical practice choices. Optimal use of immune globulin or CMV-specific T cells for prevention or treatment of CMV disease remains undefined. Standardized definitions for the design of CMV clinical trials have been developed. In this review, we highlight recent updates in the field from data published since 2018.

Use of Maribavir for Multidrug Resistant Cytomegaloviremia in a Pediatric Oncology Patient

Resistant and refractory cytomegalovirus (CMV) viremia can limit the provision of chemotherapy due to myelosuppression and end-organ dysfunction. Few therapies are available for children with clinically significant CMV viremia. We successfully used maribavir for a 4-year-old patient with lymphoma to complete his chemotherapy course. Resistance to maribavir did result after many months of therapy.

Treatment for First Cytomegalovirus Infection Post-Hematopoietic Cell Transplant in the AURORA Trial: A Multicenter, Double-Blind, Randomized, Phase 3 Trial Comparing Maribavir With Valganciclovir

BACKGROUND

Neutropenia may limit the use of valganciclovir treatment for cytomegalovirus (CMV) infection following hematopoietic cell transplant (HCT). A phase 2 study indicated efficacy of maribavir with fewer treatment-limiting toxicities than valganciclovir.

METHODS

In this multicenter, double-blind, phase 3 study, patients with first asymptomatic CMV infection post-HCT were stratified and randomized 1:1 to maribavir 400 mg twice daily or valganciclovir (dose-adjusted for renal clearance) for 8 weeks with 12 weeks of follow-up. The primary endpoint was confirmed CMV viremia clearance at week 8 (primary hypothesis of noninferiority margin of 7.0%). The key secondary endpoint was a composite of the primary endpoint with no findings of CMV tissue-invasive disease at week 8 through week 16. Treatment-emergent adverse events (TEAEs) were assessed.

RESULTS

Among patients treated (273 maribavir; 274 valganciclovir), the primary endpoint of noninferiority of maribavir was not met (maribavir, 69.6%; valganciclovir, 77.4%; adjusted difference: -7.7%; 95% confidence interval [CI]: -14.98, -.36; lower limit of 95% CI of treatment difference exceeded -7.0%). At week 16, 52.7% and 48.5% of patients treated (maribavir and valganciclovir, respectively) maintained CMV viremia clearance without tissue-invasive disease (adjusted difference: 4.4%; 95% CI: -3.91, 12.76). With maribavir (vs valganciclovir), fewer patients experienced neutropenia (16.1% and 52.9%) or discontinued due to TEAEs (27.8% and 41.2%). Discontinuations were mostly due to neutropenia (maribavir, 4.0%; valganciclovir, 17.5%).

CONCLUSIONS

Although noninferiority of maribavir to valganciclovir for the primary endpoint was not achieved based on the prespecified noninferiority margin, maribavir demonstrated comparable CMV viremia clearance during post-treatment follow-up, with fewer discontinuations due to neutropenia. Clinical Trials Registration. NCT02927067 [AURORA].

Opportunistic Infections Post-Lung Transplantation: Viral, Fungal, and Mycobacterial

Opportunistic infections are a leading cause of lung transplant recipient morbidity and mortality. Risk factors for infection include continuous exposure of the lung allograft to the external environment, high levels of immunosuppression, impaired mucociliary clearance and decreased cough reflex, and impact of the native lung microbiome in single lung transplant recipients. Infection risk is mitigated through careful pretransplant screening of recipients and donors, implementation of antimicrobial prophylaxis strategies, and routine surveillance posttransplant. This review describes common viral, fungal, and mycobacterial infectious after lung transplant and provides recommendations on prevention and treatment.

Current and Emerging Antiviral Agents in the Prevention and Treatment of Cytomegalovirus in Pediatric Transplant Recipients

Despite current prophylaxis regimens, cytomegalovirus (CMV) is common in hematopoietic cell transplantation (HCT) and solid organ transplantation (SOT) and remains a significant cause of morbidity and mortality. Newer antiviral medications are reshaping the landscape for prevention and treatment of CMV DNAemia, infection, and disease. Letermovir is approved for CMV prevention in adult HCT patients and is attractive due to the absence of marrow suppression seen with ganciclovir/valganciclovir. Letermovir should not be routinely used for CMV treatment due to its low threshold for resistance. Maribavir is approved for the treatment of refractory or resistant CMV disease in HCT and SOT recipients ≥12 years of age, though it has no current role in CMV prevention. More research is needed to fully elucidate the roles, efficacy, and safety of these newer agents in prevention and treatment of CMV in pediatric transplant recipients.

Human Cytomegalovirus (HCMV) Genetic Diversity, Drug Resistance Testing and Prevalence of the Resistance Mutations: A Literature Review

Human cytomegalovirus (HCMV) is a pathogen with high prevalence in the general population that is responsible for high morbidity and mortality in immunocompromised individuals and newborns, while remaining mainly asymptomatic in healthy individuals. The HCMV genome is 236,000 nucleotides long and encodes approximately 200 genes in more than 170 open reading frames, with the highest rate of genetic polymorphisms occurring in the envelope glycoproteins. HCMV infection is treated with antiviral drugs such as ganciclovir, valganciclovir, cidofovir, foscarnet, letermovir and maribavir targeting viral enzymes, DNA polymerase, kinase and the terminase complex. One of the obstacles to successful therapy is the emergence of drug resistance, which can be tested phenotypically or by genotyping using Sanger sequencing, which is a widely available but less sensitive method, or next-generation sequencing performed in samples with a lower viral load to detect minority variants, those representing approximately 1% of the population. The prevalence of drug resistance depends on the population tested, as well as the drug, and ranges from no mutations detected to up to almost 50%. A high prevalence of resistance emphasizes the importance of testing the patient whenever resistance is suspected, which requires the development of more sensitive and rapid tests while also highlighting the need for alternative therapeutic targets, strategies and the development of an effective vaccine.

Drug Resistance Assessed in a Phase 3 Clinical Trial of Maribavir Therapy for Refractory or Resistant Cytomegalovirus Infection in Transplant Recipients

BACKGROUND

This drug resistance analysis of a randomized trial includes 234 patients receiving maribavir and 116 receiving investigator-assigned standard therapy (IAT), where 56% and 24%, respectively, cleared cytomegalovirus DNA at week 8 (treatment responders).

METHODS

Baseline and posttreatment plasma samples were tested for mutations conferring drug resistance in viral genes UL97, UL54, and UL27.

RESULTS

At baseline, genotypic testing revealed resistance to ganciclovir, foscarnet, or cidofovir in 56% of patients receiving maribavir and 68% receiving IAT, including 9 newly phenotyped mutations. Among them, 63% (maribavir) and 21% (IAT) were treatment responders. Detected baseline maribavir resistance mutations were UL27 L193F (n = 1) and UL97 F342Y (n = 3). Posttreatment, emergent maribavir resistance mutations were detected in 60 (26%) of those randomized to maribavir, including 49 (48%) of 103 nonresponders and 25 (86%) of the 29 nonresponders where viral DNA initially cleared then rebounded while on maribavir. The most common maribavir resistance mutations were UL97 T409M (n = 34), H411Y (n = 26), and C480F (n = 21), first detected 26 to 130 (median 56) days after starting maribavir.

CONCLUSIONS

Baseline maribavir resistance was rare. Drug resistance to standard cytomegalovirus antivirals did not preclude treatment response to maribavir. Rebound in plasma cytomegalovirus DNA while on maribavir strongly suggests emerging drug resistance.

CLINICAL TRIALS REGISTRATION

NCT02931539.

Slaying the "Troll of Transplantation"-new frontiers in cytomegalovirus management: A report from the CMV International Symposium 2023

The 2023 International CMV Symposium took place in Barcelona in May 2023. During the 2-day meeting, delegates and faculty discussed the ongoing challenge of managing the risk of cytomegalovirus infection (the Troll of Transplantation) after solid organ or hematopoietic cell transplantation. Opportunities to improve outcomes of transplant recipients by applying advances in antiviral prophylaxis or pre-emptive therapy, immunotherapy, and monitoring of cell-mediated immunity to routine clinical practice were debated and relevant educational clinical cases presented. This review summarizes the presentations, cases, and discussions from the meeting and describes how further advances are needed before the Troll of Transplantation is slain.

Management of Cytomegalovirus Infections in the Era of the Novel Antiviral Players, Letermovir and Maribavir

Cytomegalovirus (CMV) infections may increase morbidity and mortality in immunocompromised patients. Until recently, standard antiviral drugs against CMV were limited to viral DNA polymerase inhibitors (val)ganciclovir, foscarnet and cidofovir with a risk for cross-resistance. These drugs may also cause serious side effects. This narrative review provides an update on new antiviral agents that were approved for the prevention and treatment of CMV infections in transplant recipients. Letermovir was approved in 2017 for CMV prophylaxis in CMV-seropositive adults who received an allogeneic hematopoietic stem cell transplant. Maribavir followed four years later, with an indication in the treatment of adult and pediatric transplant patients with refractory/resistant CMV disease. The target of letermovir is the CMV terminase complex (constituted of pUL56, pUL89 and pUL51 subunits). Letermovir prevents the cleavage of viral DNA and its packaging into capsids. Maribavir is a pUL97 kinase inhibitor, which interferes with the assembly of capsids and the egress of virions from the nucleus. Both drugs have activity against most CMV strains resistant to standard drugs and exhibit favorable safety profiles. However, high-level resistance mutations may arise more rapidly in the UL56 gene under letermovir than low-grade resistance mutations. Some mutations emerging in the UL97 gene under maribavir can be cross-resistant with ganciclovir. Thus, letermovir and maribavir now extend the drug arsenal available for the management of CMV infections and their respective niches are currently defined.

Unlocking the Pharmacological Potential of Benzimidazole Derivatives: A Pathway to Drug Development

Heterocyclic molecules have fascinated a massive interest in medicinal chemistry. They are heterocyclic compounds that have gained significance due to their diverse variety of pharmacological activities. Benzimidazole is a heterocyclic compound consisting of benzene and imidazole rings. The ease of synthesis and the structural versatility of benzimidazole make it a promising scaffold for drug development. Many biological actions of benzimidazole derivatives have been well documented, including antibacterial, antiviral, anticancer, anti-inflammatory, antitubercular, and anthelmintic properties. The mechanism of action of benzimidazole derivatives varies with their chemical structure and target enzyme. This review has explored numerous methods for producing benzimidazole derivatives as well as a broad range of pharmacological activities. SAR investigations are also discussed in this review as they provide crucial details regarding the essential structural qualities that benzimidazole derivatives must have in order to be biologically active, which could aid in the rational design of new drug candidates. Benzimidazole scaffold is an exclusive structure in drug design and discovery. Many new pharmaceutical drugs containing benzimidazole are anticipated to be available within the next ten years as a result of the extensive therapeutic applications of benzimidazole and its derivatives. This review inspired many researchers to develop more biologically active compounds bearing benzimidazole, expanding the scope of finding a remedy for other diseases. From this study, we concluded that 2-substituted benzimidazole was considered more extensively by researchers.

Maribavir: Mechanism of action, clinical, and translational science

Maribavir is an oral benzimidazole riboside for treatment of post-transplant cytomegalovirus (CMV) infection/disease that is refractory to prior antiviral treatment (with or without resistance). Through competitive inhibition of adenosine triphosphate, maribavir prevents the phosphorylation actions of UL97 to inhibit CMV DNA replication, encapsidation, and nuclear egress. Maribavir is active against CMV strains with viral DNA polymerase mutations that confer resistance to other CMV antivirals. After oral administration, maribavir is rapidly and highly absorbed (fraction absorbed >90%). The approved dose of 400 mg twice daily (b.i.d.) achieves a steady-state area under the curve per dosing interval of 128 h*μg/mL and trough concentration of 4.90 μg/mL (13.0 μM). Maribavir is highly bound to human plasma proteins (98%) with a small apparent volume of distribution of 27.3 L. Maribavir is primarily cleared by hepatic CYP3A4 metabolism; its major metabolite, VP44669 (pharmacologically inactive), is excreted in the urine and feces. There is no clinically relevant impact on maribavir pharmacokinetics by age, sex, race/ethnicity, body weight, transplant type, or hepatic/renal impairment status. In phase II dose-ranging studies, maribavir showed similar rates of CMV viral clearance across 400, 800, or 1200 mg b.i.d. groups, ranging from 62.5-70% in study 202 (NCT01611974) and 74-83% in study 203 (EudraCT 2010-024247-32). In the phase III SOLSTICE trial (NCT02931539), maribavir 400 mg b.i.d. demonstrated superior CMV viremia clearance at week 8 versus investigator-assigned treatments, with lower treatment discontinuation rates. Dysgeusia, nausea, vomiting, and diarrhea were commonly experienced adverse events among patients treated with maribavir in clinical trials.

Refractory cytomegalovirus infections in Chinese patients receiving allogeneic hematopoietic cell transplantation: a review of the literature

In the absence of prophylactic therapy, cytomegalovirus (CMV) viremia is a common complication following allogeneic hematopoietic cell transplantation (allo-HCT) and represents a significant cause of morbidity and mortality. Approximately 25% of allo-HCT happen in China, where the development and refinement of the 'Beijing protocol' has enabled frequent and increasing use of haploidentical donors. However, refractory CMV infection (an increase by >1 log10 in blood or serum CMV DNA levels after at least 2 weeks of an appropriately dosed anti-CMV medication) is more common among patients with haploidentical donors than with other donor types and has no established standard of care. Here, we review the literature regarding refractory CMV infection following allo-HCT in China.

Anti-CMV therapy, what next? A systematic review

Human cytomegalovirus (HCMV) is one of the main causes of serious complications in immunocompromised patients and after congenital infection. There are currently drugs available to treat HCMV infection, targeting viral polymerase, whose use is complicated by toxicity and the emergence of resistance. Maribavir and letermovir are the latest antivirals to have been developed with other targets. The approval of letermovir represents an important innovation for CMV prevention in hematopoietic stem cell transplant recipients, whereas maribavir allowed improving the management of refractory or resistant infections in transplant recipients. However, in case of multidrug resistance or for the prevention and treatment of congenital CMV infection, finding new antivirals or molecules able to inhibit CMV replication with the lowest toxicity remains a critical need. This review presents a range of molecules known to be effective against HCMV. Molecules with a direct action against HCMV include brincidofovir, cyclopropavir and anti-terminase benzimidazole analogs. Artemisinin derivatives, quercetin and baicalein, and anti-cyclooxygenase-2 are derived from natural molecules and are generally used for different indications. Although they have demonstrated indirect anti-CMV activity, few clinical studies were performed with these compounds. Immunomodulating molecules such as leflunomide and everolimus have also demonstrated indirect antiviral activity against HCMV and could be an interesting complement to antiviral therapy. The efficacy of anti-CMV immunoglobulins are discussed in CMV congenital infection and in association with direct antiviral therapy in heart transplanted patients. All molecules are described, with their mode of action against HCMV, preclinical tests, clinical studies and possible resistance. All these molecules have shown anti-HCMV potential as monotherapy or in combination with others. These new approaches could be interesting to validate in clinical trials.

Antimicrobials in patients with hematologic malignancies and recipients of hematopoietic cell transplantation and other cellular therapies

BACKGROUND

Appropriate use of antimicrobials for hematologic malignancy, hematopoietic stem cell transplant recipients, and other cellular therapies is vital, with infection causing significant morbidity and mortality in this unique population of immunocompromised hosts. However, often in this population the choice and management of antimicrobial therapy is complex. When selecting an antimicrobial agent, key considerations include the need for dose adjustments due to renal or hepatic impairment, managing drug interactions, the potential for additive drug toxicity among those receiving polypharmacy and therapeutic drug monitoring. Other factors include leveraging pharmacodynamic principles to enable optimization of directed therapy against challenging pathogens, as well as judicious use of antimicrobials to limit drug resistance and adverse drug reactions.

SUMMARY

This review summarizes the clinical considerations for commonly used antimicrobials in this setting, including antibacterial, antiviral, and antifungal agents.

New Treatment Options for Refractory/Resistant CMV Infection

Despite advances in monitoring and treatment, cytomegalovirus (CMV) infections remain one of the most common complications after solid organ transplantation (SOT). CMV infection may fail to respond to standard first- and second-line antiviral therapies with or without the presence of antiviral resistance to these therapies. This failure to respond after 14 days of appropriate treatment is referred to as "resistant/refractory CMV." Limited data on refractory CMV without antiviral resistance are available. Reported rates of resistant CMV are up to 18% in SOT recipients treated for CMV. Therapeutic options for treating these infections are limited due to the toxicity of the agent used or transplant-related complications. This is often the challenge with conventional agents such as ganciclovir, foscarnet and cidofovir. Recent introduction of new CMV agents including maribavir and letermovir as well as the use of adoptive T cell therapy may improve the outcome of these difficult-to-treat infections in SOT recipients. In this expert review, we focus on new treatment options for resistant/refractory CMV infection and disease in SOT recipients, with an emphasis on maribavir, letermovir, and adoptive T cell therapy.

Safety and efficacy of weight-based ganciclovir dosing strategies in overweight/obese patients

BACKGROUND

The management of cytomegalovirus (CMV) is particularly challenging as both CMV and its usual first-line treatment, ganciclovir, are associated with neutropenia. Ganciclovir dosing is weight-based, most commonly utilizing total body weight (TBW). The subsequent high doses of ganciclovir in overweight/obese patients may increase the risk of toxicity. Utilizing adjusted body weight (AdjBW) dosing may help mitigate this risk. Therefore, the objective of this study was to evaluate the difference in toxicity and efficacy between TBW and AdjBW ganciclovir dosing strategies in overweight/obese patients.

METHODS

This retrospective study conducted safety and efficacy analyses of ganciclovir courses (≥72 h) used as CMV treatment. The primary safety outcome was the incidence of neutropenia (absolute neutrophil count <1000 cells/μL), and the primary efficacy outcome was a 2-log decrease in CMV polymerase chain reaction within 4 weeks following ganciclovir initiation. In both analyses, courses were excluded in which ganciclovir was dosed outside of specified renal dosing parameters for >20% of the course.

RESULTS

Among the 253 courses in the safety cohort, there was no difference in the incidence of neutropenia (17.4% vs. 13.5%, p = .50) in AdjBW compared to TBW dosing. In the 62 courses evaluating efficacy, there was no statistical difference between AdjBW and TBW dosing (60.0% vs. 45.2%, p = .28). No subgroups were identified in which AdjBW dosing was advantageous.

CONCLUSION

Utilization of AdjBW ganciclovir dosing did not result in decreased neutropenia or treatment efficacy as compared to TBW dosing. Further studies with larger patient populations would be beneficial to confirm these findings.

Oral antiviral drugs for treatment of cytomegalovirus in transplant recipients

BACKGROUND

Cytomegalovirus (CMV) is an opportunistic pathogen responsible for substantial morbidity after solid organ transplantation and haematopoietic stem cell transplantation. Treatment of CMV disease involves a two-pronged approach with antiviral drug treatment coupled with strategies to minimize the intensity of immune suppression.

OBJECTIVES

This narrative review examines the evidence for the current treatment of CMV disease in transplant recipients, including the use of oral antiviral drugs.

SOURCES

Literature search was performed on PubMed with keywords cytomegalovirus, transplantation, ganciclovir, valganciclovir, maribavir, letermovir, cidofovir, and foscarnet.

CONTENT

Intravenous and oral valganciclovir are the standard first-line treatment of cytomegalovirus disease after transplantation. Oral maribavir has demonstrated superior efficacy and safety over CMV DNA polymerase inhibitors for the treatment of refractory or resistant CMV infection. Transplant patients with severe and life-threatening CMV disease, those with very high viral load, and patients with impaired gastrointestinal absorption should still be treated initially with intravenous antiviral drugs, including ganciclovir and foscarnet. Criteria for the safe transition from intravenous therapies to oral antiviral drugs include achieving clinical improvement and satisfactory decline in viral load. Recurrence of CMV viremia and disease is common, particularly among transplant patients who are lymphopenic and have impaired CMV-specific immunity.

IMPLICATIONS

Oral antiviral drugs for the treatment of CMV infection and disease in transplant recipients have improved the CMV landscape, because they reduce the cost and mitigate the inconvenience and risks related to prolonged hospitalization and the need for long-term intravascular access. However, their antiviral efficacy should be complemented by an intentional strategy of reducing the degree of immune suppression to allow for immunologic recovery that ensures durable control of CMV infection.

Pharmacokinetics and Safety Evaluation of Maribavir in Healthy Japanese and Matched White Participants: A Phase I, Open-Label Study

This phase I study compared pharmacokinetics and safety of maribavir in Japanese and White participants, and evaluated dose proportionality in Japanese participants. Under fasting conditions, 12 healthy adult participants of Japanese descent and 12 matched White participants received a single 400-mg dose of maribavir. Japanese participants received 2 further doses of maribavir: 200 mg and 800 mg, or 800 mg and 200 mg, separated by a ≥72-hour washout period. Serial blood samples were collected up to 24 hours after dosing for pharmacokinetic assessments. Following the 400-mg dose, the geometric mean ratios (90% confidence interval) of Japanese versus White participants were 110% (91.7%-133%) for maximum plasma concentration, 122% (96.8%-155%) for area under the plasma concentration-time curve (AUC) from time of dosing to the last measurable concentration, and 125% (98.0%-160%) for AUC extrapolated to infinity. In Japanese participants, maribavir AUC extrapolated to infinity and AUC from time of dosing to the last measurable concentration increased in a dose-proportional fashion over 200-800 mg; maximum plasma concentration increased less than dose proportionally. Seven participants reported treatment-emergent adverse events (TEAEs; Japanese participants, 400 mg: 2 [16.7%], 200 mg: 1 [8.3%]; White participants, 400 mg: 4 [33.3%]), all mild and most commonly dysgeusia. No serious TEAEs or TEAEs leading to discontinuation were reported. This study demonstrated higher maribavir systemic exposure in Japanese than White participants and similar safety outcomes. This difference in exposure is not considered clinically important and its significance remains to be determined.

Synthesis of 1-[ω-(Bromophenoxy)alkyl]-3-naphthalenylmethyl Derivatives of Uracil and Their Analogues As Probable Inhibitors of Human Cytomegalovirus Replication

The synthesis of a new series of 1-[ω-(bromophenoxy)alkyl]-uracil derivatives containing in position 3 naphthalen-1-yl-, naphthalen-2-yl-, 1-bromonaphthalen-2-ylmethyl, benzyl, and anthracene 9-methyl fragment was carried out. The antiviral properties of the synthesized compounds were studied against human cytomegalovirus. It was found that the compound that contained a bridge of five methylene groups has a high anti-cytomegalovirus activity in vitro.

Opportunistic Infections Post-Lung Transplantation: Viral, Fungal, and Mycobacterial

Opportunistic infections are a leading cause of lung transplant recipient morbidity and mortality. Risk factors for infection include continuous exposure of the lung allograft to the external environment, high levels of immunosuppression, impaired mucociliary clearance and decreased cough reflex, and impact of the native lung microbiome in single lung transplant recipients. Infection risk is mitigated through careful pretransplant screening of recipients and donors, implementation of antimicrobial prophylaxis strategies, and routine surveillance posttransplant. This review describes common viral, fungal, and mycobacterial infectious after lung transplant and provides recommendations on prevention and treatment.

Population pharmacokinetic modeling and simulation of maribavir to support dose selection and regulatory approval in adolescents with posttransplant refractory cytomegalovirus

Maribavir was approved by the US Food and Drug Administration for the treatment of patients aged ≥12 years and weighing ≥35 kg with posttransplant cytomegalovirus infection/disease refractory (with/without resistance) to valganciclovir, ganciclovir, cidofovir, or foscarnet, with an oral dose of 400 mg twice daily. With no pediatric clinical data available and difficulty in trial recruitment, population pharmacokinetic modeling and simulations were conducted to predict the pharmacokinetics and inform maribavir dosing in adolescents.

Optimizing the treatment of cytomegalovirus infection in allo-HSCT recipients

INTRODUCTION

Cytomegalovirus (CMV) infection continues to negatively impact the prognosis after allogeneic hematopoietic stem cell transplantation (allo-HSCT), even with active monitoring and preemptive strategies. Recent progress in pharmacology, immunotherapy, and vaccines has improved the strategy of CMV management.

AREAS COVERED

We summarized recent advances in managing CMV infection post allo-HSCT, including diagnosis, prophylaxis, and treatment. In this review, we mainly focused on approaches that have optimized or might optimize the management of CMV infection after allo-HSCT.

EXPERT OPINION

In our opinion, optimized management covers aspects including the serial monitoring of CMV-DNA and CMI, an accurate diagnosis, effective prophylaxis, and a rational preemptive therapy integrating antiviral drugs and cell therapies. Strategies based on the understanding of CMV pathogenesis and CMV-related immune reconstitution after allo-HSCT will be a direction in future studies.

Maribavir Pharmacokinetics and Safety in Participants With Moderate Hepatic Impairment: A Phase 1, Open-Label, Single-Dose, Parallel Group Study

Maribavir, an orally bioavailable antiviral, has shown superior activity against posttransplant cytomegalovirus infection compared with conventional antivirals. It is primarily metabolized in the liver. This open-label, single-center study evaluated the effect of hepatic impairment on the pharmacokinetics of maribavir in nontransplant participants. A single 200-mg dose of maribavir was administered orally under fasting conditions to participants with moderate hepatic impairment (Child-Pugh class B) (n = 10) and healthy controls (n = 10) matched for age, weight, sex, and smoking status. Compared with participants with normal hepatic function, maximum plasma concentration (C_max ) and area under the plasma concentration-time curve (AUC) from time 0 to infinity values for maribavir in participants with moderate hepatic impairment were 1.346-fold (90%CI of geometric mean ratio, 1.091-1.660) and 1.261-fold (0.889-1.787) higher, respectively. However, C_max and AUC values for unbound maribavir were comparable. For VP 44469, the main metabolite of maribavir, the C_max and AUC from time 0 to infinity values were 1.190-fold (0.836-1.693) and 1.309-fold (1.007-1.702) higher, respectively, in participants with moderate hepatic impairment. In total, 7 mild treatment-emergent adverse events were reported, all in the moderate hepatic impairment group. Dysgeusia was the most frequently reported treatment-emergent adverse event, at a frequency of 50%. These results indicated that total maribavir concentrations were mildly increased in participants with moderate hepatic impairment, while unbound concentrations were unaffected. Similar maribavir pharmacokinetics in participants with moderate hepatic impairment and normal hepatic function suggest that dose adjustment may not be required for patients with moderate hepatic impairment.

Optimizing Antiviral Dosing for HSV and CMV Treatment in Immunocompromised Patients

Herpes simplex virus (HSV) and cytomegalovirus (CMV) are DNA viruses that are common among humans. Severely immunocompromised patients are at increased risk of developing HSV or CMV disease due to a weakened immune system. Antiviral therapy can be challenging because these drugs have a narrow therapeutic window and show significant pharmacokinetic variability. Above that, immunocompromised patients have various comorbidities like impaired renal function and are exposed to polypharmacy. This scoping review discusses the current pharmacokinetic (PK) and pharmacodynamic (PD) knowledge of antiviral drugs for HSV and CMV treatment in immunocompromised patients. HSV and CMV treatment guidelines are discussed, and multiple treatment interventions are proposed: early detection of drug resistance; optimization of dose to target concentration by therapeutic drug monitoring (TDM) of nucleoside analogs; the introduction of new antiviral drugs; alternation between compounds with different toxicity profiles; and combinations of synergistic antiviral drugs. This research will also serve as guidance for future research, which should focus on prospective evaluation of the benefit of each of these interventions in randomized controlled trials.

Cytomegalovirus infection in transplant recipients: newly approved additions to our armamentarium

BACKGROUND

The burden that cytomegalovirus (CMV) portends for haematopoietic and solid-organ transplant recipients cannot be understated. Valganciclovir and ganciclovir have successfully been used for prevention and treatment of CMV infections, although with serious side effects such as leucopenia and some development of resistance. Until recently, available therapies for ganciclovir-resistant CMV have significant toxicities. Although advances have been made in the field, the unmet medical needs for effective and well-tolerated therapies are significant.

OBJECTIVES

This review aims to summarise the current and emerging CMV antiviral drugs and discusses future perspectives in the field.

SOURCES

We searched for relevant articles with pertinent keywords: "Cytomegalovirus OR CMV", "Transplant" and "Antiviral". Articles published after 2019 were given preference. Articles were reviewed by the authors for relevance and impact to the subject of interest.

CONTENT

We outline in this review current advances in prophylaxis of CMV infection with letermovir, breakthrough CMV infections while on or after prophylaxis, the development of resistant and refractory CMV infections, and the newly approved anti-CMV agent, maribavir, in haematopoietic and solid-organ transplant recipients.

IMPLICATIONS

Prevention of CMV infections after transplant has improved greatly over the past few years. Despite major advancements, breakthrough CMV infections and development of refractory and resistant CMV infections remain major complications post transplantation. We highlight emerging therapeutics that tolerably and effectively prevent and treat CMV infections, especially refractory and resistant cases.

Therapeutic Implications of the Microbial Hypothesis of Mental Illness

There is increasingly compelling evidence that microorganisms may play an etiological role in the emergence of mental illness in a subset of the population. Historically, most work has focused on the neurotrophic herpesviruses, herpes simplex virus type 1 (HSV-1), cytomegalovirus (CMV), and Epstein-Barr virus (EBV) as well as the protozoan, Toxoplasma gondii. In this chapter, we provide an umbrella review of this literature and additionally highlight prospective studies that allow more mechanistic conclusions to be drawn. Next, we focus on clinical trials of anti-microbial medications for the treatment of psychiatric disorders. We critically evaluate six trials that tested the impact of anti-herpes medications on inflammatory outcomes in the context of a medical disorder, nine clinical trials utilizing anti-herpetic medications for the treatment of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) or schizophrenia, and four clinical trials utilizing anti-parasitic medications for the treatment of schizophrenia. We then turn our attention to evidence for a gut dysbiosis and altered microbiome in psychiatric disorders, and the potential therapeutic effects of probiotics, including an analysis of more than 10 randomized controlled trials of probiotics in the context of schizophrenia, bipolar disorder (BD), and major depressive disorder (MDD).

Maribavir

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Challenges, Recent Advances and Perspectives in the Treatment of Human Cytomegalovirus Infections

Human cytomegalovirus (HCMV) is ubiquitous worldwide and elicits global health problems. The diseases associated with HCMV are a serious threat to humans, especially for the sick, infant, elderly and immunocompromised/immunodeficient individuals. Although traditional antiviral drugs (e.g., ganciclovir, valganciclovir, cidofovir, foscarnet) can be used to treat or prevent acute HCMV infections, their efficacy is limited because of toxicity, resistance issues, side effects and other problems. Fortunately, novel drugs (e.g., letermovir and maribavir) with less toxicity and drug/cross-resistance have been approved and put on the market in recent years. The nucleic acid-based gene-targeting approaches including the external guide sequences (EGSs)-RNase, the clustered regularly interspaced short palindromic repeats (CRISPRs)/CRISPRs-associated protein 9 (Cas9) system and transcription activator-like effector nucleases (TALENs) have been investigated to remove both lytic and latent CMV in vitro and/or in vivo. Cell therapy including the adoptive T cell therapy (ACT) and immunotherapy have been tried against drug-resistant and recurrent HCMV in patients receiving hematopoietic stem cell transplantation (HSCT) or solid organ transplant (SOT), and they have also been used to treat glioblastoma (GBM) associated with HCMV infections. These newly developed antiviral strategies are expected to yield fruitful results and make a significant contribution to the treatment of HCMV infections. Despite this progress, the nucleic acid-based gene-targeting approaches are still under study for basic research, and cell therapy is adopted in a small study population size or only successful in case reports. Additionally, no current drugs have been approved to be indicated for latent infections. Therefore, the next strategy is to develop antiviral strategies to elevate efficacy against acute and/or latent infections and overcome challenges such as toxicity, resistance issues, and side effects. In this review, we would explore the challenges, recent advances and perspectives in the treatment of HCMV infections. Furthermore, the suitable therapeutic strategies as well as the possibility for compassionate use would be evaluated.

Cytomegalovirus in the transplant setting: Where are we now and what happens next? A report from the International CMV Symposium 2021

The CMV Symposium in September 2021 was an international conference dedicated to cytomegalovirus (CMV) infection after solid organ or hematopoietic stem cell transplantation. This review provides an overview of the presentations given by the expert faculty, supplemented with educational clinical cases. Topics discussed include CMV epidemiology and diagnosis, the burden of CMV infection and disease, CMV-specific immunity and management of CMV in transplant settings. Major advances in the prevention and treatment of CMV in the past decade and increased understanding of CMV immunity have led to improved patient outcomes. In the future, management algorithms may be individualized based on the transplant recipient's immune profile, which will mark the start of a new era for patients with CMV.

Adoptive Immunotherapy for Prophylaxis and Treatment of Cytomegalovirus Infection

Cytomegalovirus (CMV), a member of the Herpesviridae family, is frequent among hematopoietic cell transplant (HCT) and solid organ transplant (SOT) recipients in absence of antiviral prophylaxis, and is a major cause of morbidity and mortality in these vulnerable populations. Antivirals such ganciclovir, valganciclovir, and foscarnet are the backbone therapies, however drug toxicity and antiviral resistance may render these agents suboptimal in treatment. Newer therapies such as letermovir and maribavir have offered additional approaches for antiviral prophylaxis as well as treatment of drug resistant CMV infection, though may be limited by cost, drug intolerance, or toxicity. Adoptive immunotherapy, the transfer of viral specific T-cells (VSTs), offers a new approach in treatment of drug-resistant or refractory viral infections, with early clinical trials showing promise with respect to efficacy and safety. In this review, we will discuss some of the encouraging results and challenges of widespread adoption of VSTs in care of immunocompromised patients, with an emphasis on the clinical outcomes for treatment and prophylaxis of CMV infection among high-risk patient populations.

Diagnosis and treatment for the early stage of cytomegalovirus infection during hematopoietic stem cell transplantation

Cytomegalovirus (CMV) infection remains a frequent complication after hematopoietic stem cell transplantation (HSCT) and causes significant morbidity and mortality in transplantation recipients. In this review, we highlight the role of major risk factors that are associated with the incidence of CMV infection. Advances in immunosurveillance may predict CMV infection, allowing early interventions to prevent severe infection. Furthermore, numerous therapeutic strategies against CMV infection after HSCT are summarized. A comprehensive understanding of the current situation of CMV treatment may provide a hint for clinical practice and even promote the development of novel strategies for precision medicine.

New Perspectives on Antimicrobial Agents: Maribavir

Maribavir was approved by the U.S. Food and Drug Administration in November 2021 for the treatment of adult and pediatric patients with post-transplant cytomegalovirus (CMV) infection/disease that is refractory to treatment (with or without genotypic resistance) with ganciclovir, valganciclovir, cidofovir, or foscarnet. Maribavir is an oral benzimidazole riboside with potent and selective multimodal anti-CMV activity. It utilizes a novel mechanism of action which confers activity against CMV strains that are resistant to traditional anti-CMV agents, and also offers a more favorable safety profile relative to the dose-limiting side effects of previously available therapies. Maribavir was initially studied as an agent for CMV prophylaxis in solid organ and hematopoietic stem cell recipients, but initial phase III trials failed to meet clinical efficacy endpoints. It has been more recently studied as a therapeutic agent at higher doses for refractory-resistant (R-R) CMV infections with favorable outcomes. After an overview of maribavir's chemistry and clinical pharmacology, this review will summarize clinical efficacy, safety, tolerability, and resistance data associated with maribavir therapy.

Maribavir for the Management of Cytomegalovirus in Adult Transplant Recipients: A Review of the Literature and Practical Considerations

OBJECTIVE

To review the efficacy and safety of maribavir for management of cytomegalovirus (CMV) in solid organ transplant recipients.

DATA SOURCES

A literature search of PubMed and the Cochrane Controlled Trials Register (1960 to early July 2022) was performed using the following search terms: maribavir, 1263W94, and cytomegalovirus.

STUDY SELECTION AND DATA EXTRACTION

All relevant English-language studies were reviewed and considered, with a focus on phase 3 trials.

DATA SYNTHESIS

Maribavir, an orally available benzimidazole riboside with minimal adverse effects, was originally studied for universal prophylaxis in phase 3 trials but failed to demonstrate noninferiority over placebo and oral ganciclovir. It was effective for preemptive treatment in a dose-finding Phase 2 study. Maribavir is FDA approved for treatment of refractory/resistant CMV infection based on improved response rate at 8 weeks compared with investigator-assigned therapy (IAT) when initiated at median viral loads less than approximately 10 000 IU/mL (55.7% vs 23.9%, P < 0.001). Recurrence after 8-week treatment for refractory/resistant CMV was high (maribavir 50% vs IAT 39%). Significant drug interactions exist and must be managed by a pharmacotherapy expert to prevent harm.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

The addition of maribavir to the antiviral armamentarium should improve the management of refractory/resistant CMV, allowing early transition from toxic, high-cost, intravenous agents such as foscarnet and outpatient management. Optimal timing of initiation, duration, and potential alternative uses are unclear.

CONCLUSION

Future studies are needed to fully elucidate the role of maribavir in the management of CMV after transplant.

Cytomegalovirus Management in Solid Organ Transplant Recipients: A Pre-COVID-19 Survey From the Working Group of the European Society for Organ Transplantation

Infections are leading causes of morbidity/mortality following solid organ transplantation (SOT) and cytomegalovirus (CMV) is among the most frequent pathogens, causing a considerable threat to SOT recipients. A survey was conducted 19 July–31 October 2019 to capture clinical practices about CMV in SOT recipients (e.g., how practices aligned with guidelines, how adequately treatments met patients’ needs, and respondents’ expectations for future developments). Transplant professionals completed a ∼30-minute online questionnaire: 224 responses were included, representing 160 hospitals and 197 SOT programs (41 countries; 167[83%] European programs). Findings revealed a heterogenous approach to CMV diagnosis and management and, sometimes, significant divergence from international guidelines. Valganciclovir prophylaxis (of variable duration) was administered by 201/224 (90%) respondents in D+/R− SOT and by 40% in R+ cases, with pre-emptive strategies generally reserved for R+ cases: DNA thresholds to initiate treatment ranged across 10–10,000 copies/ml. Ganciclovir-resistant CMV strains were still perceived as major challenges, and tailored treatment was one of the most important unmet needs for CMV management. These findings may help to design studies to evaluate safety and efficacy of new strategies to prevent CMV disease in SOT recipients, and target specific educational activities to harmonize CMV management in this challenging population.

In vitro activity of letermovir against human cytomegalovirus isolates with different drug susceptibility phenotypes

Letermovir (LTV) is approved for the prophylaxis of human cytomegalovirus (HCMV) infection in adult seropositive recipients of an allogeneic hematopoietic stem cell transplant. Here, we report on the in vitro activity of LTV against a large panel of clinical HCMV isolates and recombinant viruses with different drug susceptibility phenotypes to currently-approved DNA polymerase inhibitors or maribavir. No pre-existing mutations conferring resistance to LTV were detected by Sanger sequencing in clinical HCMV isolates susceptible or resistant to DNA polymerases inhibitors. The susceptibility of LTV against the different recombinant HCMV mutants with amino acid substitutions in the UL97 kinase or in the UL54 DNA polymerase was similar to that of the wild type virus. LTV was also effective against recombinant HCMV harboring UL97 mutations conferring resistance to maribavir.

40 Years after the Registration of Acyclovir: Do We Need New Anti-Herpetic Drugs?

Herpes simplex virus types 1 and 2 HSV1 and 2, namely varicella-zoster VZV and cytomegalovirus CMV, are among the most common pathogens worldwide. They remain in the host body for life. The course of infection with these viruses is often asymptomatic or mild and self-limiting, but in immunocompromised patients, such as solid organ or bone marrow transplant recipients, the course can be very severe or even life-threatening. Unfortunately, in the latter group, the highest percentage of infections with strains resistant to routinely used drugs is observed. On the other hand, frequent recurrences of genital herpes can be a problem even in people with normal immunity. Genital herpes also increases the risk of acquiring sexually transmitted diseases, including HIV infection and, if present in pregnant women, poses a risk to the fetus and newborn. Even more frequently than herpes simplex, congenital infections can be caused by cytomegalovirus. We present the most important anti-herpesviral agents, the mechanisms of resistance to these drugs, and the associated mutations in the viral genome. Special emphasis was placed on newly introduced drugs such as maribavir and brincidofovir. We also briefly discuss the most promising substances in preclinical testing as well as immunotherapy options and vaccines currently in use and under investigation.

Evaluating the Safety of Maribavir for the Treatment of Cytomegalovirus

Purpose of Review

Cytomegalovirus (CMV) infections are a common complication in solid organ (SOT) and hematopoietic stem cell transplant (HSCT) recipients, leading to increased morbidity and mortality. Currently available treatment options have reduced the burden of infection, but utilization of these agents can be limited by toxicities such as nephrotoxicity and/or myelosuppression as well as emergence of resistance. The expansion of our current armamentarium towards CMV infection is crucial. Here, we review an emerging therapy, maribavir, and the safety and efficacy of this potential new agent for the prophylaxis and treatment of CMV infections including resistant/refractory disease.

Recent Findings

Maribavir is a novel agent with CMV activity approved by Federal Food and Drug Administration (FDA) in December 2021 for resistant/refractory disease. Compared to currently available treatment for CMV infection, maribavir has a unique mechanism of action, retains activity against most (val)ganciclovir resistant strains, provides a more predictable pharmacokinetic profile, and fewer severe toxicities. Maribavir has been studied in phase 2 and 3 studies with ongoing phase 3 studies. While maribavir failed to meet the primary endpoints in the initial phase 3 study for prophylaxis therapy in allogeneic-HSCT and liver transplant recipients, results from the phase 2 study when used for pre-emptive therapy after HSCT show similar efficacy to valganciclovir, and results from the phase 3 study examining resistant/refractory disease demonstrate superiority to investigator-initiated therapy of (val)ganciclovir, foscarnet, or cidofovir.

Summary

Maribavir provides a new agent for the management of resistant/refractory CMV infection. Results of the recently published phase 3 study provide further insight into the role of this novel therapy.

Maribavir: First Approval

Maribavir (LIVTENCITY^TM), a cytomegalovirus (CMV) enzyme pUL97 kinase inhibitor, is being developed by Takeda Pharmaceuticals for the treatment of CMV infections. Maribavir was recently approved in the USA for the treatment of post-transplant CMV infection/disease that is refractory to treatment (with or without genotypic resistance) with ganciclovir, valganciclovir, cidofovir or foscarnet in adults and paediatric (≥ 12 years of age and weighing ≥ 35 kg) patients. This article summarizes the milestones in the development of maribavir leading to this first approval for CMV infections.