Aficamten vs Mavacamten: Two Cardiac Myosin Inhibitors Compared

Aficamten and mavacamten are both cardiac myosin inhibitors used in obstructive hypertrophic cardiomyopathy, but they differ in half-life, dosing, and regulatory status. Mavacamten was FDA-approved in April 2022 and carries a boxed warning for systolic dysfunction; aficamten was FDA-approved in December 2025 with a 3 to 4 day half-life that reaches steady state in about a week. Neither drug cures the disease. Both reduce left ventricular outflow tract obstruction by roughly 30 to 50 percent in responders. The practical difference is monitoring burden, drug-interaction risk, and titration speed, not a proven gap in survival.

How both drugs quiet an over-contracting heart

The shared target is the sarcomere, the contractile unit inside every heart muscle cell. In hypertrophic cardiomyopathy, a mutation in genes such as MYH7 or MYBPC3 makes myosin heads bind actin too readily. The result is hypercontractility, a thickened septum, and dynamic obstruction of the left ventricular outflow tract.

Cardiac myosin inhibitors bind the myosin motor domain and shift it into a super-relaxed state. Fewer heads are available to pull on actin at any moment, so systolic force drops modestly and the outflow gradient falls. In plain terms: the drug turns down the volume of each heartbeat without stopping the beat.

The distinction between the two molecules is pharmacokinetic, not pharmacodynamic. Both are selective myosin ATPase inhibitors. Aficamten was engineered with a shorter half-life and a steadier exposure profile to make titration less risky. Mavacamten has a longer half-life and is metabolized mainly by CYP2C19, which creates interaction and variability problems.

The head-to-head numbers that matter

The table below summarizes the parameters a clinician actually weighs. Values reflect FDA labeling and the pivotal trial data as of late 2026.

The half-life gap is the single most consequential difference. A drug that clears in 3 to 4 days can be withdrawn and wash out within roughly two weeks. Mavacamten can take a month or longer to fully clear, which matters if a patient develops systolic dysfunction.

Trial evidence: what each pivotal study actually showed

EXPLORER-HCM enrolled 251 patients with obstructive hypertrophic cardiomyopathy and randomized them to mavacamten or placebo for 30 weeks. The primary endpoint combined gradient reduction and functional improvement. Roughly 37 percent of mavacamten patients met the composite versus 17 percent on placebo. Mean resting outflow gradient fell by about 35 to 40 mmHg in the treatment arm.

SEQUOIA-HCM tested aficamten in 282 patients over 24 weeks. The primary endpoint was change in peak oxygen uptake during cardiopulmonary exercise testing. Aficamten improved peak VO2 by about 1.7 mL/kg/min versus placebo, and reduced the provoked gradient by roughly 40 mmHg. These are different endpoints, so a direct efficacy comparison is not clean. Neither trial was powered to detect a mortality difference.

A non-obvious caveat: the two trials used different exercise protocols, different follow-up windows, and different composite definitions. Any claim that one drug is "more effective" than the other outruns the evidence. What the data support is that both produce clinically meaningful gradient reduction in a majority of obstructive patients.

Dosing, titration, and the monitoring burden

Mavacamten titration is slow. Patients start at 5 mg daily and typically wait 4 weeks before the next echo and dose adjustment. The label permits increases to 10 mg and then 15 mg, with echocardiography at each step. Because CYP2C19 poor metabolizers clear the drug slowly, genotype and concomitant drug review are mandatory.

Aficamten titration is faster because steady state arrives in about a week. Dose steps run from 5 mg to 10 mg, 15 mg, and up to 20 mg, with echo checks between steps. The compressed schedule means patients reach a therapeutic dose in weeks rather than months.

Both drugs sit inside a Risk Evaluation and Mitigation Strategy program. That means prescriber certification, pharmacy certification, and patient enrollment before the first dose. In plain terms: you cannot simply write the prescription and walk away; the system gates access by design.

Monitoring thresholds are reconciled as follows: a left ventricular ejection fraction below 50 percent triggers dose interruption for both agents, and any drop of more than 10 percentage points from baseline warrants the same pause, regardless of the absolute number.

Drug interactions and the CYP2C19 problem

Mavacamten's dependence on CYP2C19 is its Achilles heel. Strong CYP2C19 inhibitors such as omeprazole or fluconazole can raise exposure several-fold. Strong CYP3A4 inhibitors add further risk. The label lists a long roster of prohibited or dose-adjusted combinations, and every new prescription, including common antibiotics, requires a check.

Aficamten leans mainly on CYP3A4, so the interaction list is shorter but not empty. Strong CYP3A4 inhibitors still require dose reduction. The practical effect is that aficamten leaves more room for ordinary primary-care prescribing without a pharmacy consult.

This is where the two drugs diverge most in real-world use. A patient on mavacamten who develops a urinary tract infection and needs an azole antifungal may face a dose hold. The same patient on aficamten faces a smaller adjustment. Neither is interaction-free.

Who should not take either drug

Red-flag warnings are absolute and worth listing plainly:

• Pregnancy: both drugs cause fetal harm in animal studies and are contraindicated in pregnancy.
• Severe hepatic impairment: avoid both; exposure rises unpredictably.
• Concurrent strong CYP2C19 or CYP3A4 inhibitors with mavacamten: contraindicated without dose adjustment.
• Left ventricular ejection fraction below 50 percent at baseline: do not start.
• Known hypersensitivity to the drug or its excipients: do not use.
• Patients unable to commit to REMS echo monitoring: defer treatment.

Common misconceptions corrected

The most persistent myth is that these drugs replace septal reduction therapy. They do not. Myectomy and alcohol septal ablation remain definitive options for anatomically suitable patients with refractory symptoms. Myosin inhibitors are for symptomatic obstructive disease in patients who can tolerate long-term monitoring.

A second misconception is that a lower gradient means a cured heart. The hypertrophy and fibrosis of hypertrophic cardiomyopathy persist. The drugs reduce obstruction and improve symptoms; they do not reverse the underlying genotype.

A third is that aficamten is simply "mavacamten 2.0." The shorter half-life is a genuine safety advantage in titration, but it also means missed doses cause faster loss of effect. Adherence matters more, not less.

What to actually do if you or a patient is choosing

Start by confirming the diagnosis with echocardiography showing a resting or provoked gradient of 30 mmHg or more, or 50 mmHg or more for the classic obstructive phenotype. Then verify ejection fraction is at least 50 percent.

Review the full medication list against the interaction tables before the first dose. Genotype testing for CYP2C19 is reasonable for mavacamten candidates and unnecessary for aficamten.

Set the echo schedule at the outset. For mavacamten, plan visits at roughly 4-week intervals during titration. For aficamten, plan visits at 2 to 4 week intervals given the faster steady state.

Discuss the trade-off explicitly: faster titration and fewer interactions with aficamten, versus two additional years of post-marketing safety data and broader insurer familiarity with mavacamten.

Limitations of the current evidence

No head-to-head randomized trial has compared aficamten and mavacamten directly. All comparisons rest on separate trials with different endpoints. Long-term outcome data beyond roughly two years are limited for both agents, and aficamten's post-marketing surveillance window is still short.

Cost and access remain unresolved variables. Both drugs are specialty-tier medications with list prices in the tens of thousands of USD annually before insurance. Prior authorization is routine.

The field is moving quickly. Newer myosin inhibitors and gene-based approaches are in early trials, and the relative position of these two drugs will shift as that evidence matures. For now, the choice hinges on pharmacokinetics, monitoring logistics, and interaction profile rather than a demonstrated difference in hard outcomes.