Cardamyst (Etripamil): The First FDA-Approved Nasal Spray for PSVT — Mechanism and Clinical Data Analysis

More than 2 million people in the United States live with paroxysmal supraventricular tachycardia (PSVT), a condition in which the heart can suddenly shift into a very rapid rhythm without warning. For more than 30 years, there had been no new FDA approval specifically for this condition. In December 2025, the approval of Cardamyst changed that regulatory gap.

Cardamyst is the brand name for etripamil, a rapid-acting L-type calcium channel blocker delivered as a nasal spray. It was developed by Milestone Pharmaceuticals and approved by the FDA for conversion of acute symptomatic PSVT episodes to sinus rhythm in adults. The key differentiator is the care model: the therapeutic logic moves from an exclusively hospital-based intervention toward an approved out-of-hospital framework, always under medical supervision and according to prescribing information.

Etripamil acts as an L-type calcium influx inhibitor. At the AV node, inhibition of calcium influx slows AV nodal conduction and can interrupt the reentry circuit that sustains tachycardia. Through this mechanism, it may restore sinus rhythm in PSVT. Its rapid pharmacokinetic profile is a central element of its pharmacological differentiation.

The RAPID trial was a randomized, double-blind, placebo-controlled, multicenter, event-driven Phase 3 study with 692 randomized patients with a history of symptomatic PSVT. Of these, 255 perceived an episode and received study drug, while 184 episodes were confirmed by blinded adjudication as PSVT. In the primary analysis, Kaplan-Meier estimates for conversion to sinus rhythm within 30 minutes were 64% with Cardamyst versus 31% with placebo, with a hazard ratio of 2.6, 95% CI 1.7 to 4.2, and p<0.001. Median time to conversion was 17.2 minutes with Cardamyst versus 53.5 minutes with placebo.

The FDA label includes specific information on the approved indication, clinical use, limitations, and safety. In this article, label information is referenced only as regulatory context. It is not reproduced as practical instruction and does not replace medical assessment, prescribing information, or clinical decision-making.

In the clinical-trial and label context, the most common adverse events were mainly local and transient, including nasal discomfort, nasal congestion, and rhinorrhea. The FDA label also highlights warnings related to hemodynamic effects. This is important because the drug acts on cardiac conduction and should not be interpreted as a simple local nasal product.

Cardamyst has important contraindications in specific cardiac contexts, including certain forms of heart failure, pre-excitation syndromes, and higher-grade AV conduction disorders. The editorial conclusion is straightforward: the convenience of a nasal formulation should not be confused with absence of risk.

Etripamil is also being evaluated for atrial fibrillation with rapid ventricular rate (AFib-RVR), based on positive results from the ReVeRA Phase 2 trial published in Circulation: Arrhythmia and Electrophysiology. If this development path progresses, the molecule could gain a second research and regulatory chapter beyond the PSVT indication.

The Cardamyst approval is important not because it introduces an unknown pharmacological axis, but because it moves a calcium-channel-blocking mechanism into a rapid-acting nasal formulation for episodic PSVT. From a research and regulatory perspective, the key interest lies in the convergence of pharmacokinetics, formulation science, AV nodal electrophysiology, and the real need for out-of-hospital episode management.