Generic name: fostamatinib
Brand name: Tavalisse
Dosage form: oral tablet (100 mg; 150 mg)
Drug class: Miscellaneous coagulation modifiers

Medically reviewed by  A Ras MD.

What is fostamatinib used for?

Fostamatinib is a prescription medicine that is used to treat immune thrombocytopenia (ITP).


Fostamatinib is a tyrosine kinase inhibitor. TAVALISSE is formulated with the disodium hexahydrate salt of fostamatinib, a phosphate prodrug that converts to its pharmacologically active metabolite, R406, in vivo.

The chemical name for fostamatinib disodium hexahydrate is disodium (6-[[5-fluoro-2-(3,4,5-trimethoxyanilino) pyrimidin-4-yl]amino]-2,2-dimethyl-3-oxo-pyrido[3,2-b][1,4]oxazin-4-yl)methyl phosphate hexahydrate. The molecular formula is C23H24FN6Na2O9P∙6H2O, and the molecular weight is 732.52. The structural formula is:


Fostamatinib disodium is a white to off-white powder that is practically insoluble in pH 1.2 aqueous buffer, slightly soluble in water, and soluble in methanol.

Each TAVALISSE oral tablet contains 100 mg or 150 mg fostamatinib, equivalent to 126.2 mg or 189.3 mg fostamatinib disodium hexahydrate, respectively.

The inactive ingredients in the tablet core are mannitol, sodium bicarbonate, sodium starch glycolate, povidone, and magnesium stearate. The inactive ingredients in the film coating are polyvinyl alcohol, titanium dioxide, polyethylene glycol 3350, talc, iron oxide yellow, and iron oxide red.

Mechanism of Action

Fostamatinib is a tyrosine kinase inhibitor with demonstrated activity against spleen tyrosine kinase (SYK). The major metabolite of fostamatinib, R406, inhibits signal transduction of Fc-activating receptors and B-cell receptor. The fostamatinib metabolite R406 reduces antibody-mediated destruction of platelets.

Before taking fostamatinib, tell your doctor:

For all patients taking fostamatinib:

  • If you are allergic to fostamatinib; any part of this medicine; or any other drugs, foods, or substances. Tell your doctor about the allergy and what signs you had.
  • If you take any drugs (prescription or OTC, natural products, vitamins) that must not be taken with fostamatinib, like certain drugs that are used for HIV, infections, or seizures. There are many drugs that must not be taken with fostamatinib.
  • If you are breast-feeding. Do not breast-feed while you take fostamatinib or for 1 month after you stop fostamatinib.


  • If the patient is a child. Do not give fostamatinib to a child.

This is not a list of all drugs or health problems that interact with fostamatinib.

Tell your doctor and pharmacist about all of your drugs (prescription or OTC, natural products, vitamins) and health problems. You must check to make sure that it is safe for you to take fostamatinib with all of your drugs and health problems. Do not start, stop, or change the dose of any drug without checking with your doctor.

What are some things I need to know or do while I take fostamatinib?

  • Tell all of your health care providers that you take fostamatinib. This includes your doctors, nurses, pharmacists, and dentists.
  • Have blood work checked as you have been told by the doctor. Talk with the doctor.
  • High blood pressure has happened with fostamatinib. Have your blood pressure checked as you have been told by your doctor.
  • This medicine may cause diarrhea. If you get diarrhea, talk with your doctor about ways to lower this effect. Do not stop taking fostamatinib without talking with your doctor.
  • You may have more chance of getting an infection. Wash hands often. Stay away from people with infections, colds, or flu.
  • If you are 65 or older, use fostamatinib with care. You could have more side effects.
  • This medicine may cause fertility problems. This may affect being able to have children. Talk with the doctor.
  • This medicine may cause harm to the unborn baby if you take it while you are pregnant.
  • If you are able to get pregnant, a pregnancy test will be done to show that you are NOT pregnant before starting fostamatinib. Talk with your doctor.
  • Use birth control that you can trust to prevent pregnancy while taking fostamatinib and for 1 month after stopping fostamatinib.
  • If you get pregnant while taking fostamatinib or within 1 month after your last dose, call your doctor right away.

How is fostamatinib best taken?

Use fostamatinib as ordered by your doctor. Read all information given to you. Follow all instructions closely.

  • Take with or without food.
  • Keep taking fostamatinib as you have been told by your doctor or other health care provider, even if you feel well.

What do I do if I miss a dose?

  • Skip the missed dose and go back to your normal time.
  • Do not take 2 doses at the same time or extra doses.

What are the side effects of fostamatinib that I need to call my doctor about immediately?

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

  • Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
  • Signs of high blood pressure like very bad headache or dizziness, passing out, or change in eyesight.
  • Signs of liver problems like dark urine, feeling tired, not hungry, upset stomach or stomach pain, light-colored stools, throwing up, or yellow skin or eyes.
  • Severe diarrhea.
  • Diarrhea that will not go away.
  • Feeling confused.
  • Chest pain.
  • Shortness of breath.
  • Low white blood cell counts have happened with fostamatinib. This may lead to a higher chance of getting an infection. Call your doctor right away if you have signs of infection like fever, chills, or sore throat.

What are some other side effects of fostamatinib?

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:

  • Diarrhea.
  • Upset stomach.
  • Dizziness.
  • Signs of a common cold.
  • Belly pain.
  • Feeling tired or weak.

These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.

You may report side effects to the FDA at 1-800-332-1088. You may also report side effects at

If overdose is suspected:

If you think there has been an overdose, call your poison control center or get medical care right away. Be ready to tell or show what was taken, how much, and when it happened.

How do I store and/or throw out fostamatinib?

  • Store at room temperature.
  • Store in a dry place. Do not store in a bathroom.
  • Store in the original container. Do not take out the antimoisture cube or packet.
  • Keep all drugs in a safe place. Keep all drugs out of the reach of children and pets.
  • Throw away unused or expired drugs. Do not flush down a toilet or pour down a drain unless you are told to do so. Check with your pharmacist if you have questions about the best way to throw out drugs. There may be drug take-back programs in your area.