Dive Brief:

• The Food and Drug Administration has required Sanofi to stop treating some patients in Phase 3 trials of an experimental multiple sclerosis drug and pause enrollment in the studies in an effort to prevent more cases of drug-induced liver damage. Only volunteers in the trial for more than 60 days will continue receiving treatment.

• The decision affects U.S.-based patients in four multiple sclerosis trials and a separate study in myasthenia gravis, which together are expected to include more than 4,000 volunteers. After consulting with the regulator, Sanofi will more closely monitor patients’ liver function and exclude those at risk of liver problems.

• Called tolebrutinib, the drug was one of three Sanofi gained when it bought Californian biotech Principia Biopharma for $3.7 billion in 2020. One drug from that deal, being tested in an immune-related skin condition, has already failed in a clinical trial, although research continues.

Dive Insight:

Multiple sclerosis has a growing number of treatment options, including some newer pills that some patients prefer over older injectable or intravenous drugs that were once their only choices. Sanofi is in a race with Roche, Merck KGaA and Biogen to prove a different type of pill, known as a Bruton’s tyrosine kinase inhibitor and widely used in blood cancers, can help too.

Sanofi’s trials are expected to produce results next year, so any setback could hurt its chances of being the first to deliver data to the FDA. On Thursday, the company said it’s enrolled 2,000 people in its trials so far.

The French drugmaker didn’t specify the side effect patients experienced, other than describing it as “a limited number of cases of drug-induced liver injury.” The partial clinical hold ordered by the FDA only applies to patients at U.S. trial sites. Enrollment continues elsewhere with the new safeguards, Sanofi said.

In a note to clients, SVB Securities analyst David Risinger wrote that he believes most of the trial enrollment was occurring in non-U.S. sites, “so a late 2023 readout in relapsing [multiple sclerosis] could still be possible.”

Two of the trials are testing the drug in relapsing MS, the most common form of the disorder, while the others are evaluating treatment in progressive forms and myasthenia gravis. The 900-patient trials in relapsing disease compare tolebrutinib to Sanofi’s marketed medicine, Aubagio. The others pit Sanofi’s drug against a placebo.

Merck, meanwhile, has completed enrolling patients in two trials that test its BTK inhibitor against Aubagio in relapsing multiple sclerosis, according to a federal clinical trial database. Merck expects results next year as well.

Roche’s program may take longer, as it doesn’t expect to complete trials until 2025. The Swiss drugmaker is testing its drug prospect against another marketed therapy, Ocrevus, in a progressive form of MS. Two trials in relapsing disease are underway, too.

Biogen’s program is still in Phase 2 studies.