List of products in the National Drug Code with proprietary name . This medication is used to treat people with a certain blood disorder known as chronic immune thrombocytopenia-ITP. This is a condition where the amount of one type of cell in your blood (platelets) is lower than normal. ITP can lead to serious bleeding problems. Fostamatinib belongs to a class of drugs known as spleen tyrosine kinase inhibitors. It works by increasing platelets in your blood.