Fostamatinib is used to treat thrombocytopenia (less than a normal number of platelets) in adults with chronic immune thrombocytopenia (ITP; an ongoing condition that may cause unusual bruising or bleeding due to an abnormally low number of platelets in the blood) who were not helped with another treatment. Fostamatinib is in a class of medications called kinase inhibitors. It works by reducing platelet destruction.

Side Effects Of Fostamatinib

Fostamatinib may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

  • diarrhea
  • nausea
  • dizziness
  • rash
  • abdominal pain
  • fatigue

Some side effects can be serious. If you experience any of these symptoms, call your doctor immediately or get emergency medical treatment:

  • severe diarrhea
  • headache, confusion, dizziness, chest pain, or shortness of breath
  • pain in the upper right part of the stomach
  • yellowing of the skin or eyes
  • dark-colored urine
  • nausea
  • vomiting

Fostamatinib may cause other side effects. Call your doctor if you have any unusual problems while taking this medication.

Warnings & Precautions

Before taking fostamatinib:

  • tell your doctor and pharmacist if you are allergic to fostamatinib, any other medications, or any of the ingredients in fostamatinib tablets. Ask your pharmacist for a list of the ingredients.
  • tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: clarithromycin (Biaxin, in Prevpac), digoxin (Lanoxin), itraconazole (Onmel, Sporanox), ketoconazole, rifampin (Rifadin, Rimactane, in Rifamate, in Rifater), and rosuvastatin (Crestor). Your doctor may need to change the doses of your medications or monitor you carefully for side effects. Many other medications may also interact with fostamatinib, so be sure to tell your doctor about all the medications you are taking, even those that do not appear on this list.
  • tell your doctor if you have or have ever had high blood pressure or liver disease.
  • tell your doctor if you are pregnant or plan to become pregnant. You will need to have a pregnancy test before you start treatment, and you should use birth control to prevent pregnancy during your fostamatinib treatment and for at least 1 month after your final dose. Talk to your doctor about birth control methods that you can use. If you become pregnant, call your doctor immediately. Fostamatinib may harm the fetus.
  • tell your doctor if you are breastfeeding. You should not breastfeed during your treatment with fostamatinib and for at least 1 month after your final dose.

Fostamatinib Dosage

Fostamatinib comes as a tablet to take by mouth. It is usually taken with or without food twice daily. Take fostamatinib at around the same time(s) every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take fostamatinib exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Your doctor may need to reduce, interrupt, or discontinue your treatment if you experience certain side effects or depending on your treatment response. If your number of platelets (platelet count) does not increase to a certain level after 12 weeks of treatment, your doctor may have to discontinue your treatment. Talk to your doctor about how you are feeling during your treatment.

Ask your pharmacist or doctor for a copy of the manufacturer’s information for the patient.


Keep all appointments with your doctor and the laboratory. Your doctor may order certain lab tests to check your body’s response to fostamatinib. Your doctor will also check your blood pressure regularly during your treatment with fostamatinib.

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.


All information has been provided courtesy of MedLinePlus from the National Library of Medicine and from the FDA.