Model-Informed Recommendation of Mavacamten Posology for Chinese Adults With Obstructive Hypertrophic Cardiomyopathy

Mavacamten is a cardiac myosin inhibitor for adults with obstructive hypertrophic cardiomyopathy (HCM). Dose optimization is performed 4 weeks after starting mavacamten, guided by periodic echo measurements of Valsalva left ventricular outflow tract gradient (VLVOTg) and left ventricular ejection fraction (LVEF). Previously, a population pharmacokinetic (PPK) model was developed and exposure-response (E-R) of VLVOTg (efficacy) and LVEF (safety) was used to identify the mavacamten titration regimen with the optimal benefit/risk ratio, now included in the US prescribing information. Mavacamten is metabolized primarily by cytochrome P450 2C19 (CYP2C19) (74%), a highly polymorphic enzyme. China has a higher prevalence of poor CYP2C19 metabolizer phenotype compared with the global population; therefore, a previous model was adapted to include Chinese patients with obstructive HCM to identify the optimal dosing regimen for this population. Data from a phase I (healthy Chinese volunteers) and a phase III (EXPLORER-CN, NCT05174416; Chinese patients with obstructive HCM) trial of mavacamten were added to the previous PPK and E-R models, and the observed VLVOTg and LVEF from EXPLORER-CN were successfully simulated. Next, five echocardiography-guided titration regimens (plus the EXPLORER-CN regimen) using representative or equal CYP2C19 phenotypes were simulated. The final simulated regimen recommended with an optimal benefit/risk profile across CYP2C19 phenotypes included: down-titration at Week 4 (if VLVOTg < 20 mmHg), restart at Week 12, and up-titration at Week 12 (for VLVOTg ≥ 30 mmHg and LVEF ≥ 55%), and every 12 weeks thereafter. This supports the previously recommended regimen for Chinese patients with obstructive HCM, now approved by the National Medicinal Products Administration.