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

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.