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Milestone Pharmaceuticals MIST recently announced that the FDA has issued a Complete Response Letter (“CRL”) for its New Drug Application (“NDA”) seeking approval for CARDAMYST (etripamil) nasal spray. This drug is being developed for the treatment of paroxysmal supraventricular tachycardia (PSVT), a condition characterized by sudden, rapid heartbeats.
While the CRL raises no concerns about the clinical safety or efficacy of etripamil, it points to two key Chemistry, Manufacturing, and Controls (“CMC”) issues that must be addressed before approval can be granted.
Shares of MIST plunged 66.2% since the CRL issuance, reflecting the delay in the launch of Cardamyst. The company’s shares have lost 67.8% so far this year against the industry’s 2.2% growth. The S&P 500 Index has declined 5.6% in the same period.
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Key Regulatory Issues Identified
The first issue highlighted by the FDA pertains to nitrosamine impurities. The agency has requested additional data based on newly issued draft guidance that was published after MIST’s NDA submission. Nitrosamines, which can pose carcinogenic risks when present above acceptable levels over prolonged exposure, have become an increasing area of focus for regulatory scrutiny in pharmaceutical products.
The second issue is related to an inspection of a facility involved in the drug’s release testing. This facility underwent a change in ownership during the NDA review, necessitating a compliance evaluation to ensure adherence to Current Good Manufacturing Practices (cGMP).
Analyst and Market Reactions
Despite this regulatory roadblock, analysts remain cautiously optimistic about the drug’s prospects. They are of the view that Milestone Pharmaceuticals can successfully resolve the identified concerns, suggesting a potential commercial launch in 2026. However, this timeline represents a delay from the company’s original expectations of a mid-2025 launch. Given the complexity of regulatory processes, even this revised estimate could be subject to further adjustments depending on the pace of resolution and regulatory feedback.
MIST’s Response and Next Steps
Milestone Pharmaceuticals has responded swiftly to the CRL, stating its intent to request a Type A meeting with the FDA to clarify the path forward. The company has emphasized its commitment to working collaboratively with the agency to address the outstanding issues and advance the approval process. This is not the first regulatory challenge faced by the company. In December 2023, MIST received a refusal-to-file letter from the FDA, requiring modifications to its initial NDA submission before it could be considered for full review.