The FDA gave Milestone Pharmaceuticals Inc. (MIST) something to celebrate on Friday: approval for Cardamyst, the company's first commercial product. This etripamil nasal spray treats acute symptomatic episodes of paroxysmal supraventricular tachycardia (PSVT) in adults, converting those scary fast heartbeats back to normal sinus rhythm.
For the uninitiated, PSVT is a type of arrhythmia where your heart's upper chambers suddenly decide to beat very fast in brief, unpredictable episodes. Think of it as an electrical "short circuit" in the heart that starts and stops abruptly, bringing along unpleasant companions like palpitations, dizziness, shortness of breath, and chest pain. Not exactly fun.
Breaking a Three-Decade Drought
Here's what makes this approval particularly noteworthy: Cardamyst is the first FDA-approved treatment for PSVT in over 30 years. That's a long time for more than 2 million Americans living with this condition to wait for a new option. The nasal spray is a rapid-acting calcium channel blocker that patients can use when they need it, addressing those highly symptomatic and unpredictable episodes as they happen.
Milestone expects Cardamyst to hit retail pharmacy shelves in the first quarter of 2026, giving patients a self-administered alternative to manage their condition.
The Clinical Evidence
The FDA didn't just hand out this approval on a whim. Cardamyst's approval rests on a substantial clinical trial program with safety data from more than 1,800 participants covering over 2,000 PSVT episodes.
The numbers tell a compelling story. In clinical studies, participants using Cardamyst were two times more likely to convert symptomatic PSVT to normal sinus rhythm and did so more than three times faster compared with placebo.
The RAPID trial hit its primary endpoint convincingly: 64% of participants who self-administered Cardamyst (99 people) converted from supraventricular tachycardia to sinus rhythm within 30 minutes, compared to just 31% on placebo (85 people). At the one-hour mark, that benefit jumped to 73% of participants.
Perhaps most impressively, the median time to conversion was 17 minutes for Cardamyst versus 54 minutes for placebo. When you're experiencing a PSVT episode, that 37-minute difference probably feels like an eternity.
Milestone Pharmaceuticals shares responded enthusiastically to the news, climbing 30.73% to $3.15 during premarket trading on Friday, reaching a new 52-week high.