Sanofi Faces Regulatory Setback As FDA Issues Complete Response Letter For Tolebrutinib Program

Sanofi’s multiple sclerosis treatment ambitions hit a snag as the U.S. Food and Drug Administration delivered a complete response letter regarding tolebrutinib’s new drug application for non-relapsing secondary progressive multiple sclerosis (nrSPMS) in adults. The pharmaceutical giant had been bracing for extended timelines since mid-December, when it signaled the regulatory review would push past the originally scheduled December 28, 2025 decision date.

FDA’s Decision Disappoints Development Hopes

The rejection through a complete response letter marks an unexpected turn for the investigational oral therapy. Tolebrutinib, designed as a brain-penetrant Bruton’s tyrosine kinase inhibitor, was positioned to address smoldering neuroinflammation—a critical factor driving disability progression in MS patients. Sanofi’s research leadership expressed frustration with the FDA’s stance, emphasizing the company’s belief that regulators should weigh input from scientific experts, clinical practitioners, and patient advocates when making such determinations. The firm indicated it remains open to dialogue with the agency to chart a viable pathway forward.

Timeline Adjustments And Regulatory Expectations

The company had already flagged in mid-December that FDA guidance would likely extend into Q1 2026. In response to agency requests, Sanofi submitted an expanded access protocol for the treatment. This extended review process prompted the company to initiate an impairment assessment under IFRS standards (IAS 36) on tolebrutinib’s intangible asset valuation, with findings to surface alongside Sanofi’s full-year 2025 financial results scheduled for January 2026. Management confirmed this complete response letter and subsequent testing would not materially impact net business income, diluted earnings per share, or the company’s 2025 financial guidance.

Global Regulatory Landscape

Despite the U.S. setback, tolebrutinib maintains forward momentum in other markets. The drug received provisional approval in the United Arab Emirates during July 2025 for nrSPMS treatment and to decelerate disability accumulation independent of relapse activity. European Union regulatory processes and reviews in additional jurisdictions worldwide remain underway.

Market Reaction

Sanofi’s stock (SNY) closed regular trading on December 23, 2025 at $48.32, recording a modest gain of $0.29 or 0.60%. After-hours activity showed the security trading flat, reflecting measured investor sentiment following the complete response letter disclosure. The regulatory disappointment will likely influence how the market views Sanofi’s pipeline progress through the coming quarters.