Independent educational summary. This page summarises the PMDA document “Consideration in the development of drugs for hypertrophic cardiomyopathy(Early Consideration)” in plain language. Clinical Biostats created it by editing and summarising the document; it is not an official PMDA publication and is not legal or regulatory advice. Consult the official document: PMDA provides the English version for reference purposes, and the Japanese original prevails if the two differ.
In Plain Language
This document discusses clinical development of drugs for hypertrophic cardiomyopathy (HCM), a condition in which the heart muscle becomes thickened and may have difficulty relaxing. It distinguishes obstructive HCM (oHCM), where blood flow out of the left ventricle is obstructed, from non-obstructive HCM (nHCM), and explains that development plans should account for differences between these phenotypes. For confirmatory trials, it generally describes randomized, double-blind comparisons with an appropriate control, while recognizing that small patient numbers can make trials using survival events difficult. When survival-related outcomes cannot feasibly be the primary endpoint, PMDA recommends peak oxygen uptake as a primary endpoint, alongside other measures that help assess symptoms, survival-related outcomes, and, for oHCM, the left ventricular outflow tract pressure gradient. These considerations aim to support development that evaluates treatment effects and safety in a rare disease while taking account of phenotype, existing treatment, and the practical limits of trial recruitment.
What This Guidance Covers
The document sets out PMDA’s current considerations for clinical development strategies for HCM therapeutics in Japan. It addresses overall development planning and confirmatory trials, including study design, efficacy endpoints, evaluation period, study population, and dosage and administration. It discusses both oHCM and nHCM, and it also notes that HCM occurs in pediatric patients.
The document describes HCM as hypertrophy of the left or right ventricular myocardium, with impairment of left ventricular diastolic function due to the hypertrophy. It states that clinical diagnosis is made when echocardiography or cardiac magnetic resonance imaging shows a maximum left ventricular wall thickness of at least 15 mm, or at least 13 mm in individuals with a family history of HCM, and other diseases that may cause myocardial hypertrophy are excluded. The document does not present a comprehensive clinical-care guideline; its stated purpose is to present current considerations for clinical development strategies.
The document situates drug development in a treatment context where pharmacotherapy in Japan for both phenotypes is primarily symptomatic. It names β-blockers and calcium channel blockers as treatments used to improve symptoms, and sodium channel inhibitors as treatments that may also be used in oHCM. It notes that the cardiac myosin inhibitor mavacamten has been approved as a treatment acting directly on the disease mechanism, with an indication limited to oHCM. For some patients with oHCM whose symptoms are not sufficiently controlled by pharmacological treatment, non-pharmacological interventions such as septal reduction therapy may be considered as alternatives.
Why It Matters
The document identifies two related development challenges. First, HCM is rare, and the number of patients is limited; the introduction reports 4,388 patients in Japan based on the number of Intractable Disease Medical Treatment Recipient Certificates issued as of fiscal year 2023. This can make it difficult to conduct confirmatory trials solely within Japan. Second, oHCM and nHCM differ in pathophysiology and may have different prognoses, so pooling them without appropriate consideration may not reflect their distinct characteristics.
The treatment goal is improvement in long-term prognosis. However, the document notes that limited patient numbers may make confirmatory trials with mortality-related events as primary efficacy endpoints difficult. It therefore discusses an alternative primary endpoint when survival-improvement endpoints are not feasible, while also emphasizing that survival-related outcomes remain important to assess. The recommendations address how to balance feasibility with evaluation of efficacy and safety.
The document also responds to practical issues in trial conduct: patients may be receiving standard therapies that could change during a study, and investigational products can have risks specific to their mechanism. For example, drugs that suppress myocardial hypercontractility, such as myosin inhibitors, may pose a risk of heart failure if left ventricular contractile function is reduced. Trial plans therefore need to consider background treatment and safety monitoring as well as the choice of efficacy measures.
Key Recommendations
Plan for phenotype-specific development. Because oHCM and nHCM differ in pathophysiology and may have different prognoses, the document considers it appropriate to conduct confirmatory studies separately for each phenotype when evaluating a drug intended for both. It also states that dose and administration for confirmatory trials should desirably be determined using dose-response studies or other relevant data for each phenotype. If dosing for one phenotype is based on dose-response studies in the other, the appropriateness of that approach should be sufficiently justified.
Consider multi-regional trials early. Since oHCM and nHCM are rare diseases with limited patient numbers, conducting confirmatory trials solely in Japan may be challenging. Participation in multi-regional clinical trials should be actively considered from early development.
When relying on overseas confirmatory-trial results, plan a justified comparison. The document discusses situations where overseas efficacy data are already available, or an overseas confirmatory trial is ongoing but Japan cannot participate. In such cases, a strategy may be acceptable that includes a domestic trial or a multi-regional trial excluding the countries or regions in the overseas confirmatory trial. The trial would compare and assess similarity of efficacy and safety between Japanese and non-Japanese populations, while referring to the overseas trial results to support evaluation in Japanese patients. The study design should be as consistent as possible with the reference overseas confirmatory trial. If it differs, the reasons for the differences and the justification for comparability despite those differences should be clearly explained.
Account for children in development plans. Because HCM also occurs in pediatric patients, development plans should take pediatric indications into account. It is recommended to formulate a plan that includes clinical trials to explore appropriate pediatric dosage and administration, as well as establishment of pediatric formulations.
Use an appropriate comparative design and control. In general, confirmatory trials should be randomized, double-blind, parallel-group comparative studies with an appropriate control group. They should maintain appropriate standard therapies, such as β-blockers, in accordance with current treatment recommendations described in relevant guidelines, and use placebo as the control. When a therapy with a similar mechanism of action or place in therapy is already available, superiority or non-inferiority of the investigational product to an active comparator may be evaluated. In that situation, the comparator’s appropriateness should be justified in light of the anticipated clinical positioning of the product under development.
Select efficacy endpoints that reflect both feasibility and treatment goals. The document recommends peak oxygen uptake (pVO₂) as the primary efficacy endpoint when survival-improvement endpoints are not feasible. It gives three reasons: exercise tolerance helps determine treatment strategies and assess response; it provides an objective measure of treatment effect; and pVO₂ has been reported to correlate with prognosis in HCM. When exercise tolerance is the primary endpoint, it is important to include endpoints related to survival improvement as secondary endpoints and to confirm that the investigational product does not adversely affect survival outcomes.
Include symptom measures and consider an oHCM biomarker. Improvement in clinical symptoms, including exertional dyspnea and shortness of breath, is also an important treatment objective. It is recommended to include subjective symptom measures such as the Kansas City Cardiomyopathy Questionnaire Clinical Summary Score (KCCQ-CSS) and New York Heart Association (NYHA) functional classification as secondary endpoints, and to evaluate overall efficacy using these results as well. For oHCM, evaluation of the left ventricular outflow tract (LVOT) pressure gradient is considered useful as a biomarker related to therapeutic effect.
Set the evaluation period to fit the product and target population. The evaluation period should be determined appropriately, taking into account the characteristics of the investigational product and the time required for the therapeutic effect to appear in the target population. For drugs expected to be used for long-term management in clinical practice, long-term safety and efficacy should also be appropriately evaluated.
Manage background treatment and mechanism-related risk. Since confirmatory trials are expected to include patients receiving standard treatment, measures should be implemented to minimize the potential impact of changes in standard therapy on efficacy and safety evaluation. One example is enrolling patients for whom changes to the dosage and regimen of standard therapy are unlikely during the study. If standard therapies are discontinued, modified, or added, those changes should be recorded in detail so their potential impact can be assessed. For products that suppress myocardial hypercontractility, the risk of heart failure due to reduced left ventricular contractile function should be carefully considered. Enrollment of patients with left ventricular ejection fraction (LVEF) below the reference range should be avoided or clearly justified with adequate risk-mitigation measures, and regular echocardiographic monitoring should be performed during treatment.
Practical Implications
Interpretation: For sponsors, these considerations point toward early choices about whether the intended population is oHCM, nHCM, or both, and whether the evidence plan can support separate evaluation by phenotype. A multi-regional strategy may help address recruitment constraints, but the document emphasizes planning for how evidence from an overseas confirmatory trial will relate to evaluation in Japanese patients. If a bridging comparison uses a different design from its reference trial, the difference needs an explicit rationale and explanation of why the results remain comparable.
For statisticians and trial designers, endpoint planning is not simply a choice between a feasible measure and a clinically meaningful one. If pVO₂ is used as the primary endpoint because survival-related primary endpoints are not feasible, the design should still include survival-related secondary endpoints. Symptom measures contribute another dimension of efficacy assessment, and LVOT pressure gradient is a useful therapeutic-effect biomarker in oHCM according to the document. The document does not give a particular sample-size method, treatment-effect threshold, or endpoint hierarchy beyond these considerations.
For clinical operations and investigators, stable background therapy can make it easier to interpret the investigational product’s effects. The document gives enrolling patients unlikely to change standard-therapy dosage or regimen during the study as an example of a measure to reduce the impact of such changes. Recording treatment changes in detail is also important, since these changes may affect efficacy and safety outcomes.
For safety and medical-monitoring teams, the mechanism of action should inform the population and monitoring plan. In particular, the document calls attention to reduced contractile function and heart-failure risk for drugs that suppress myocardial hypercontractility, and it discusses avoiding or justifying enrollment of patients with below-reference-range LVEF alongside regular echocardiographic monitoring. For pediatric development teams, the considerations include not only studying dosage and administration but also establishing pediatric formulations.
Technical Details
The document’s technical considerations connect disease phenotype, trial endpoints, and safety evaluation:
oHCM is defined as a phenotype with resting or provoked LVOT pressure gradient of ≥30 mmHg. The document distinguishes it from nHCM and notes that the two may differ in pathophysiology, prognosis, therapeutic response, and safety profile.
The treatment goal is improvement in long-term prognosis. Where survival-improvement endpoints are not feasible as primary endpoints, pVO₂ is recommended as the primary endpoint, with exercise tolerance providing an objective measure and pVO₂ reported to correlate with prognosis.
When exercise tolerance is primary, include survival-improvement endpoints as secondary endpoints and assess whether survival outcomes are adversely affected. Include symptom assessments such as KCCQ-CSS and NYHA functional classification as secondary endpoints; for oHCM, consider LVOT pressure gradient as a biomarker related to therapeutic effect.
Set the evaluation period according to product characteristics and the time needed for effects to emerge. For long-term-use products, appropriately evaluate long-term safety and efficacy. Implement measures to minimize the potential impact of changes in standard therapy during the trial, and record any discontinuation, modification, or addition of standard therapies in detail.
Use dose-response or other relevant data for each phenotype where possible. For a product suppressing myocardial hypercontractility, consider the risk associated with reduced contractile function, the eligibility of patients with below-reference-range LVEF, risk mitigation, and regular echocardiographic monitoring.
In practical terms, pVO₂ is a measure of peak oxygen uptake during exercise testing and is used here as an indicator of exercise tolerance. LVOT pressure gradient measures the pressure difference associated with obstruction to blood leaving the left ventricle; the document notes its role in assessing oHCM severity and guiding treatment decisions, as well as reported associations with prognosis and exercise tolerance. These measures serve different purposes: pVO₂ may be a primary efficacy endpoint when survival-related primary outcomes are not feasible, while LVOT pressure gradient is described as a useful oHCM biomarker.
Who Should Read It
This document is relevant to sponsors and development teams planning HCM drug programs, particularly those developing treatments for one or both HCM phenotypes. Clinical pharmacologists, statisticians, and trial designers may find its considerations useful when planning confirmatory designs, comparators, endpoint sets, evaluation periods, and phenotype-specific dose selection. Clinical operations teams and investigators may use it to understand the considerations around standard therapy, treatment changes, eligibility, and echocardiographic monitoring. Regulatory affairs professionals may find the discussion of multi-regional development and comparison with overseas confirmatory-trial results relevant to planning development in Japan. It is also pertinent to teams considering pediatric indications and formulations.
Official PMDA Source
- Official title: Consideration in the development of drugs for hypertrophic cardiomyopathy (Early Consideration)
- Issuing body: Pharmaceuticals and Medical Devices Agency (PMDA), Office of New Drug II
- Date on cover: January 27, 2026
- Official PMDA PDF: View the PMDA PDF
- PMDA Early Consideration list page: View the PMDA list page
Source: Pharmaceuticals and Medical Devices Agency (PMDA) website, PMDA list page. This page was created by editing and summarising the PMDA document.
Consult the official document; this summary does not replace it. PMDA provides the English version for reference purposes, and the Japanese original prevails if the two differ. PMDA describes Early Consideration documents as reference information reflecting the Agency’s views at the time of publication; those views may change as scientific knowledge develops.
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Key Takeaways
- PMDA’s considerations address development of drugs for both oHCM and nHCM, which differ in pathophysiology and may have different prognoses.
- Because patient numbers are limited, multi-regional trials should be actively considered from early development.
- Confirmatory trials are generally described as randomized, double-blind, parallel-group comparisons with an appropriate control and maintained standard therapy.
- When survival-improvement endpoints are not feasible as primary endpoints, pVO₂ is recommended as primary; survival-related outcomes and symptom measures remain important secondary assessments.
- Trial plans should address evaluation duration, changes in standard therapies, phenotype-specific dosing, pediatric development, and risks linked to the product’s mechanism.