Cardiac myosin inhibitor
Symptomatic New York Heart Association Class II-III obstructive hypertrophic cardiomyopathy (HCM)
Approved in the US
Camzyos™ (mavacamten) is the first cardiac myosin inhibitor approved by the US Food and Drug Administration (FDA) for the treatment of adults with symptomatic obstructive hypertrophic cardiomyopathy (HCM).
The drug was developed by US-based biopharmaceutical company Bristol-Myers Squibb (BMS) and is distributed by its wholly-owned subsidiary, MyoKardia.
Camzyos is available in 2.5mg, 5mg, 10mg and 15mg capsules, with different coloured caps denoting different strengths of the drug.
The medicine is distributed exclusively through a restricted programme under a risk evaluation and mitigation strategy (REMS), called the Camzyos REMS PROGRAM, due to the potential risk of heart failure it poses.
REMS is a drug safety programme mandated by the FDA to manage potential serious safety concerns associated with certain medications.
Approvals for Camzyos
In March 2021, the FDA accepted BMS’ new drug application for mavacamten. The agency approved the use of Camzyos for treating patients with symptomatic New York Heart Association (NYHA) class II-III obstructive HCM in April 2022.
Camzyos is the first and only FDA-approved cardiac myosin inhibitor that targets the underlying pathophysiology of obstructive HCM.
The drug has also received breakthrough therapy designation from the Chinese regulatory authorities for the treatment of obstructive HCM.
Causes and symptoms of HCM
HCM is a chronic and progressive disease that causes abnormal cell structure and the thickening of the heart muscle, which results in reduced blood flow to body parts. It is characterised by excessive contraction of the heart muscle and reduced functioning of the left ventricle.
In obstructive HCM, the walls of the heart become so rigid and stiff that the blood flow through the heart is blocked.
HCM is prevalent in one in every 500 people worldwide and is mainly caused by mutations in genes encoding muscle proteins of the sarcomere.
Patients with HCM experience fatigue or shortness of breath following exertion, which limits their ability to carry out daily life activities. The condition can also lead to increased risk of atrial fibrillation, stroke, heart failure and sudden cardiac death.
The NYHA classifies four categories of HCM based on the extent of heart failure and the patient’s limitations in physical activity.
Patients classified under class I do not show symptoms and can perform ordinary physical activities such as walking and climbing stairs without any limitation.
Class II patients experience mild symptoms such as mild shortness of breath and/or angina pain and slight limitation during ordinary activities in daily life.
Class III patients witness limitations to normal activities such as walking short distances of up to 100m. Such patients feel comfortable only when at rest.
Class IV patients have severe limitations and complain of symptoms even while resting.
Camzyos’ mechanism of action
Camzyos is an allosteric and reversible inhibitor that controls the cross-bridge formation of myosin and actin proteins by regulating the number of myosin heads that get attached to actin. The therapy works by moving the myosins to an energy-sparing, super-relaxed state.
The inhibition of myosins reduces dynamic left ventricular outflow tract (LVOT) obstruction and increases left ventricular filling pressures.
Clinical trials on Camzyos
The FDA’s approval of Camzyos (mavacamten) was based on data from the Phase III trial EXPLORER-HCM, which was a placebo-controlled, multi-centre, double-blind, randomised parallel group study.
The clinical study confirmed a significant improvement in patients treated with mavacamten compared with those given placebo.
A total of 251 class II and III obstructive HCM patients participated in the study, 123 of whom were administered Camzyos daily while the others received placebo. Participants were randomised to receive an initial dose of 5mg of Camzyos or placebo once a day for a duration of 30 weeks.
The study’s primary endpoint, evaluated at the end of week 30, was an improvement in peak oxygen consumption (pVO2) by at least 1.5ml/kg/min. Around 37% of the patients treated with Camzyos and 17% of the placebo group met this primary endpoint.
The secondary endpoints compared the patients’ response in the two arms of EXPLORER-HCM clinical trial in metrics such as post-exercise LVOT peak gradient, pVO2 change, and the proportion of patients showing an improvement in NYHA class.
Other secondary endpoints included Hypertrophic Cardiomyopathy Symptom Questionnaire Shortness of Breath (HCMSQ-SoB) domain score and Kansas City Cardiomyopathy Questionnaire-23 (KCCQ-23) clinical summary score (CSS).
The two treatment arms were assessed by comparing changes in the metrics from the baseline to week 30.
At least 5% of the patients witnessed adverse reactions during the trial. Dizziness and fainting (syncope) were the most common side effects observed in the participants. Around 27% and 6% of the patients treated with Camzyos complained of dizziness and syncope respectively, while 18% and 6% of those in the placebo group reported the same.