Milestone's CARDAMYST launch gains early traction as cardiovascular biotech ramps spending

Milestone Pharmaceuticals, the dual-listed Canadian-US cardiovascular biotech, reported early commercial momentum for its newly launched nasal-spray heart rhythm therapy and confirmed the start of a late-stage trial in a second, larger indication, as it heads into the most operationally intensive phase in its corporate history.

The Nasdaq-listed Montreal- and Charlotte-based group reported first-quarter results on Wednesday showing $0.2mn of initial product revenue from CARDAMYST, the brand name for etripamil nasal spray, which secured US Food and Drug Administration approval and entered the market roughly eight weeks later in mid-February. Approximately 600 prescriptions had been filled for 560 patients with paroxysmal supraventricular tachycardia, or PSVT, by the end of April, written by around 400 unique prescribers — a measure of early breadth that the company's management said reflected genuine clinical enthusiasm rather than a narrow cluster of early adopters.

CARDAMYST, a self-administered calcium channel blocker, is the first therapy designed to allow patients to acutely treat their own PSVT episodes outside of a clinical setting. The drug effectively bypasses the need for an emergency department visit to convert acute episodes of the rapid heart rhythm disorder back to sinus rhythm — a substantial structural shift in the standard of care, and one Milestone believes underpins the asset's potential commercial reach.

Joseph Oliveto, chief executive, said: "We're excited to report on our first quarter of sales for CARDAMYST for paroxysmal supraventricular tachycardia." He cited the addition of CARDAMYST to the Express Scripts national commercial formulary, effective 27 March, as a significant milestone in securing broad payer access. More than 25 per cent of US commercially insured lives now have coverage for the drug.

The company also confirmed the initiation of a phase 3 registrational programme in atrial fibrillation with rapid ventricular rate, or AFib-RVR, a substantially larger market than PSVT. Clinical site onboarding is under way, with first patient enrolment expected in the second half of 2026. Milestone intends to seek approval via a supplemental new drug application, leveraging the existing PSVT safety database alongside the planned single phase 3 study — an unusually capital-efficient path for a biotech of its size, if the regulatory strategy holds.

International expansion is also progressing. The European Medicines Agency has accepted the company's marketing authorisation application for etripamil in PSVT, with the drug to be marketed under the conditionally approved brand name TACHYMIST. A decision is expected in the first half of 2027. In March, Hong Kong-based Everest Medicines acquired the China rights from Milestone's regional licensing partner Corxel Pharmaceuticals, taking on development, manufacturing and commercialisation responsibilities for Greater China, where a new drug application has been under review with the National Medical Products Administration since January 2025.

The financial profile reflects the realities of an early-stage commercial biotech. Net loss for the quarter widened to $26.1mn, or $0.20 per share, from $20.8mn or $0.31 per share a year earlier, with commercial expenses rising to $15.8mn from $10.4mn as the group built out a 60-strong national sales force targeting cardiologists, electrophysiologists and advanced practice providers. Research and development spending fell to $3.3mn from $5.0mn, reflecting reduced outside service costs, while general and administrative costs were broadly flat at $4.8mn.

Cash, cash equivalents and short-term investments stood at $184.2mn at the end of March, up sharply from $106.0mn at year-end, after Milestone closed a $78mn royalty financing transaction during the quarter. The company expects its liquidity to fund operations into the second half of 2027, including the launch of the phase 3 AFib-RVR programme — a runway that buys time for CARDAMYST adoption to translate into meaningful revenue growth, but that will face increasing scrutiny if the script trajectory does not accelerate from the early base.

The early commercial metrics offer mixed signals for investors. The breadth of prescribers — roughly 400 in the first ten weeks of launch — points to wider clinician interest than a more concentrated launch would imply, and is consistent with management's positioning of CARDAMYST as a paradigm-shifting therapy rather than a niche product. Yet the absolute prescription volume of roughly 600 scripts to date remains modest in commercial terms, with revenue still negligible relative to the cost of supporting a national sales effort and a parallel late-stage development programme.

The deeper investment case turns on the AFib-RVR opportunity. PSVT is a relatively small market, affecting perhaps 600,000 to 1 million people in the US. AFib-RVR represents a substantially larger commercial prize, given the underlying prevalence of atrial fibrillation. A successful phase 3 readout — and a regulatory path that allows Milestone to leverage its existing PSVT approval — could materially re-rate the company's commercial profile. The path to that point, however, requires execution discipline across both the ongoing US launch and the substantial new clinical programme, against a cash runway that, while adequate, does not afford the company unlimited time to deliver.

For now, the first prescription numbers, the formulary win and the start of the AFib-RVR trial provide a credible early-stage narrative. The next quarter's data — particularly on prescription growth, persistence, and the conversion of unique prescribers into repeat users — will be the more decisive test of whether the strategic case can support the spending profile Milestone is now committed to.