The purpose of this study is to determine whether fostamatinib influences the plasma concentration of warfarin and changes its blood thinning effect, and to investigate how safe and tolerable it is when administered with warfarin.

Inclusion Criteria:

• Provision of informed consent prior to any study specific procedures (including genotyping screening sample for CYP2C9 and VKORC1).
• Males or females (of non-childbearing potential) aged 18 to 55 years (inclusive)
• Subjects must be negative for occult blood (stool card) prior to administration.
• Body weight of at least 50 kg and body mass index (BMI) between 18 and 35 kg/m2 inclusive

Exclusion Criteria:

• History of any clinically significant disease or disorder which, in the opinion of the Investigator, may put the subject at risk because of participation in the study, or influence the results of the study.
• Healthy subject predicted to be most sensitive to warfarin based on CYP2C9 and VKORC1 genotypes.
• A protein C and/or protein S deficiency.
• Absolute neutrophil count of less than 2500/mm3 or 2.5 x 109/L
• Previous treatment with warfarin for a clinical indication (ie, participation in a previous warfarin interaction study is acceptable).