Cytokinetics has initiated a Phase III clinical trial comparing cardiac myosin inhibitor aficamten to metoprolol as monotherapy for the treatment of symptomatic obstructive hypertrophic cardiomyopathy (HCM).

The active-comparator, double-blind, multi-centre, randomised ‘Metoprolol vs Aficamten in Patients with LVOT Obstruction on Exercise Capacity in HCM’ (MAPLE-HCM) trial intends to enrol 170 patients.

These patients will be randomised into a 1:1 ratio to receive either aficamten or metoprolol, a beta blocker. They will be arranged by CPET exercise modality, including bicycle or treadmill, and recently diagnosed versus chronic obstructive HCM.

They should have resting left ventricular outflow tract gradient (LVOT-G) ≥30mmHg and/or post-Valsalva LVOT-G ≥50mmHg during the first screening.

Prior to the second screening visit, all patients on standard of care (SOC) therapy will undergo a 14-day washout period followed by another seven days with no SOC therapy.

Each participant will be administered four escalating doses of aficamten or metoprolol. A 5mg of aficamten once a day will be given to patients who will also receive an echocardiogram at weeks 2, 4 and 6 to conclude that can they be up-titrated to 10mg, 15mg or 20mg of escalating doses.

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Patients on SOC will receive 50mg once daily and an echocardiogram for the same weeks as the aficamten group to determine that can they receive escalating doses of 100mg, 150mg or 200mg.

Change in peak oxygen uptake (pVO2) from baseline to week 24, as determined by cardiopulmonary exercise testing (CPET), is the primary endpoint of the trial.

Secondary endpoints include changes in NT-proBNP, left atrial volume index, left ventricular mass index, and post-Valsalva LVOT-G.

These endpoints also include the proportion of patients with ≥1 class improvement in the New York Heart Association (NYHA) functional class and the change from baseline to Week 24 in the Kansas City Cardiomyopathy Questionnaire (KCCQ) score.

An open-label extension clinical study, Follow-Up, Open-Label, Research Evaluation of Sustained Treatment with Aficamten in HCM (FOREST-HCM), will be initiated further to enrol participants who complete the MAPLE-HCM study.