FDA Approves Etripamil Nasal Spray for Acute PSVT

Concurrent with the FDA acceptance, Milestone is also announcing today the extension of its $75.0 million purchase and sale agreement (Royalty Purchase Agreement) with existing shareholder, RTW Investments, LP and certain of its affiliates (RTW) until December 31, 2025. The proceeds from the Royalty Purchase Agreement are expected to aid a successful planned launch of CARDAMYST in PSVT following expected FDA approval and satisfaction of other customary closing conditions.

“The FDA’s acceptance for review of our response to the CRL is a key milestone for CARDAMYST and we look forward to working with the Agency toward a potential approval decision later this year,” said Joe Oliveto, President and Chief Executive Officer of Milestone Pharmaceuticals. “We are also pleased to amend our Royalty Purchase Agreement with RTW, underscoring their ongoing commitment to Milestone. The anticipated funds will position us well to execute on the commercial launch as we work to get CARDAMYST into the hands of patients with PSVT in need of a new treatment.”

Amendment of Royalty Purchase Agreement with RTW

In March 2023, Milestone entered into the Royalty Purchase Agreement with RTW, pursuant to which RTW agreed to purchase, following the FDA approval (subject to certain conditions) of etripamil on or prior to September 30, 2025 (Approval Date), the right to receive a tiered royalty payments on the annual net product sales of etripamil in the United States, in exchange for a purchase price of $75.0 million. On July 10, 2025, Milestone has amended its Royalty Purchase Agreement (the Amendment) to provide for a three-month extension of the Approval Date. Pursuant to the Amendment, in order to receive the $75 million purchase price, Milestone must receive marketing approval of etripamil from the FDA on or prior to December 31, 2025, satisfy the other customary closing conditions. This represents a contingent future source of funding for Milestone.

Milestone Response to the CRL

Milestone received a Complete Response Letter (CRL) from the FDA in March 2025. A Type A meeting was held with the Agency in early June 2025 to clarify the outstanding items and reach alignment with the FDA on the requirements for the Company’s response to the CRL. Informed by the FDA meeting, Milestone submitted the response to the CRL on June 13, 2025. Included in that response were the results of additional in-vitro studies conducted to meet the updated FDA guidance on nitrosamines, which had been updated since the original NDA submission. Further, in response to the FDA’s need to conduct a pre-approval inspection of a manufacturing testing facility, Milestone transferred the duties of that facility to other contracted vendors that have a relatively recent inspection history with FDA.

The FDA has not raised any concerns regarding the clinical section of the NDA.

About Etripamil

Etripamil is Milestone's lead investigational product. It is a novel calcium channel blocker nasal spray under clinical development for frequent and often highly symptomatic episodes of PSVT and AFib-RVR. It is designed as a self-administered rapid response therapy for patients, thereby bypassing the need for immediate medical oversight. If approved, etripamil is intended to provide health care providers with a new treatment option to enable on-demand care and patient self-management. This portable, self-administered treatment may provide patients with active management and a greater sense of control over their condition. CARDAMYST™, the conditionally approved brand name for etripamil nasal spray, is well studied with a robust clinical trial program that includes a completed Phase 3 clinical-stage program for the treatment of PSVT and Phase 2 trial for the treatment of patients with AFib-RVR.