Fostamatinib

Fostamatinib is a prescription medication indicated for the treatment of thrombocytopenia in adult patients with chronic immune thrombocytopenia (ITP) who have had an insufficient response to a previous treatment.

• Fostamatinib is available under the following different brand names: Tavalisse

Common side effects of Fostamatinib include:

• diarrhea
• high blood pressure (hypertension)
• nausea
• respiratory infection
• dizziness
• increased ALT/AST
• rash
• abdominal pain
• fatigue
• chest pain and low white blood cell count (neutropenia)

Serious side effects of Fostamatinib include:

• 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

Rare side effects of Fostamatinib include:

• none

Seek medical care or call 911 at once if you have the following serious side effects:

• Severe headache, confusion, slurred speech, arm or leg weakness, trouble walking, coordination loss, unsteady, very stiff muscles, high fever, profuse sweating, or tremors.
• Serious eye symptoms such as sudden vision loss, blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights.
• Serious heart symptoms include fast, irregular, or pounding heartbeats; fluttering in the chest; shortness of breath; sudden dizziness, lightheadedness, or passing out.

This is not a complete list of side effects and other serious side effects or health problems that may occur because of the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may report side effects or health problems to FDA at 1-800-FDA-1088.

Adult dosage

Tablet

• 100 mg
• 150 mg

Immune Thrombocytopenia 

Adult dosage

• Initial dose: 100 mg orally two times a day
• After a month, if the platelet count has not increased to at least 50 × 10^9/L, increase the dose to 150 mg orally two times a day
• Use the lowest dose to achieve and maintain a platelet count of at least 50 × 10^9/L as necessary to reduce the risk of bleeding

Dosage Considerations – Should be Given as Follows:

• See “Dosages”

If your medical doctor is using this medicine to treat your pain, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider, or pharmacist first.

• Fostamatinib has severe interactions with the following drug:
  • lonafarnib
• Fostamatinib has serious interactions with at least 49 other drugs.
• Fostamatinib has moderate interactions with at least 132 other drugs.
• Fostamatinib has minor interactions with the following drugs:
  • acetazolamide
  • anastrozole
  • cyclophosphamide
  • larotrectinib
  • voclosporin

This information does not contain all possible interactions or adverse effects. Visit the RxList Drug Interaction Checker for any drug interactions. Therefore, before using this product, tell your doctor or pharmacist about all the products you use. Keep a list of all your medications with you and share this information with your doctor and pharmacist. Check with your healthcare professional or doctor for additional medical advice, health questions, or concerns.

Contraindications

• None

Effects of drug abuse

• None

Short-Term Effects

• See “What Are Side Effects Associated with Using Fostamatinib?”

Long-Term Effects

• See “What Are Side Effects Associated with Using Fostamatinib?”

Cautions

• Hypertension can occur, including hypertensive crisis; patients with preexisting hypertension may be more susceptible; monitor blood pressure every 2 weeks until stable, then monthly, and adjust or initiate antihypertensive therapy for control
• Elevated LFTs (mainly ALT and AST) reported; transaminases typically recover to baseline levels within 2-6 weeks of dose-modification; monitor liver function tests monthly during treatment; monitor liver function tests monthly during treatment; if ALT or AST levels increase more than 3 × ULN, manage hepatotoxicity by interruption, reduction, or discontinuation of therapy
• Diarrhea occurs commonly; use supportive care measures (eg, dietary changes, hydration, and/or antidiarrheal medication) early after the onset of symptoms; monitor patients for the development of diarrhea; if diarrhea becomes severe (Grade 3 and above), consider interruption, reduction, or discontinuation of therapy
• Neutropenia reported, including cases of febrile neutropenia; monitor ANC monthly and for infection during treatment; manage toxicity with therapy interruption, dose reduction, or discontinuation.
• Based on findings from animal studies and the drug’s mechanism of action, it can cause fetal harm when administered to pregnant women
• Drug interaction overview
  • Effect of other drugs on fostamatinib
    • Strong CYP3A4 inhibitors: Coadministration increases exposure to R406 (the major active metabolite), which may increase the risk of adverse reactions; fostamatinib dose reduction may be required
    • Strong CYP3A4 inducers: Coadministration is not recommended owing to reduced exposure to R406
  • Effect of Fostamatinib on other drugs
    • CYP3A4, BCRP, and/or P-gp substrates: Coadministration with Fostamatinib may increase concentrations of some substrate drugs; substrate drugs may require dose reduction

Pregnancy and Lactation

• There are no available data on pregnant women to inform the drug-associated risk
• In animal reproduction studies, administration of Fostamatinib to pregnant rats and rabbits during organogenesis caused adverse developmental outcomes, which were directly attributed to exposure in utero to R406 at maternal exposures (AUC) as low as 0.3 and 10 times the exposure in patients at the maximum recommended human dose, respectively
• Verify pregnancy status in women with reproductive potential before initiating fostamatinib; advise pregnant women of the potential risk to a fetus
• Fertility
  • There are no data on the effect of fostamatinib on human fertility
  • Based on the finding of reduced pregnancy rates in animal studies, fostamatinib may affect women’s fertility
• Contraception
  • Women should use effective contraception during treatment and for at least 1 month after the last dose of fostamatinib
• Lactation
  • Unknown if fostamatinib is distributed in human breast milk
  • In rodents, R406 was detected in maternal milk in concentrations 5- to 10-fold higher than in maternal plasma
  • Advise a lactating woman not to breastfeed during treatment with fostamatinib and for at least 1 month after the last dose
  • Consider the developmental and health benefits of breastfeeding along with the mother’s clinical need for the drug, and any potential adverse effects on the breastfed infant from the drug or the underlying maternal condition