The Food and Drug Administration on Sept. 30 approved Bristol Myers Squibb’s heart drug Camzyos, also called mavacamten, for pediatric patients with symptomatic obstructive hypertrophic cardiomyopathy who weigh at least 30 kilograms, or 66 pounds. It is the first drug approved for children with the condition, the company said in its announcement.
The approval extends a drug that has been available to adults since 2022. Bristol Myers Squibb said more than 25,000 U.S. patients have taken it since then.
What the Camzyos pediatric approval covers
Obstructive hypertrophic cardiomyopathy, or oHCM, is a form of a genetic heart disease in which the heart muscle thickens and blocks blood flow out of the left ventricle. The American Heart Association estimates that 1 in 500 people have some form of HCM, and says many cases go undiagnosed. The association calls the condition the leading cause of sudden cardiac death in young athletes.
The label wording matters. The FDA’s indication, as quoted in the company’s release, covers “adults and pediatric patients weighing 30 kg (66 lbs) or more.” It sets a weight floor, not an age floor. The trial that supported the approval enrolled only adolescents ages 12 to younger than 18.
The label therefore reaches down to any child who weighs 66 pounds or more, including children younger than the youngest people studied. The company’s release does not say how many such children there are.
The drug is dosed by weight, according to HCPLive. Patients who weigh 35 kilograms to less than 45 kilograms start at 2.5 milligrams once a day, and those who weigh 45 kilograms or more start at 5 milligrams. Doctors adjust the dose using echocardiograms.
What the SCOUT-HCM trial found
The evidence comes from SCOUT-HCM, a randomized, double-blind, placebo-controlled trial of 44 adolescents with symptoms rated as class II or III on the New York Heart Association scale. Twenty-three received Camzyos and 21 received a placebo. Healio reported that the results were presented March 29 at the American College of Cardiology’s annual meeting in New Orleans and published the same day in the New England Journal of Medicine.
The main measure was the pressure gradient across the heart’s outflow tract when a patient strains, a marker of how hard the heart pumps against the blockage. After 28 weeks, the company said the gradient fell by 48 millimeters of mercury more in the Camzyos group than in the placebo group, a difference with a p-value below 0.0001. Healio reported that the average gradient in treated patients fell from 78.4 to 29 millimeters of mercury.
Sources differ on the figures for each group. Bristol Myers Squibb’s release gives a drop of 49.4 millimeters of mercury on Camzyos and 1.8 on placebo. Contemporary Pediatrics reported 48.5 and 0.5. Both outlets put the difference between the groups at 48 millimeters of mercury.
Secondary measures also moved. HCPLive reported that resting and post-exercise gradients improved and that left ventricular wall thickness fell by 1.8 millimeters in treated patients. Healio reported better diastolic function, which describes how well the heart relaxes and fills, and improvement in New York Heart Association class, the scale doctors use to grade symptoms. About 30% of the participants were female, Healio said.
On safety, no patient’s ejection fraction, the share of blood the heart pumps out with each beat, fell below 50%. Serious adverse events occurred in two patients on Camzyos (9%) and two on placebo (10%), and no one stopped treatment because of side effects, the company said. Healio reported that no one died, and HCPLive reported no cases of atrial fibrillation or heart failure during the trial.
Limits of the trial and the safety program
The study is small. Its 44 patients are about 0.2% of the 25,000 adults the company says have taken the drug. Healio listed other limits: the group was predominantly white, at 68%, it excluded younger children and some genetic conditions, and a long-term extension study is still running.
Joseph Rossano, chief of cardiology at Children’s Hospital of Philadelphia, said at the March presentation that “there are no approved therapies for pediatric patients” with the disease, according to Healio.
Contemporary Pediatrics reported that before this approval, adolescents who needed treatment received beta-blockers or calcium-channel blockers, which ease symptoms without targeting the disease mechanism. Patients who stayed symptomatic often needed surgery to remove or shrink part of the thickened heart wall.
In an interview with Pharmacy Times, Rossano said the adolescent results matched or exceeded those of EXPLORER-HCM, the adult trial that led to the 2022 approval. That outlet described the trial as enrolling 43 adolescents, while the company and Healio count 44. Rossano also described open questions in Contemporary Pediatrics.
They include whether benefits last past 28 weeks, how the drug affects the heart’s pumping and rhythm over years, whether it should be a first treatment, and whether it can delay or prevent surgery.
The drug carries a boxed warning, the FDA’s strongest, that it reduces the ejection fraction and can cause heart failure. Starting it is contraindicated when ejection fraction is below 55%, according to the company’s release. It is available only through the Camzyos REMS program, a restricted-distribution system that requires doctors to be certified, patients to be enrolled and pharmacies to be certified. Patients need echocardiograms before and during treatment.
How quickly the FDA acted
Contemporary Pediatrics reported that the FDA granted the application priority review and set a target decision date of Sept. 30. The agency approved it on that date. Bristol Myers Squibb said in the earlier release that the pediatric group has a high unmet medical need, according to the same outlet.
The company’s release does not give a price for pediatric patients. Eligibility turns on the 66- pound weight limit and on enrollment in the REMS program.
