An oral drug called fenebrutinib reduced relapse rates by up to 59 percent compared with teriflunomide (Aubagio) in two phase 3 clinical trials. Fenebrutinib is an experimental, oral disease-modifying therapy (DMT) used to treat relapsing forms of MS.

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Earlier results from another phase 3 study showed that fenebrutinib performed similarly to ocrelizumab (Ocrevus) at slowing disability progression in people with primary progressive MS (PPMS). Ocrelizumab is considered a high-efficacy therapy — a treatment that strongly suppresses the immune activity that drives MS and can significantly reduce relapses and new brain lesions. High-efficacy therapies are mostly given by infusion or injection.

If approved by the U.S. Food and Drug Administration (FDA), fenebrutinib could become the first high-efficacy oral DMT designed to treat both relapsing MS and PPMS, potentially offering a tablet alternative to some infusion-based treatments.

Independent experts say the findings are promising. “If approved, fenebrutinib could expand our therapeutic tool kit with an oral, higher-efficacy option that targets B-cell biology and innate immune mechanisms in a novel way,” said Dr. Carrie Hersh, associate professor of neurology at Cleveland Clinic Lerner College of Medicine, in an interview with NeurologyLive.

How Does Fenebrutinib Work?

Fenebrutinib belongs to a class of drugs called Bruton’s tyrosine kinase (BTK) inhibitors.

These medications target immune system activity that contributes to inflammation. In MS, the immune system mistakenly produces inflammation and attacks the protective covering of nerve fibers in the brain and spinal cord, which can lead to symptoms and relapses.

Fenebrutinib blocks a protein called BTK, which plays a role in the activity of several immune cells, including:

• B cells, which help drive inflammatory attacks linked to relapses
• Microglia, immune cells in the brain that may contribute to ongoing nerve damage

Researchers hope that by targeting both types of immune activity, the drug could affect both relapses and longer-term disease progression.

What Did the Clinical Trials Find?

The new results come from two large phase 3 clinical trials called FENhance 1 and FENhance 2. Together, these trials studied nearly 1,500 adults with relapsing forms of MS.

Participants were randomly assigned to receive either fenebrutinib tablets twice daily or teriflunomide tablets once daily.

Both studies lasted about two years (at least 96 weeks).

Key findings included:

• In the FENhance 1 trial, fenebrutinib reduced MS relapse rates by 51 percent compared with teriflunomide.
• In the FENhance 2 trial, relapse rates were reduced by 59 percent compared with teriflunomide.
• MRI scans showed significant reductions in brain lesions, which are markers of MS disease activity.

Based on the observed relapse rates, researchers estimated that someone treated with fenebrutinib might experience about one relapse every 17 years on average. It’s important to note this is a projection based on 96 weeks of trial data, rather than a long-term observed outcome.

Side Effects and Safety

As with all medications, fenebrutinib can cause side effects. In earlier clinical trials of fenebrutinib for rheumatoid arthritis, the most commonly reported side effects included:

• Nausea
• Headache
• Anemia
• Chest infections

Researchers in the MS trials also monitored liver enzyme elevations, which can be a sign of liver irritation. These changes occurred at similar rates in people taking fenebrutinib and those taking teriflunomide.

Across the two MS studies:

• Eight deaths occurred among participants taking fenebrutinib.
• One death occurred among participants taking teriflunomide.

According to Roche, the drug’s developer, the deaths had various causes and occurred at different points during treatment. Further analyses are underway to better understand these findings.

Additional safety data from the trials are expected to be presented when researchers share the full results at upcoming medical conferences. Those detailed results will help clarify how fenebrutinib compares with existing MS treatments.

What These Results Could Mean for People With MS

Many disease-modifying therapies used to treat MS — particularly highly effective ones — are given by infusion or injection.

If fenebrutinib is approved, it could offer a new oral treatment option to people living with either relapsing MS or PPMS.

The drug is not yet approved for MS treatment. The company developing fenebrutinib plans to submit the phase 3 trial results to regulators such as the FDA for review.

If you’re interested in new MS treatments, talk with your neurologist about how emerging therapies may fit into your overall treatment plan.

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On MyMSTeam, people living with MS share their experiences with symptoms, treatments, and daily life with the condition.

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