Rilzabrutinib is an orally active, selective Bruton’s tyrosine kinase (BTK) inhibitor developed for the treatment of immune-mediated diseases. It is a small-molecule kinase inhibitor designed to provide reversible covalent inhibition of BTK with a controlled residence time at the target.
Rilzabrutinib received its first U.S. approval in August 2025 under the brand name WAYRILZ for the treatment of adults with persistent or chronic immune thrombocytopenia (ITP) who have had an insufficient response to a previous treatment.
Rilzabrutinib API
The FDA-approved chemical description gives the molecular formula as C₃₆H₄₀FN₉O₃ and molecular weight as 665.77 Da. FDA also identifies rilzabrutinib as a BTK inhibitor.
Rilzabrutinib is a synthetic small molecule containing a pyrazolo[3,4-d]pyrimidine core linked to a substituted phenoxyphenyl group, piperidine, piperazine and oxetane structural elements.
The molecule contains a fluorine atom and multiple nitrogen and oxygen atoms that contribute to its physicochemical and pharmacological properties. PubChem reports the molecular formula C₃₆H₄₀FN₉O₃ and molecular weight of approximately 665.8 g/mol.
The FDA-approved product describes rilzabrutinib as a white to off-white solid, freely soluble in ethanol, sparingly soluble in isopropyl alcohol and practically insoluble in water.
Rilzabrutinib API is used for development and manufacture of oral pharmaceutical products targeting immune-mediated diseases.
Its first FDA-approved indication is:
Rilzabrutinib has also been investigated in other immune-mediated and inflammatory conditions. These development programs include diseases in which B-cell signaling, Fc-receptor signaling or innate immune pathways contribute to pathological inflammation.
Rilzabrutinib is a selective, covalent, reversible inhibitor of Bruton's tyrosine kinase (BTK). BTK is an intracellular signaling molecule expressed in B cells and several innate immune cell populations.
In B cells, BTK signaling contributes to B-cell activation, survival, proliferation and maturation. In innate immune cells, BTK participates in signaling pathways involving Fc gamma receptors, toll-like receptors and the NLRP3 inflammasome.
In immune thrombocytopenia, rilzabrutinib's pharmacological activity is associated with multiple immune-modulating effects. It can inhibit B-cell activation and interfere with Fcγ receptor-mediated phagocytosis of antibody-coated platelets. It may also reduce pathogenic autoantibody generation through effects on B-cell signaling.
The reversible covalent interaction with BTK provides target engagement while allowing a controlled duration of kinase inhibition.
As a chemically synthesized small-molecule API, Rilzabrutinib requires appropriate pharmaceutical analytical characterization.
Typical quality-control parameters include:
The exact numerical acceptance criteria should be established according to the applicable approved API specification and validated analytical methods. Public FDA labeling provides the identity and physicochemical information but does not constitute a complete public API release specification.
Rilzabrutinib is a synthetic small-molecule pharmaceutical ingredient manufactured through controlled organic synthesis.
A pharmaceutical manufacturing process generally involves:
Particular attention should be given to process-related impurities, residual solvents and solid-state characteristics because these attributes can influence the quality and reproducibility of the finished pharmaceutical product.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 98.0% – 102.0% |