Conditions: Idiopathic Thrombocytopenic Purpura
Allocation: RANDOMIZED | Intervention model: PARALLEL
Enrollment: 24
Healthy volunteers: no

Brief summary:
Core study:

To compare the efficacy of avatrombopag (in addition to standard) of care to eltrombopag (in addition to standard of care) for the treatment of adult participants with chronic immune thrombocytopenia (idiopathic thrombocytopenic purpura \[ITP\]) as measured by durable platelet response.

Open-label Extension Phase:

To evaluate the safety and tolerability of long-term therapy with avatrombopag in participants with chronic ITP (cITP).

Detailed description:
The study consists of three phases: Prerandomization, Randomization (Core Study) and Extension Phase. Participants 18 years of age and over, who meet all the eligibility requirements will be randomized into the study. It will require that splenectomized participants make up at least 35% of the study population and no single platelet count is greater than 35x10\^9/L. Participants will be centrally stratified at randomization by splenectomy status, baseline platelet count, and use of concomitant ITP medication at baseline and randomized to receive either double-blind avatrombopag or eltrombopag in a 1:1 ratio. Participants will receive blinded therapy at a starting dose of 20 mg avatrombopag once daily or 50 mg eltrombopag once daily. Participants will be allowed to have their dose titrated up (maximum dose 40 mg avatrombopag and 75 mg for eltrombopag) or down (minimum dose 5 mg for avatrombopag and 25 mg for eltrombopag) depending on their response to study drug. The goal of dose modification is to maintain the platelet count at levels greater than or equal to 50x10\^9/L and less than or equal to 150x10\^9/L, and to decrease the need for ITP-directed concomitant medications. The duration of treatment in the Core study and the Extension Phase is approximately 26 and 104 weeks, respectively.

Arms:
arm 1: Avatrombopag will be administered orally as 5 mg, 10 mg, 20 mg, 30 mg or 40 mg in a flexible dose design for 26 weeks. Participants will receive blinded therapy at a starting dose of 20 mg avatrombopag, once daily and allow to have their dose titrated up (maximum dose of 40 mg avatrombopag) or down (minimum dose of 5 mg avatrombopag) depending on their response to study drug. arm 2: Eltrombopag will be administered orally as 25 mg, 50 mg, or 75 mg in a flexible dose design for 26 weeks. Participants will receive blinded therapy at a starting dose of 50 mg eltrombopag once daily and allow to have their dose titrated up (maximum dose of 75 mg eltrombopag) or down (minimum dose of 25 mg eltrombopag) depending on their response to study drug. arm 3: Participants who meet the eligibility requirements for the Open-label Extension (OLE) Phase or who discontinue the Core Study early because of lack of treatment effect will be eligible to continue into the OLE Phase for up to 104 weeks of open-label avatrombopag therapy. Participants who enter the OLE from the Core Study will receive a starting dose of open-label avatrombopag which will be determined by the last dose of study drug at the End of Treatment (EOT) Visit (Visit 22) of the Core Study. Participants who discontinue the Core Study early because of lack of treatment effect and enter the OLE will receive open-label avatrombopag at a starting dose of 20 mg once daily of open-label avatrombopag.

Interventions: intervention 1: Eltrombopag intervention 2: Avatrombopag intervention 3: Standard of care
Intervention descriptions: intervention 1: None intervention 2: None intervention 3: Permitted ITP concomitant background therapies are as follows:

* Corticosteroids and/or azathioprine taken at a stable dose for 4 weeks before randomization;
* Mycophenolate mofetil (MMF) or danazol taken at a stable dose for at least 12 weeks before randomization;
* Cyclosporine A (CsA) (due to the fact that it is a P-glycoprotein-mediated transport \[P-gp\] inhibitor) is to be avoided unless deemed medically necessary; CsA taken at a stable dose for at least 12 weeks before randomization.

At the discretion of the investigator, participants will be allowed to use aspirin, other salicylates, or approved adenosine diphosphate (ADP) receptor antagonists, (eg, clopidogrel, prasugrel) during the study once their platelet count had risen.

Participants treated with proton pump inhibitors (PPIs) and H2 antagonist therapy will receive a stable dose for at least 6 weeks prior to randomization. Treatment with these therapies must have been completed at least 2 weeks prior to randomization.

Protocol document: