Rilzabrutinib for immune thrombocytopenia

Last updated July 2, 2025, by Lindsey Shapiro, PhD
Fact-checked by Joana Carvalho, PhD

What is rilzabrutinib for immune thrombocytopenia?

Rilzabrutinib is an experimental oral therapy being investigated as a possible treatment for immune thrombocytopenia (ITP). It is currently under regulatory review in China, the European Union, and the U.S., where a regulatory decision is expected in August 2025.

ITP is an autoimmune disease wherein the immune system mistakenly attacks and destroys platelets, the cell fragments needed for blood clotting. Rilzabrutinib aims to prevent platelet destruction by selectively inhibiting Bruton’s tyrosine kinase (BTK), an enzyme important for the function of the immune cells that drive these attacks.

The treatment is designed with technology that enables it to strongly, selectively, and durably bind to BTK — thus potentially avoiding off-target side effects — while also being reversible.

Rilzabrutinib has earned regulatory statuses in the U.S. that are intended to speed its clinical development for ITP, including orphan drug and fast track designations. It is being developed by Sanofi, which is also testing it as a possible treatment for several other disorders.

Therapy snapshot

How will rilzabrutinib be administered in immune thrombocytopenia?

In clinical trials involving ITP patients, rilzabrutinib was administered as oral tablets. In a pivotal Phase 3 trial, it was given at a dose of 400 mg, taken twice daily.

Rilzabrutinib in immune thrombocytopenia clinical trials

The regulatory applications seeking the approval of rilzabrutinib for ITP are supported mainly by data from the ongoing Phase 3 LUNA 3 trial (NCT04562766) involving adults and adolescents, ages 10 and older, with persistent or chronic ITP who have not responded adequately to standard therapies or could not tolerate them. Results from LUNA 3 showed that:

• Significantly more adult patients on rilzabrutinib than those on a placebo achieved a durable platelet response after about six months, where platelet counts reached a certain threshold without the need for rescue therapy.
• Secondary endpoints related to fatigue, bleeding, and the need for rescue therapies also significantly favored rilzabrutinib over the placebo.

Data from an ongoing Phase 1/2 clinical trial (NCT03395210) involving adults with previously treated ITP similarly showed that rilzabrutinib led to rapid and durable platelet responses, and its benefits and safety profile were sustained long-term.

Common side effects of rilzabrutinib

Rilzabrutinib has generally been found to be safe in ITP clinical trials, with most side effects being mild to moderate in severity and temporary.

The most common treatment-related side effects reported among adult participants in the LUNA 3 trial include:

• diarrhea
• nausea
• headache
• abdominal pain.

Uncommon but serious side effects considered related to rilzabrutinib in the trial included low blood levels of neutrophils, a type of infection-fighting immune cell, and a blood clot in the lower leg. A few cases of treatment-related infections that were at least moderate in severity occurred in people on rilzabrutinib.

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