Definition
Fostamatinib is an oral prodrug that is rapidly converted in vivo to the active metabolite R406, a potent and selective inhibitor of spleen tyrosine kinase (Syk). It is used as a therapeutic agent for certain autoimmune hematologic disorders.
Overview
Fostamatinib (development code R788) was discovered by Rigel Pharmaceuticals and later approved by the United States Food and Drug Administration (FDA) in 2018 for the treatment of chronic immune thrombocytopenia (ITP) in adults who have had insufficient response to prior therapies. The drug is marketed in the United States under the brand name Tavalisse. By inhibiting Syk—a key kinase in B‑cell receptor signaling and Fc receptor–mediated pathways—fostamatinib reduces antibody‑driven destruction of platelets and modulates other immune cell activities. Clinical trials have demonstrated increased platelet counts in a proportion of patients with refractory ITP, leading to its regulatory approval. Additional investigations have evaluated fostamatinib in rheumatoid arthritis, lupus, and other autoimmune conditions, though it has not received approval for these indications.
Etymology / Origin
The name “fostamatinib” follows the conventional nomenclature for kinase inhibitors, wherein the suffix “‑tinib” denotes a therapeutic agent that targets tyrosine kinases. The prefix “fos‑” reflects the presence of a phosphate group; fostamatinib is a phosphate ester designed to enhance oral absorption before enzymatic conversion to the active, non‑phosphorylated metabolite R406.
Characteristics
| Property | Detail |
|---|---|
| Chemical formula | C₂₈H₃₀N₅O₈P |
| Molecular weight | ≈ 560.6 g·mol⁻¹ |
| Mechanism of action | Prodrug → R406 (active Syk inhibitor). Inhibition of Syk blocks downstream signaling from B‑cell receptors and Fcγ receptors, decreasing immune‑mediated platelet clearance. |
| Pharmacokinetics | Oral administration; rapid conversion by intestinal and hepatic alkaline phosphatases to R406. R406 reaches peak plasma concentrations within 1–2 h; terminal elimination half‑life ≈ 15 h. |
| Metabolism & excretion | Primarily hepatic metabolism; excreted via feces and urine as unchanged R406 and metabolites. |
| Adverse effects (common) | Hypertension, diarrhoea, nausea, neutropenia, elevated liver transaminases, headache. |
| Regulatory status | FDA‑approved (2018) for chronic ITP; approved in the European Union (2021) under the same indication. Not approved for rheumatoid arthritis or other autoimmune diseases. |
Related Topics
- Spleen Tyrosine Kinase (Syk) – The intracellular kinase targeted by fostamatinib; central to B‑cell receptor signaling and Fc receptor–mediated immune responses.
- Immune Thrombocytopenia (ITP) – An autoimmune disorder characterized by low platelet counts; primary therapeutic target for fostamatinib.
- Kinase Inhibitors – A class of drugs that block enzymatic activity of kinases; includes other agents ending in “‑tinib” (e.g., imatinib, ruxolitinib).
- R406 – The active metabolite of fostamatinib; studied independently in preclinical and early‑clinical settings.
- Tavalisse – Commercial brand name for fostamatinib in the United States.
- Autoimmune Hematologic Disorders – Conditions such as autoimmune hemolytic anemia and Evans syndrome, for which Syk inhibition is under investigation.
All information presented is based on publicly available regulatory documents, peer‑reviewed clinical studies, and pharmacological references up to the knowledge cutoff of September 2021.