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FDA Expands Camzyos Approval: A New Option for Children Weighing at Least 30 Kilograms With Obstructive Hypertrophic Cardiomyopathy
A trial involving 44 adolescents has brought a drug originally used in adults to regulate heart muscle contraction into pediatric care. The study showed reduced obstruction to blood flow out of the heart, but long-term benefits and safety require further follow-up, and the heart failure warning and treatment monitoring requirements remain in place.
For children with obstructive hypertrophic cardiomyopathy, thickening of the heart muscle can narrow the passage through which blood leaves the heart, limiting daily activities because of breathlessness and fatigue. On September 30, the U.S. Food and Drug Administration (FDA) expanded approval of Camzyos (mavacamten) to include symptomatic pediatric patients weighing at least 30 kilograms, making it the first FDA-approved treatment to improve exercise capacity and symptoms in this group.
This disease, which is often linked to inherited factors, obstructs the left ventricular outflow tract. Mavacamten is a cardiac myosin inhibitor that reduces excessively strong heart muscle contractions to relieve the obstruction to blood flow out of the heart. It was first approved for adults in 2022; this approval extends the treatment option to pediatric patients who meet the weight requirement.
The Phase 3 SCOUT-HCM trial supporting the approval enrolled 44 patients aged 12 to under 18 years with New York Heart Association functional class II–III symptoms. The randomized, double-blind study compared treatment outcomes over 28 weeks, with 23 participants receiving mavacamten and 21 receiving placebo. The scope of approval is defined by weight, while the trial’s direct evidence comes primarily from adolescents.
The primary endpoint was the change in the left ventricular outflow tract pressure gradient during the Valsalva maneuver, in which patients hold their breath and strain. This measurement reflects the degree of obstruction. According to data released by Bristol Myers Squibb (BMS), at week 28, the adjusted mean difference between the drug and placebo groups was a reduction of 48.0 millimeters of mercury, with a 95% confidence interval ranging from a reduction of 67.7 to 28.3 millimeters of mercury, reaching statistical significance.
An improvement in the pressure gradient does not mean that all long-term clinical questions have been answered. The FDA noted that, in adult studies, reduced obstruction was accompanied by improvements in exercise capacity and symptoms. Combined with the pediatric trial results, this suggests that eligible children are also expected to benefit. However, this limited-size study, with a 28-week controlled period, is not sufficient to establish an effect on reducing the risk of heart failure, fatal arrhythmias, or death.
Regarding safety, BMS said that no patient’s left ventricular ejection fraction fell below 50% during the trial, and no adverse events led to treatment discontinuation; two participants in each group experienced serious adverse events. Ejection fraction reflects the proportion of blood the heart pumps out with each contraction. However, the absence of a marked decline in a small trial does not rule out rarer risks or those associated with long-term use.
Reducing contractile force is also why this drug requires careful management: an excessive effect could weaken the heart’s ability to pump blood. Camzyos retains its boxed warning for the risk of heart failure. Heart function must be assessed by echocardiography before and during treatment, and distribution is restricted through a Risk Evaluation and Mitigation Strategy (REMS). This expanded approval provides a new treatment option while making continued monitoring an important requirement for pediatric use.