Mavacamten Shows Landmark Success in Adolescent Obstructive HCM

New data presented at the American College of Cardiology’s Annual Scientific Session (ACC.26) and simultaneously published in the New England Journal of Medicine have signaled a potential paradigm shift for the treatment of pediatric patients with obstructive hypertrophic cardiomyopathy (oHCM). Results from the phase 3 SCOUT-HCM (NCT06253221) trial demonstrate that mavacamten (Camzyos; Bristol Myers Squibb), a first-in-class cardiac myosin inhibitor, significantly reduces blood flow obstruction and improves cardiac biomarkers in symptomatic adolescents, marking the first time this therapy has been clinically assessed in a cohort under the age of 18 years.¹

A Critical Unmet Need

HCM is the most common inherited cardiovascular disease, and although it affects all ages, pediatric-onset HCM is associated with a notably worse prognosis than adult-onset forms. Children diagnosed with the condition face a greater risk of life-threatening arrhythmias and nearly double the risk of requiring a heart transplant or experiencing sudden cardiac death.²

Despite these high stakes, the FDA and European Medicines Agency have historically lacked approved pharmacologic therapies for pediatric oHCM. Current management typically involves off-label use of β-blockers, calcium-channel blockers, or disopyramide—treatments that provide symptomatic relief but do not address the underlying pathophysiology of hypercontractility. Consequently, many pediatric patients are eventually referred for invasive surgical myectomy to relieve obstruction.²

The SCOUT-HCM Trial: Breaking New Ground

The SCOUT-HCM trial was a double-blind, randomized, placebo-controlled study involving 44 symptomatic adolescents (12 to < 18 years) with New York Heart Association class II or III oHCM. The primary objective was to evaluate the change in the Valsalva left ventricular outflow tract (LVOT) pressure gradient from baseline to week 28.^1,3,4

The results were striking. At week 28, the mavacamten group experienced a least-squares mean change in the Valsalva LVOT gradient of −48.5 mm Hg, compared with a negligible change of −0.5 mm Hg in the placebo group. This represented a significant treatment difference of −48.0 mm Hg (P < .001). Furthermore, the therapy successfully reduced gradients to below the guideline-based diagnostic threshold for obstruction (30 mm Hg) in 65.2% of patients treated with mavacamten compared with just 4.8% in the placebo arm.^3,4

Clinical Relevance for Pharmacists: Dosing and Monitoring

For pharmacists, the SCOUT-HCM data provide a vital blueprint for the potential clinical management of this complex patient population. Unlike static dosing regimens, mavacamten requires a highly individualized approach based on body weight and echocardiographic feedback.

Therapy was initiated at 5 mg once daily for patients weighing 45 kg, and 2.5 mg once daily for those between 35 kg and 45 kg. The trial used a dosing range of 1 mg to 15 mg. Dose adjustments occurred at predefined intervals: potential down-titration at weeks 5 and 9, and potential uptitration at weeks 12 and 24, based on the Valsalva LVOT gradient and left ventricular ejection fraction (LVEF).

Pharmacists should note that 83% of the mavacamten group remained on background β-blocker therapy during the trial, suggesting mavacamten will likely serve as an add-on targeted therapy rather than a total replacement for the existing standard of care.

Beyond Obstruction: Structural and Biomarker Improvements

The relevance for clinical pharmacists extends to the monitoring of disease progression markers. Mavacamten showed a favorable signal for cardiac remodeling. Secondary end points revealed significant reductions in maximal left ventricular wall thickness (a difference of −1.8 mm vs placebo) and improvements in the E/e′ ratio, a measure of diastolic function.³

Perhaps most importantly for a long-term outlook, mavacamten led to a dramatic reduction in biomarkers of cardiac stress and myocardial injury. N-terminal pro-B-type natriuretic peptide levels in the mavacamten group were reduced to a ratio of 0.23 compared with placebo at week 28, and similar favorable trends were observed for high-sensitivity cardiac troponin I and T. As these markers are associated with heart failure progression and death, these findings suggest that early intervention in adolescence could potentially alter the natural history of the disease.³

Safety and the Pharmacist’s Vigilance

The safety profile of mavacamten in adolescents mirrored that seen in adult trials, with no new safety signals identified. Adverse events were similar between groups (78% for mavacamten vs 81% for placebo).^1,3,4

A critical safety parameter for pharmacists to monitor is the LVEF. Because mavacamten reduces the heart’s squeezing strength by inhibiting myosin, there is a risk of systolic dysfunction. However, in the SCOUT-HCM trial, no patient experienced a reduction in LVEF to less than 50%, and no deaths occurred during the study. Pharmacists will likely play a central role in ensuring that the frequent echocardiographic monitoring required for this drug is strictly followed to prevent oversuppression of cardiac contractility.^3,4

Conclusion

Although the trial was limited by a relatively small, predominantly White sample size and a short 28-week duration, its success offers the first robust evidence for targeted pharmacologic intervention in adolescent oHCM. Joseph Rossano, MD, MS, FAAP, FACC, the study’s lead author, noted that starting children on this therapy at a young age might prevent decades of ongoing injury. As the long-term extension of SCOUT-HCM continues, pharmacists must prepare for a future where they are the stewards of this high-touch, precision-medicine approach to pediatric heart health.

REFERENCES

1. Rossano JW, Canter CE III, Wolf C, et al. Mavacamten in symptomatic adolescent patients with obstructive hypertrophic cardiomyopathy: results from the phase 3 SCOUT-HCM trial. Presented at: American College of Cardiology 2026 Scientific Sessions. March 28-30, 2026; New Orleans, LA.

2. Colan SD. Hypertrophic cardiomyopathy in childhood. Heart Fail Clin. 2011;6(4):433-444. doi:10.1016/j.hfc.2010.05.004

3. Rossano JW, Canter C, Wolf CM, et al. Mavacamten in adolescents with obstructive hypertrophic cardiomyopathy. N Engl J Med. Published online March 29, 2026. doi:10.1056/NEJMoa2601103