Phase 2, Parallel Group, Rollover Study of AKR-501 in Patients With ChronicITP Who Completed 28 Days of Study Treatment in Protocol 501-CL-003

The purpose of this study is to determine the safety and efficacy of AKR-501 (avatrombopag) administered in participants with chronic Idiopathic Thrombocytopenic Purpura (ITP) who were enrolled into and completed 28 days of study treatment in Protocol 501-CL-003 (NCT00441090).

Participants eligible to enroll into this rollover protocol will begin study treatment within 2-5 days of their Day 28 study termination visit in Protocol 501-CL-003 (NCT00441090). Participants who met the primary efficacy response criterion in Protocol 501-CL-003 will continue receiving the same study treatment to which they were assigned in the previous protocol in a double-blinded manner, these being one of the following 5 treatments:

* avatrombopag 2.5 mg daily
* avatrombopag 5 mg daily
* avatrombopag 10 mg daily
* avatrombopag 20 mg daily
* placebo

Participants who did not meet the primary efficacy response criterion in Protocol 501-CL-003 who otherwise meet the eligibility criteria for this rollover protocol will be offered open label avatrombopag 10 mg daily.

This is a parallel group, rollover study.

Eligibility Criteria:
Inclusion Criteria:

1. Patients who completed 28 days of study treatment in Protocol 501-CL-003.
2. No significant safety or tolerability concerns from the patient's participation of Protocol 501-CL-003 as determined by the Investigator.
3. Received medical monitor approval for enrollment into this study.
4. Patients receiving maintenance corticosteroids may be enrolled, as long as the corticosteroids have been administered at a stable dose and the Investigator does not foresee the need to change the steroid dose during study participation. Patients should remain on this stable corticosteroid dose during study participation.
5. Women of child-bearing potential must have a negative serum pregnancy test at the Day 28 assessment in Protocol 501-CL-003. (Childbearing potential is defined as any woman who has not been surgically sterilized and is pre-menopausal or peri-menopausal i.e., any menstrual flow within 12 months of Screening Visit A for Protocol 501-CL-003).
6. Women of child-bearing potential must agree to practice a medically approved form of contraception (one of the following must be used: condoms (male or female) with a spermicidal agent, diaphragm or cervical cap with a spermicidal agent, IUD,hormonal contraception, abstinence).
7. Willing and able to provide written informed consent.

Exclusion Criteria:

1. Women who are pregnant and/or lactating.
2. Use of the following drugs or treatments:

   * Rituximab
   * Azathioprine, Cyclosporine A, or other immunosuppressant therapy
   * Aspirin, Aspirin-containing compounds, Salicylates,Anticoagulants, Non-steroidal anti-inflammatory drugs(NSAIDs)(including Cyclooxygenase-2 \[COX-2\] specific NSAIDs), clopidogrel; ticlopidine; and any drugs that affect platelet function.
   * Danazol
   * Rh0(D) immune globulin (WinRho®) or intravenous immunoglobulin (IVIG).
3. Inability to comply with protocol requirements or give informed consent, as determined by the Investigator.

For more information regarding inclusion/exclusion criteria, please see record for AKR 501-CL-003 Protocol.