Fostamatinib

TAVALISSE

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Pronunciation: fos-ta-MA-ti-nib (TAV-a-lees)

Fostamatinib ballicule: receptor binding, kinetics and half-life diagram — Mechanism of action: Fostamatinib ballicule

What it isAn oral spleen tyrosine kinase (SYK) inhibitor whose active metabolite R406 blocks Fc-receptor and B-cell-receptor signaling to reduce antibody-mediated platelet destruction.

Why this oneUsed for chronic immune thrombocytopenia in adults with an insufficient response to prior therapy.

What limits itCommonly causes hypertension, diarrhea, hepatotoxicity, and neutropenia requiring monitoring, and CYP3A4 inhibitors raise R406 exposure.

Fostamatinib molecular structure (skeletal formula) — Molecular structure: Fostamatinib

Fostamatinib prescription history

Animated chart of estimated U.S. prescriptions per year, Tyrosine kinase inhibitors (2001–2026). Fostamatinib enters in 2018 (estimated).

Principal riskNo FDA boxed warning.

Classes and tags

Kinase inhibitors

Clinical profile

Therapeutic safety burden3 / 4

Overdose danger2 / 4

Weight-gain liability0 / 4

Sedation liability0 / 4

QT / Torsades0 / 4

Direct muscarinic antagonism0 / 4

Embryofetal risk2 / 4

FDA label

Read the full label on DailyMed ↗

NO BOXED WARNINGS

FDA dosing	Population	Start	Target	Max
Chronic immune thrombocytopenia (ITP), insufficient response to prior treatment	Adults	100 mg BID	Lowest dose maintaining platelets >=50 x 10^9/L	150 mg BID

Titration After 4 weeks: increase to 150 mg BID if platelets not >=50 x 10^9/L

Renal Undefined

Hepatic Undefined

Monitor: CBC incl. platelets monthly until stable then regularly; LFTs monthly; BP q2wk until stable dose then monthly. Strong CYP3A4 inhibitors increase active metabolite (R406) exposure - monitor for toxicity, dose-modify if needed

Instructions

With or without food
Missed dose: take next dose at regularly scheduled time
Discontinue after 12 weeks if platelet count insufficient to avoid clinically important bleeding
Dose-reduction ladder for toxicity: 300 -> 200 -> 150 (as 150 mg QAM) -> 100 mg/day; discontinue if <100 mg/day needed

Available strengths

tab 100, 150 mg

Cautions

Hypertension (incl. hypertensive crisis 1%) - monitor BP, treat, dose-reduce/interrupt/discontinue if uncontrolled
Hepatotoxicity (ALT/AST >3x ULN in 9%) - monthly LFTs; interrupt/reduce/discontinue per thresholds
Diarrhea (31%; severe 1%) - supportive care; interrupt for Grade >=3
Neutropenia (6%; febrile 1%) - monitor ANC monthly; interrupt if ANC <1.0 x 10^9/L persisting 72 h
Embryo-fetal toxicity - effective contraception during treatment and >=1 month after

Adverse reactions

Diarrhea, hypertension, nausea, respiratory infection, dizziness, ALT/AST increased, rash, abdominal pain, fatigue, chest pain, neutropenia (>=5% and > placebo)
Serious: febrile neutropenia, diarrhea, pneumonia, hypertensive crisis (each 1%)

Pregnancy Can cause fetal harm (animal embryo-fetal mortality/malformations at >=0.3x human exposure); no human data; advise risk and contraception

Lactation Do not breastfeed during treatment and for >=1 month after last dose (R406 5-10x plasma levels in rodent milk)

Cost

Fostamatinib (TAVALISSE)

Strength		#/mo	generic $/mo	CostPlus
100 mg	tab	60 BID		not offered
150 mg	tab	60 BID		not offered

NADAC is a voluntary CMS survey of what retail community pharmacies pay for the drugs they stock. Fostamatinib is dispensed outside retail pharmacies, so it rarely appears on surveyed invoices.

Generic entry2026

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Self-check

Which active metabolite mediates fostamatinib’s effects?
R406.
How do CYP3A4 inhibitors affect R406 exposure?
Increase it.