Part B participants received romiplostim 750 µg subcutaneously every two weeks (Q2W) for 8 weeks. Participants who complete Part B could continue to receive injections of romiplostim for up to 1 year in the extension treatment phase.

Part B participants received romiplostim 750 µg intravenously (IV) once every two weeks for 8 weeks. Participants who complete Part B could continue to receive romiplostim for up to 1 year in the extension treatment phase.

Participants with a complete or major response during the treatment phase. A complete platelet response was defined as a platelet count ≥ 100 x 10^9/L during the treatment phase. A major platelet response was defined as an increase in absolute platelet count of ≥ 30 x 10^9/L for patients starting with > 20 x 10^9/L platelets, or an increase from ≤ 20 x 10^9/L to > 20 x 10^9/L and by at least 100%. Any participant receiving rescue medication was considered a non-responder. Platelet transfusions were considered rescue medication.

The number of participants with a platelet response according to the modified International Working Group (IWG) criteria. Response was defined as an absolute increase of ≥ 30 x 10^9/L with Baseline platelet count > 20 x 10^9/L, or with a Baseline count ≤ 20 x 10^9/L, increasing to above 20 x 10^9/L and by at least 100% during the treatment or extension period and maintained for at least 8 consecutive weeks. Platelet transfusion was not considered a rescue medication but platelet counts ≤72 hours after platelet transfusion were excluded from the analysis.

The number of participants with a platelet response according to the modified International Working Group (IWG) criteria. Response was defined as an absolute increase of ≥ 30 x 10^9/L with Baseline platelet count > 20 x 10^9/L, or with a Baseline count ≤ 20 x 10^9/L, increasing to above 20 x 10^9/L and by at least 100% during the treatment or extension period and maintained for at least 8 consecutive weeks. Platelet transfusion was not considered a rescue medication but platelet counts ≤72 hours after platelet transfusion were excluded from the analysis.

Peak platelet count (10^9/L) during the treatment period.

Participants achieving first platelet response according to IWG criteria, by study week. Platelet response was defined as an absolute increase of ≥ 30 x 10^9/L with Baseline platelet count > 20 x 10^9/L, or with a Baseline ≤ 20 x 10^9/L increasing the platelet count to above 20 x 10^9/L and by at least 100% for 8 consecutive weeks. Platelet counts obtained within 72 hours of platelet transfusion were not evaluable for platelet response.

Duration of platelet response per IWG criteria (absolute increase of ≥ 30 x 10^9/L with Baseline platelet count > 20 x 10^9/L, or with a Baseline ≤ 20 x 10^9/L increasing the platelet count to above 20 x 10^9/L and by at least 100% for 8 consecutive weeks).

Maximum observed serum concentration (Cmax) of romiplostim during Week 1

Measured romiplostim concentration at the end of the week 1 dosing interval (Ctrough)

Area under the romiplostim concentration-time curve from time zero to the last time point with quantifiable concentration (AUC0-4) during Week 1

Maximum observed serum concentration (Cmax) of romiplostim during Week 7.

Measured romiplostim concentration at the end of the Week 7 dosing interval (Ctrough)

Area under the romiplostim concentration-time curve from time zero to the last time point with quantifiable concentration (AUC0-4) during Week 7.

Time at which the maximum concentration of romiplostum was observed after subcutaneous administration during Week 1

Time at which the maximum concentration of romiplostum was observed after subcutaneous administration during Week 7

Cohort 3 in Part A, participants received romiplostim 1000 µg subcutaneously once weekly for up to 3 weeks. Participants who completed Part A could continue to receive weekly injections of romiplostim for up to 1 year in the extension treatment phase.

Cohort 4 in Part A, participants received romiplostim 1500 µg subcutaneously once weekly for up to 3 weeks. Participants who completed Part A could continue to receive weekly injections of romiplostim for up to 1 year in the extension treatment phase.

Part B participants received romiplostim 750 µg subcutaneously (SC) once weekly (QW) for 8 weeks. Participants who completed Part B could continue to receive weekly injections of romiplostim for up to 1 year in the extension treatment phase.

Part B participants received romiplostim 750 µg subcutaneously every two weeks (Q2W) for 8 weeks. Participants who completed Part B could continue to receive injections of romiplostim for up to 1 year in the extension treatment phase.

Part B participants received romiplostim 750 µg intravenously (IV) once every two weeks for 8 weeks. Participants who completed Part B could continue to receive romiplostim for up to 1 year in the extension treatment phase.

Total of all reporting groups

Cohort 2 in Part A, participants received romiplostim 700 µg subcutaneously once weekly for up to 3 weeks. Participants who completed Part A could continue to receive weekly injections of romiplostim for up to 1 year in the extension treatment phase.

Cohort 3 in Part A, participants received romiplostim 1000 µg subcutaneously once weekly for up to 3 weeks. Participants who completed Part A could continue to receive weekly injections of romiplostim for up to 1 year in the extension treatment phase.

Cohort 4 in Part A, participants received romiplostim 1500 µg subcutaneously once weekly for up to 3 weeks. Participants who completed Part A could continue to receive weekly injections of romiplostim for up to 1 year in the extension treatment phase.

Participants with a complete or major response during the treatment phase. A complete platelet response was defined as a platelet count ≥ 100 x 10^9/L during the treatment phase. A major platelet response was defined as an increase in absolute platelet count of ≥ 30 x 10^9/L for patients starting with > 20 x 10^9/L platelets, or an increase from ≤ 20 x 10^9/L to > 20 x 10^9/L and by at least 100%. Any participant receiving rescue medication was considered a non-responder. Platelet transfusions were considered rescue medication.

Efficacy Analysis Set, composed of all enrolled participants who received romiplostim and completed the treatment phase.

The number of participants with a platelet response according to the modified International Working Group (IWG) criteria. Response was defined as an absolute increase of ≥ 30 x 10^9/L with Baseline platelet count > 20 x 10^9/L, or with a Baseline count ≤ 20 x 10^9/L, increasing to above 20 x 10^9/L and by at least 100% during the treatment or extension period and maintained for at least 8 consecutive weeks. Platelet transfusion was not considered a rescue medication but platelet counts ≤72 hours after platelet transfusion were excluded from the analysis.

Subset of Efficacy Analysis Set, composed of all enrolled participants who received romiplostim and completed the treatment phase, who entered the treatment extension.

The number of participants with a platelet response according to the modified International Working Group (IWG) criteria. Response was defined as an absolute increase of ≥ 30 x 10^9/L with Baseline platelet count > 20 x 10^9/L, or with a Baseline count ≤ 20 x 10^9/L, increasing to above 20 x 10^9/L and by at least 100% during the treatment or extension period and maintained for at least 8 consecutive weeks. Platelet transfusion was not considered a rescue medication but platelet counts ≤72 hours after platelet transfusion were excluded from the analysis.

Efficacy Analysis Set, composed of all enrolled participants who received romiplostim and completed the treatment phase

Peak platelet count (10^9/L) during the treatment period.

Efficacy Analysis Set, composed of all enrolled participants who received romiplostim and completed the treatment phase.

Participants achieving first platelet response according to IWG criteria, by study week. Platelet response was defined as an absolute increase of ≥ 30 x 10^9/L with Baseline platelet count > 20 x 10^9/L, or with a Baseline ≤ 20 x 10^9/L increasing the platelet count to above 20 x 10^9/L and by at least 100% for 8 consecutive weeks. Platelet counts obtained within 72 hours of platelet transfusion were not evaluable for platelet response.

Efficacy Analysis Set, composed of all enrolled participants who received romiplostim and completed the treatment phase

Duration of platelet response per IWG criteria (absolute increase of ≥ 30 x 10^9/L with Baseline platelet count > 20 x 10^9/L, or with a Baseline ≤ 20 x 10^9/L increasing the platelet count to above 20 x 10^9/L and by at least 100% for 8 consecutive weeks).

Subset of Efficacy Analysis Set, composed of all enrolled participants who received romiplostim and completed the treatment phase, who had a platelet response

Maximum observed serum concentration (Cmax) of romiplostim during Week 1

Safety Analysis Set, composed of all enrolled participants who received at least one dose of romiplostim

Measured romiplostim concentration at the end of the week 1 dosing interval (Ctrough)

Safety Analysis Set, composed of all enrolled participants who received at least one dose of romiplostim

Area under the romiplostim concentration-time curve from time zero to the last time point with quantifiable concentration (AUC0-4) during Week 1

Safety Analysis Set, composed of all enrolled participants who received at least one dose of romiplostim

Maximum observed serum concentration (Cmax) of romiplostim during Week 7.

Safety Analysis Set, composed of all enrolled participants who received at least one dose of romiplostim

Measured romiplostim concentration at the end of the Week 7 dosing interval (Ctrough)

Safety Analysis Set, composed of all enrolled participants who received at least one dose of romiplostim

Area under the romiplostim concentration-time curve from time zero to the last time point with quantifiable concentration (AUC0-4) during Week 7.

Safety Analysis Set, composed of all enrolled participants who received at least one dose of romiplostim

Time at which the maximum concentration of romiplostum was observed after subcutaneous administration during Week 1

Safety Analysis Set, composed of all enrolled participants who received at least one dose of romiplostim

Time at which the maximum concentration of romiplostum was observed after subcutaneous administration during Week 7

Safety Analysis Set, composed of all enrolled participants who received at least one dose of romiplostim

The number of participants experiencing one or more adverse events during the treatment phase or extension phase of Part A.

All participants who received at least one dose of study medication

The number of participants experiencing one or more adverse events during the treatment phase or extension phase of Part B.

All participants who received at least one dose of study medication

Cohort 2 in Part A, participants received romiplostim 700 µg subcutaneously once weekly for up to 3 weeks. Participants who completed Part A could continue to receive weekly injections of romiplostim for up to 1 year in the extension treatment phase.

Cohort 3 in Part A, participants received romiplostim 1000 µg subcutaneously once weekly for up to 3 weeks. Participants who completed Part A could continue to receive weekly injections of romiplostim for up to 1 year in the extension treatment phase.

Cohort 4 in Part A, participants received romiplostim 1500 µg subcutaneously once weekly for up to 3 weeks. Participants who completed Part A could continue to receive weekly injections of romiplostim for up to 1 year in the extension treatment phase.

Part B participants received romiplostim 750 µg subcutaneously (SC) once weekly (QW) for 8 weeks. Participants who completed Part B could continue to receive weekly injections of romiplostim for up to 1 year in the extension treatment phase.

Part B participants received romiplostim 750 µg subcutaneously every two weeks (Q2W) for 8 weeks. Participants who completed Part B could continue to receive injections of romiplostim for up to 1 year in the extension treatment phase.

Part B participants received romiplostim 750 µg intravenously (IV) once every two weeks for 8 weeks. Participants who completed Part B could continue to receive romiplostim for up to 1 year in the extension treatment phase.