This is a study in healthy subjects. There are two parts to the study. In the first part of the study each subject will receive a single 10mg dose of each of the four formulations of E550. Based on the results from Part 1, an optimal formulation will be selected for further evaluation in Part 2.

Inclusion Criteria:

• Healthy adult men and women (age ≥ 18 to ≤ 55 years)
• Body mass index ≥ 18.0 kg/m2 and ≤ 32.0 kg/m2 at the time of screening and baseline of Treatment Period 1
• Platelet count between 120 x 109/L and 300 x 109/L at baseline of each Treatment Period 1, 3, and 5
• Women of child bearing potential must agree to use a highly effective method of contraception, other than estrogen-based hormonal contraceptives, during the Treatment Phase of the study.

In addition, other standard criteria for healthy subjects will be used.

Exclusion Criteria:

• Evidence of clinically significant cardiovascular, hepatic, gastrointestinal, renal, respiratory, endocrine, hematologic, neurologic, or psychiatric disease or abnormalities or a known history of any gastrointestinal surgery that could impact the PK of study drug
• Agents associated with thrombotic events (including oral contraceptives) must be discontinued within 30 days of first study drug administration
• Evidence of organ dysfunction or any clinically significant event or illness in the subject's medical history, e.g., history of splenectomy.
• History of arterial or venous thrombosis, including partial or complete thrombosis (e.g., stroke, transient ischemic attack, myocardial infarction, deep vein thrombosis, or pulmonary embolism). Known family history of hereditary thrombophilic disorders (e.g., Factor V Leiden, antithrombin III deficiency, etc.)
• Hemoglobin less than the lower limit of normal levels.

In addition, other standard criteria for healthy subjects will be used.