Fostamatinib

580.4595042

580.46

1533716-785-6

SQ8A3S5101

C95222

B02BX|B - Blood and blood forming organs

187

2.12

1.5±0.1 g/cm3

814.2±75.0 °C at 760 mmHg

446.2±37.1 °C

1.629

Neither fostamatinib or R406 were found to be carcinogenic or mutagenic. Fostamatinib can cause embryo-fetal mortality or developmental abnormalities at exposures of 0.3-10 times the maximum recommended human dose. Serious adverse effects include hypertension, neutropenia, diarrhea, and hepatotoxicity

In prelicensure controlled trials, serum aminotransferase elevations above 3 times ULN arose in 9% of fostamatinib treated subjects but in none of the placebo recipients. ALT values above 5 times ULN occurred in 5% of treated subjects. These elevations were typically transient but led to early discontinuations in a proportion of patients, but more often resolved even without dose adjustment. In prelicensure studies, there were no instances of clinically apparent liver injury attributed to fostamatinib. Since approval and more widescale availability of fostamatinib, there have been no published reports of hepatotoxicity associated with its use, although it has had limited general use.

R406 is 98.3% bound to plasma proteins.

Fostamatinib is indicated for use in the treatment of chronic immune thrombocytopenia (ITP) in patients who have had insufficient response to previous therapy.|FDA Label|Tavlesse is indicated for the treatment of chronic immune thrombocytopenia (ITP) in adult patients who are refractory to other treatments.|Treatment of idiopathic thrombocytopenic purpura as a model for immunomodulation|Treatment of chronic idiopathic arthritis (including rheumatoid arthritis, ankylosing spondylarthritis, psoriatic arthritis and juvenile idiopathic arthritis)

Fostamatinib is an orally available small molecule inhibitor of spleen tyrosine kinase that is used to treat chronic immune thrombocytopenia. Fostamatinib is associated with transient and usually mild elevations in serum aminotransferase levels during therapy but has yet to be linked to instances of clinically apparent acute liver injury.

Hematologic Growth Factors

The active metabolite of fostamatinib, R406, inhibits signal transduction by Fcγ receptors involved in the antibody-mediated destruction of platelets by immune cells in chronic ITP. This results in increased platelet counts in this population. R406 produces inhibition of T and B lymphocyte activation by T-cell receptors (TCRs) and B-cell receptors (BCRs) respectively. It can also inhibit signalling via Fcε receptors which could have applications in treating allergic symptoms through prevention of mast cell degranulation. Inhibition of Fc receptor signalling system also affected by R406 suppresses both dendritic cell maturation and antigen presentation and may contribute to the effects of fostamatinib. As a knock-on effect of disabling signal transduction from Fc receptors, TCRs, and BCRs, the production of inflammatory mediators and cytokines like tumour necrosis factor α, leukotriene C4, interleukin-8, and granulocyte-macrophage colony-stimulating factor. Fostamatinib can produce hypertension through off-target effects

Fostmatinib is the methylene phosphate prodrug of R406, the active metabolite. It is extensively hydrolyzed by intestinal alkaline phosphatase. Only negligible amounts of fostamatinib enter systemic circulation. R406 has an absolute bioavailability of 55% and reaches peak plasma concentrations in approximately 1.5 h. Administration with a high calorie, high fat meal increases exposure by 23% and the maximum plasma concentration by 15%. This may lengthen time to peak plasma concentration to approximately 3 h. Exposure to R406 is known to be dose proportional up to 200 mg twice daily. R406 accumulates 2-3 fold with twice daily dosing at 100-160 mg.|About 80% of R406 is excreted in the feces, primarily as the O-glucuronide conjugate and the O-desmethyl metabolite produced by gut bacteria. The remaining 20% is excreted in the urine as the N-glucuronide conjugate.|R406 has an apparent oral volume of distribution of approximately 400 L.|R406 has an apparent oral clearance of approximately 300 mL/min.

Fostamatinib is metabolized in the gut by alkaline phosphatase to the active metabolite R406. R406 is further oxidized by CYP3A4 and glucuronidated by UGT1A9. Plasma metabolites found include an O-glucuronide conjugate, an N-glucuronide conjugate, an O-desmethyl metabolite, and a sulfate conjugate. A 3,5 benzene diol metabolite forms in the feces via processing of the O-desmethyl metabolite by gut bacteria.

R406 has a half-life of elimination of approximately 15 h.

The active metabolite of fostamatinib, R406, is an inhibitor of spleen tyrosine kinase (Syk). It binds reversibly to the ATP binding pocket with high affinity (Ki = 30nM), inhibiting the kinase activity with an IC50 of 41nM. Syk is a cytosolic protein kinase and part of the signalling cascade which occurs with Fc receptors, TCRs, and BCRs. It contains two src homology 2 (SH2) domains separated by a linker domain. These SH2 domains bind to tyrosine residues on the immunoreceptor tyrosine-based activating motif phosphorylated by Lyn, another kinase in the cascade. This motif is located on the cytoplasmic regions of several immune receptors including Fc receptors, TCRs, BCRs, and natural killer cell receptors. The flexibility provided by the linker enables the protein to bind to many receptor types. Inhibition of Syk suppresses downstream signal transduction. While Syk plays a role in some pathways involved in the generation of the oxidative burst by neutrophils or phagocytosis by macrophages, R406 does not have a significant effect on these processes. This is likely due to redundant pathways which do not involve Syk. Similarly Syk does not produce significant effects on platelet activation despite its involvement in glycoprotein IV and integrin based signalling. Activation of antibody-dependent cell-mediated toxicity by natural killer cells is also unaffected despite the involvement of Syk in Fc receptor signalling. R406 binds to the adenosine A3 receptor as an antagonist as well as the adenosine and monoamine uptake transporters as an inhibitor. It has also been found to be an inhibitor of UDP glucuronosyltransferase UGT1A1, phosphodiesterase PDE5, fatty acid amide hydrolase, 5-lipoxygenase, cathepsin L, and cathepsin S. R406 appears to inhibit a wide range of kinases at higher concentrations. It is thought that inhibition of some of these targets may be responsible for the increase in blood pressure seen with fostamatinib.

fostamatinib

Human drugs -> Tavlesse -> EMA Drug Category|Other systemic hemostatics -> Human pharmacotherapeutic group|Human Drugs -> EU pediatric investigation plans|Human Drugs -> FDA Approved Drug Products with Therapeutic Equivalence Evaluations (Orange Book) -> Active Ingredients