FDA’s Camzyos Teen Label Requires CYP2C19 Testing

CamzyosWhat to know

30-second read

For Cardiology · Pediatrics · Cardiothoracic Surgery

Who

Adolescents aged 12 to under 18, weighing at least 30 kg (66 lb), with symptomatic obstructive HCM — not younger or lighter patients within that age band.

What’s new

FDA expanded Camzyos (mavacamten) to adolescents on 30 September 2026 — the only FDA-approved drug therapy for pediatric obstructive HCM.

Evidence

SCOUT-HCM: 44 adolescents, randomized, placebo-controlled. Valsalva LVOT gradient fell ∼48 mmHg more than placebo at week 28 (P<.0001); no LVEF fell below 50%.

Big advantage

A first non-surgical option for teens whose obstruction isn’t controlled by beta-blockers or disopyramide, without moving straight to septal reduction surgery.

Key consideration

CYP2C19 genotyping is required before the first dose — poor metabolizers need a lower starting and maximum dose; REMS echo monitoring applies at every titration step.

Availability

Approved 30 Sept 2026; dispensed only through REMS-certified specialty pharmacies. List price and payer coverage for the adolescent indication are not yet public.

Practice impactRefer earlier

Practices without REMS-certified dispensing and serial pediatric echocardiography should refer symptomatic adolescents with obstructive HCM to a center that can genotype, dose and monitor Camzyos, rather than manage the first prescription themselves.

Read the full physician analysis

Full analysis · 9 min readFDA label update · CAMZYOS prescribing information · SCOUT-HCM (Pharmacy Times, HCPLive, October 2026)

FDA's 30 September 2026 expansion of Camzyos (mavacamten) to adolescents with symptomatic obstructive hypertrophic cardiomyopathy made news as the first pediatric drug therapy for the disease, built on SCOUT-HCM's 44-patient placebo-controlled trial. The detail that determines whether a practice can actually write the first prescription is further down the label: CYP2C19 metabolizer status must be known, or assumed worst-case, before that first dose — a genetic test most general cardiology and pediatric practices do not routinely order.

A narrower population than the headline suggests

The label sets a weight floor — 30 kg, about 66 pounds — inside the 12-to-17 age band, which in practice excludes some smaller or younger adolescents who otherwise fit the diagnosis. SCOUT-HCM, the trial behind the expansion, was a randomized, double-blind, placebo-controlled Phase 3 study in 44 adolescents with obstructive HCM; at week 28, the least-squares mean reduction in Valsalva left ventricular outflow tract gradient favored mavacamten by roughly 48 mmHg over placebo (P<.0001), and no patient's ejection fraction fell below 50%, the threshold that triggers the drug's core safety concern. This is a real, statistically clean result in a genetically and clinically heterogeneous pediatric HCM population — but a 44-patient trial is also a small one, and it does not by itself identify which specific adolescents gain the most.

The test the headline left out

Mavacamten is metabolized primarily through CYP2C19. Patients who are CYP2C19 poor metabolizers — carrying two loss-of-function alleles — can have roughly three times the drug exposure of normal metabolizers at a standard dose, which raises their risk of the drug's core safety concern: systolic dysfunction. The label's response is specific and mandatory: genotype the patient for CYP2C19 before the first dose, and if treatment must start before results return, dose as a poor metabolizer — a lower starting dose and a lower maximum dose — until the genotype is known. In adults, that means a starting and maximum dose of 2.5 mg and 5 mg respectively for poor metabolizers, against higher tiers for normal, intermediate or rapid metabolizers; the adolescent expansion adds a new 1 mg step specifically so pediatric dosing can follow the same logic at a smaller scale.

This is not boilerplate pharmacogenomic language that practices can skim past. A CYP2C19 genotype test has turnaround time, and a clinic that has never ordered one for a cardiology indication — it's far more familiar in psychiatry and gastroenterology, for clopidogrel and some antidepressants — needs a working relationship with a lab that runs it, a plan for the poor-metabolizer dosing pathway if treatment can't wait, and someone responsible for checking the result before it defaults to the standard dose by inertia.

What the REMS program adds on top

Camzyos carries a boxed warning for heart failure due to systolic dysfunction and is available only through the CAMZYOS REMS program. In adults, the monitoring schedule calls for echocardiographic assessment of LVOT gradient and ejection fraction at weeks 4, 8 and 12 after starting or changing dose, then every 12 weeks during maintenance — reduced to every 6 months only for patients who reach a stable, low-gradient maintenance dose. Every dose change or treatment interruption restarts closer monitoring. None of that changes for adolescents; if anything it is harder to deliver, since pediatric echocardiography capacity and REMS-certified specialty-pharmacy dispensing are not evenly distributed, and a 13-year-old on a titration schedule needs a caregiver who can get them to an echo lab on a fixed cadence for at least the first three months.

Where surgery still has the stronger evidence

Septal reduction surgery — principally surgical myectomy, with alcohol septal ablation generally reserved for older patients where myectomy is not an option — has long been the standard for children and adolescents with severe, drug-refractory left ventricular outflow tract obstruction, conventionally defined as a resting or provoked gradient above 30 mmHg. It is also an outcome where experience matters in a measurable way: surgical literature on HCM myectomy divides surgeons into lower- and higher-volume groups, with higher-volume operators showing less residual obstruction postoperatively. Mayo Clinic, one of the highest-volume HCM surgical programs, reports a pediatric myectomy experience exceeding 200 procedures within an overall program of roughly 4,500. SCOUT-HCM enrolled adolescents with symptomatic obstructive HCM broadly, not specifically the severe, surgery-eligible subset, so Camzyos's approval does not unseat myectomy where myectomy is already indicated — it adds a medical option earlier in the pathway, for patients whose obstruction and symptoms have not yet crossed into clearly surgical territory, or for families who want to defer an open-heart operation while that decision is made.

What changes in a general cardiology or pediatrics practice

• Recognize the referral trigger. A symptomatic adolescent with obstructive HCM not controlled on a beta-blocker or disopyramide is now a candidate for a medical option beyond those two drug classes — a reason to refer to a center that can genotype, dose and monitor Camzyos, not a reason to start it without that infrastructure.
• Know the surgical threshold. A resting or provoked gradient above roughly 30 mmHg with drug-refractory symptoms still points toward surgical evaluation at a high-volume pediatric HCM program, in parallel with or instead of a Camzyos referral, not after it fails.
• CYP2C19 testing is a workflow decision, not a footnote. Identify a lab, define the poor-metabolizer dosing pathway for cases that can't wait on results, and assign ownership of confirming the result before the standard dose becomes the default.
• REMS logistics belong in the referral conversation. Families should understand the echo cadence — roughly monthly for the first three months — before starting, not after the first missed appointment.
• Transition planning starts now. An adolescent stabilized on Camzyos will become an adult Camzyos patient; the handoff from pediatric to adult cardiology, and from a pediatric to an adult REMS-certified pharmacy, is a planning problem this approval creates, not one it solves.

The approval itself is straightforward news: a first pediatric drug option where there was none. What actually determines whether an individual adolescent gets it safely and on schedule is the genotyping and monitoring infrastructure sitting underneath that headline — infrastructure a referral, not a prescription pad, is usually the right first step toward. Every story on this desk is filed by specialty on the For Physicians front.

Frequently asked questions

Can a general cardiologist or pediatrician prescribe Camzyos to an adolescent?

The label doesn't restrict prescribing by specialty, but the REMS program's echocardiographic monitoring schedule and the requirement to act on CYP2C19 genotype results before the first dose mean most practices without pediatric echo capability and REMS-certified dispensing will refer rather than initiate therapy themselves.

What happens if a teenager starts Camzyos before CYP2C19 results come back?

The label's approach (consistent with the adult indication) is to dose as if the patient is a CYP2C19 poor metabolizer — the lower starting and maximum dose — until the genotype is known, then adjust. Starting at the standard dose before genotyping is not the labeled approach.

Does this approval replace septal myectomy for adolescents with severe obstruction?

No. SCOUT-HCM enrolled adolescents with symptomatic obstructive HCM broadly, not specifically those with severe, refractory obstruction who are myectomy candidates. Surgical myectomy remains the standard for severe, drug-refractory obstruction, ideally at a high-volume pediatric HCM center; Camzyos adds a medical option earlier in that pathway, not a replacement for surgery when surgery is already indicated.