Sanofi's MS Drug Tolebrutinib Faces FDA Delay Amid Ongoing Development Challenges

Sanofi's journey to bring its investigational multiple sclerosis (MS) drug tolebrutinib to market has encountered another obstacle, as the U.S. Food and Drug Administration (FDA) extends its review period by three months. This development marks the latest in a series of challenges for the French pharmaceutical giant's BTK inhibitor, which has shown promise in certain MS indications despite setbacks in clinical trials.

FDA Postpones Decision on Tolebrutinib

The FDA has pushed back its decision date for tolebrutinib from September 28 to December 28, 2025. This delay comes after Sanofi submitted "additional analyses during the review," which the agency considers a major amendment to the original New Drug Application (NDA). Sanofi remains optimistic, stating they are "confident in the potential positive impact tolebrutinib can provide" and will continue to work closely with the FDA throughout the extended review period.

Mixed Results in Clinical Trials

Tolebrutinib's development has been marked by both successes and setbacks:

• The Hercules study, focusing on non-relapsing secondary progressive multiple sclerosis (nrSPMS), met its primary endpoint by demonstrating a delay in disability progression compared to placebo.
• However, the Gemini 1 and 2 trials, which targeted relapsing MS, failed to show superiority over Sanofi's existing MS drug, Aubagio, in reducing relapses over a 36-month period.

These mixed results led Sanofi to narrow its focus for tolebrutinib to the nrSPMS indication, where it showed the most promise.

Regulatory and Safety Challenges

Tolebrutinib's path to approval has been further complicated by safety concerns:

• Three years ago, the FDA placed a partial hold on enrollment for all three phase 3 trials due to cases of drug-induced liver injury associated with tolebrutinib exposure.
• Despite these challenges, Sanofi has pursued the drug's development, highlighting its potential to address unmet needs in MS treatment.

The pharmaceutical company's perseverance in developing tolebrutinib underscores the significant market opportunity in MS therapeutics, as well as the complexities involved in bringing novel treatments to patients with chronic neurological disorders.