Mavacamten

Mavacamten is a selective cardiac myosin inhibitor (new drug class).

Significance: Mavacamten is the first and so far only drug in this new class of active ingredients approved and available in Germany. (Approved in Europe since 2023, approved in the USA since 2022). It is the first substance that enables a causal disease-specific drug treatment of hypertrophic obstructive cardiomyopathy (HOCM) for which previously only symptomatic drug therapy or septal ablation was available.

With the decision of the GB-A, which confirms evidence of a considerable additional benefit compared to the previous symptomatic therapy, therapy with mavacamten has been reimbursable by the SHI since 2024 (practice specialty) and the necessary genotyping for CYP2C19 in a certified special laboratory is also reimbursable.

Mechanism of action: Mavacamten is an allosteric, selective and reversible inhibitor of cardiac myosin. The approval is based on the results of the Phase III studies (Explorer-HCM (Olivotto I et.al. 2020), Valor-HCM (Desai MY et.al. 2021), in which it was shown that mavacamten leads to a clinically relevant reduction in the outflow gradient in the left ventricular outflow tract (LVOT) compared to placebo without a significant reduction in left ventricular pump function. Improved performance, maximum oxygen saturation (V O2 max) and thus improvement of the NYHA stage compared to placebo could be achieved (Desay MY et. al. 2022), (Saberi S et.al. 2021).

The drug has a new mode of action and thus offers a promising new therapeutic option for patients with HOCM(hypertrophic obstructive cardiomyopathy), a rare, mostly genetic disease with changes in the sarcomere (myosin-binding protein C, beta-myosin heavy chains), which is chronically progressive and can already lead to a severe reduction in performance, an increased risk of arrhythmia, sudden cardiac death (SCD) and severely impaired quality of life in people aged between 40-60 years. Until now, only symptom-oriented drug therapies (and in advanced cases septal ablation and surgery) have been available for these patients, but no adequate specific drug therapy options (Braunwald et al. 2023).

Mavacamten is the first approved drug in this class (selective cardiac myosin inhibition) to target the underlying pathophysiology of HOCM (Braunwald et.al.2023).

The drug reduces myocardial contractility by inhibiting the formation of excess myosin-actin cross-bridges, which are causative for hypercontractility, left ventricular hypertrophy, reduced myocardial elasticity and narrowing of the LVOT (Braunwald et. al. 2023). It acts by specifically reducing the activity of cardiac myosin adenosine triphosphatase (myosin ATPase) on the heavy chains of cardiac myosin. The effect is dose-decreasing and reversible (Green et.al. 2016).

Remark: Effects on skeletal muscle cells are not expected, as the mechanism of action is based on a selective effect on cardiac myocytes (Green et.al. 2016).

For an overview of the mechanism of action, the current study situation, critical aspects relevant to treatment and expected future developments, see (Braunwald et.al. 2023).

Mavacamten is administered orally and rapidly absorbed. The time to maximum concentration (Tmax) is 1 to 2 hours. Plasma protein concentration: approx. 97%. Plasma half-life, accumulation (time to steady-state) and elimination are strongly dependent on the metabolization phenotype.

Mavacamten is mainly metabolized via cytochrome oxidase P450 (CYP) in the liver, with metabolism occurring mainly via the enzyme CYP2C19 (approx. 74%) and to a lesser extent via CYP3A4 (18%) and CYP2C9 (8%) (product information Camzyos).

Mavacamten exposure is essentially determined by the genetically determined metabolization rate of CYP2C19. Phenotypically, slow, intermediate, normal, fast and over-fast metabolizers can be distinguished on the basis of genotyping.

The terminal half-life is variable according to the metabolization rate, in so-called 'normal metabolizers' it is approx. 6-9 days and can be extended to up to 23 days in so-called 'slow metabolizers'.

Elimination is 80% (only approx. 3% unchanged) via the kidneys.

Treatment of symptomatic hypertrophic obstructive cardiomyopathy (HOCM) in NYHA stage II-III with EF (ejection fraction) ≥ 55%. (The drug must not be used if the ejection fraction is below 55%). To improve cardiac function and symptoms. The indication, treatment and necessary ongoing therapy monitoring should be carried out by cardiologists with experience in the treatment of patients with cardiomyopathies.

The ESC guidelines from fall 2023 give a class IIa recommendation for treatment with mavacamten if optimal drug therapy with non-vasodilating beta-blockers or calcium channel antagonists (and/or disopyramide) is ineffective (IIa B) or is not tolerated or contraindications exist (IIa A). A recommendation for first-line treatment with mavacamten was not given due to a lack of comparative studies with the currently available first-line drug therapy (Arbelo E et al. 2023).

Mavacamten is embryotoxic and must therefore not be used during pregnancy. Pregnancy must be safely ruled out and reliable contraception must be ensured (hormonal contraception is not safe with mavacamten! see Interactions!).

If you wish to have children, contraception must be continued for up to 6 months after discontinuation of mavacamten to ensure that there is no further exposure! (Camzyos production information)

Mavacamten should not be used during breastfeeding (safety data are not available)!

Dose gradually and according to the result of the genotyping of CYP2C19 to determine the metabolization phenotype. Overdosing can lead to left ventricular dysfunction and heart failure! Danger especially with slow-amplitude metabolization with corresponding genotype. Absolute caution is required here, as left ventricular dysfunction is a serious side effect that can lead to heart failure and death!

Note: Genotyping of CYP2C19 is mandatory for individual dose determination! Based on genotyping, different phenotypes for metabolization can be distinguished (slow, intermediate, normal, fast and over-fast metabolizers). Patients with the CYP2C19 phenotype "slow metabolizers" may have an increased exposure to mavacamten (up to 3-fold), which may lead to an increased risk of systolic dysfunction compared to "normal metabolizers". If treatment is started before the CYP2C19 phenotype is determined, patients should be treated according to the dosing instructions for "slow metabolizers" until the CYP2C19 phenotype is determined (Camzyos product information).

Dosing regimens as well as clinical monitoring, dose maintenance and adjustment according to the different phenotypes can be found in the SmPC for Camzyos (mavacamten) (Camzyos product information).

The titration of the dose is carried out individually according to appropriate schemes and additional clinical monitoring and monitoring of cardiac function by means of echocardiography (EF and LVOT) (Camzyos product information)

In case of overdose or signs of left ventricular dysfunction, the dose must be reduced or completely interrupted until symptoms are reversible. Note the long half-life, which can be 6 - 23 days depending on the different metabolization rates of the phenotypes; additional supportive medical measures may need to be initiated.

Incidence of the CYP2C19 metabolization phenotype "slow metabolizer" is about 2% for Caucasian and about 18% for Asian populations.

The most important and serious adverse effect is left ventricular dysfunction or heart failure in case of overdosage or excessive exposure to mavacampten.

The effect of mavacampten is reversible when the dose is reduced or interrupted. However, the long half-life/elimination time of mavacampten and the possible need for additional supportive medical measures to stabilize the circulation are problematic with regard to the risk. Continuous monitoring of clinical symptoms and medication is therefore essential as a precautionary measure!

Other common adverse effects are also:

Dizziness, syncope, dyspnea

Numerous drugs are also metabolized in the liver via the cytochrome oxidase P450 (CYP) enzyme system, e.g. antibiotics, steroids, antidepressants, antiepileptic drugs, drugs against hypertension and cardiac arrhythmia and many others. As well as some non-prescription drugs, e.g. many phytopharmaceuticals, toxins, but also stimulants and foods.

All these substances can influence the metabolism of mavacamten and thus the exposure and potentially lead to an overdose or reduced effect. This also applies to drugs that are inducers of the CYP enzyme systems when they are discontinued, as this also increases mavacamten exposure!

Conversely, mavacamten can also influence the effect of additional medication, e.g. the effect of hormonal contraception may be reduced and hormonal contraception can no longer be safely guaranteed in this case. Women of childbearing age who are treated with mavacamten must therefore use other safe methods of contraception if possible.

Interactions due to additional medications should be clarified accordingly before administering the medication, see e.g. drugbank.com and require regular monitoring and dose adjustment if necessary.

Simultaneous administration of negative inotropic substances should be avoided if possible, as the negative inotropic effect of mavacamten can be enhanced. Strongly negative inotropic substances are contraindicated (see contraindications).

For further information on interactions, see Camzyos product information.

The drug is only approved for adults.

Not to be used for systolic dysfunction defined as asymptomatic LVEF ≤50%. Echocardiography with determination of EF is mandatory before starting therapy!

There is also an increased risk of systolic dysfunction in patients with serious illnesses, such as infection, cardiac arrhythmias, including atrial fibrillation or uncomplicated tachycardia, or in patients undergoing heart surgery!

Mavacamten must not be used during pregnancy and in women of childbearing potential who are not using reliable contraception.

There is a partial contraindication for concomitant treatment with CYP2C19 inhibitors or CYP3A4 inhibitors (see Camzyos Information for healthcare professionals).

Note: The drug is still subject to increased pharmacovigilance, as long-term data are not yet available!

^Camzyos® 2.5mg 5mg 10mg 15mg

The drug has been approved in Europe since 2023 (approved in the USA since 2022).

Mavacamten is exceptionally expensive and is also associated with additional costs due to the comprehensive monitoring measures.

This once again raises the issue of adequate and guideline-based care for all patients with limited resources in the healthcare system.

The cost-benefit assessment by the Federal Joint Committee was positive and a considerable additional benefit for the care of the patients concerned is confirmed (Federal Joint Committee),(Bergmann MW 2024).

It remains to be seen whether additional new drugs in this new drug class that are already in development and testing will bring about a positive change in the cost situation.

1. Arbelo E et al. 2023 ESC guidelines for the management of cardiomyopathies: developed by the task force on the management of cardiomyopathies of the European Society of Cardiology (ESC). Eur Heart J. 2023;44:3503-3626.
2. Bergmann MW, Hohmann J. Conflict between guidelines and cost-effectiveness? Therapy of HOCM from a medical and legal perspective. Special publication, Deutscher Ärzteverlag, Management Aktuell; 03/24, 1-4 (on behalf of Bristol-Meyers-Squibb).
3. Braunwald E et al. Mavacamten: a first-in-class myosin inhibitor for obstructive hypertrophic cardiomyopathy. Eur Heart J. 2023;44:4622-4633. doi.org/10.1093/eurheartj/ehad637
4. Desai MY et al. Myosin inhibition in patients with obstructive hypertrophic cardiomyopathy referred for septal reduction therapy. J Am Coll Cardiol 2022;80:95-108.
5. Desai MY et al; Study design and rationale of VALOR-HCM: evaluation of mavacamten in adults with symptomatic obstructive hypertrophic cardiomyopathy who are eligible for septal reduction therapy. Am Heart J. 2021;239:80-89.
6. Green EM et al. A small-molecule inhibitor of sarcomere contractility suppresses hypertrophic cardiomyopathy in mice. Science. 2016;351:617-621.
7. Federal Joint Committee; www.g-ba.de/bewertungsverfahren/nutzenbewertung/979/
8. https://go.drugbank.com/categories/DBCAT000403
9. Olivotto I et al; EXPLORER-HCM Study Investigators. Mavacamten for treatment of symptomatic obstructive hypertrophic cardiomyopathy (EXPLORER-HCM): a randomized, double-blind, placebo-controlled, phase 3 trial. Lancet. 2020;396:759-769.
10. Product information Camzyos Bristol Myers Squibb.
11. Saberi S et al. Mavacamten favorably impacts cardiac structure in obstructive hypertrophic cardiomyopathy: EXPLORER-HCM cardiac magnetic resonance substudy analysis. Circulation. 2021;143:606-608.

12. Nag S, Gollapudi SK, Del Rio CL et al (2023). Mavacamten, a precision medicine for hypertrophic cardiomyopathy: From a motor protein to patients. Sci Adv. 9(30):eabo7622. doi: 10.1126/sciadv.abo7622.

Specialist information Red List Mavacamten ^Camzyos®