Trial Outcomes & Findings for Evaluating the Safety and Efficacy of Romiplostim (AMG 531) in Thrombocytopenic Subjects With Immune Thrombocytopenic Purpura (ITP) (NCT NCT00111475)

NCT ID: NCT00111475

Last Updated: 2020-01-10

Results Overview

Recruitment status

COMPLETED

Study phase

PHASE2

Target enrollment

45 participants

Primary outcome timeframe

From first dose of study drug through 8 weeks (Part A) or 6 weeks (Part B) after last dose of study drug; 78 days

Results posted on

2020-01-10

Participant Flow

This study consisted of 2 parts. Part A (conducted from July 1, 2002 to October 13, 2003) was an open-label, dose-escalation trial with sequential cohorts of participants. Part B (conducted from October 6, 2003 to June 17, 2004) was a double-blind, placebo-controlled, parallel design study.

In Part A participants were sequentially assigned to escalating dose cohorts. In Part B, participants were randomized to each dose cohort; within each cohort 2 of 10 participants were randomly assigned to receive placebo. The 6.0 µg/kg dose cohort was discontinued in protocol amendment 4.

Participant milestones

Participant milestones
Measure	Part A: Romiplostim 0.2 µg/kg Participants received 0.2 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts	Part A: Romiplostim 0.5 µg/kg Participants received 0.5 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 1.0 µg/kg Participants received 1.0 µg/kg romiplostim on day 1 and on day 15 or 22 depending on platelet counts.	Part A: Romiplostim 3 µg/kg Participants received 3.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 6 µg/kg Participants received 6.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 10 µg/kg Participants received 10.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part B: Placebo Participants received placebo by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 1.0 µg/kg Participants received 1.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 3.0 µg/kg Participants received 3.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 6.0 µg/kg Participants received 6.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.
Overall Study STARTED	4	4	4	4	4	4	4	8	8	1
Overall Study COMPLETED	4	4	4	4	4	3	4	8	8	1
Overall Study NOT COMPLETED	0	0	0	0	0	1	0	0	0	0

Reasons for withdrawal

Reasons for withdrawal
Measure	Part A: Romiplostim 0.2 µg/kg Participants received 0.2 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts	Part A: Romiplostim 0.5 µg/kg Participants received 0.5 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 1.0 µg/kg Participants received 1.0 µg/kg romiplostim on day 1 and on day 15 or 22 depending on platelet counts.	Part A: Romiplostim 3 µg/kg Participants received 3.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 6 µg/kg Participants received 6.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 10 µg/kg Participants received 10.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part B: Placebo Participants received placebo by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 1.0 µg/kg Participants received 1.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 3.0 µg/kg Participants received 3.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 6.0 µg/kg Participants received 6.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.
Overall Study Lost to Follow-up	0	0	0	0	0	1	0	0	0	0

Baseline Characteristics

Part A and Part B were analyzed separately; no overall total was calculated.

Baseline characteristics by cohort

Baseline characteristics by cohort
Measure	Part A: Romiplostim 0.2 µg/kg n=4 Participants Participants received 0.2 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts	Part A: Romiplostim 0.5 µg/kg n=4 Participants Participants received 0.5 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 1.0 µg/kg n=4 Participants Participants received 1.0 µg/kg romiplostim on day 1 and on day 15 or 22 depending on platelet counts.	Part A: Romiplostim 3 µg/kg n=4 Participants Participants received 3.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 6 µg/kg n=4 Participants Participants received 6.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 10 µg/kg n=4 Participants Participants received 10.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part B: Placebo n=4 Participants Participants received placebo by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 1.0 µg/kg n=8 Participants Participants received 1.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 3.0 µg/kg n=8 Participants Participants received 3.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 6.0 µg/kg n=1 Participants Participants received 6.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Total n=45 Participants Total of all reporting groups
Age, Continuous Part A	43.5 years STANDARD_DEVIATION 15.0 • n=4 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	42.8 years STANDARD_DEVIATION 11.1 • n=4 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	42.5 years STANDARD_DEVIATION 10.7 • n=4 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	44.8 years STANDARD_DEVIATION 18.2 • n=4 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	41.3 years STANDARD_DEVIATION 14.7 • n=4 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	47.5 years STANDARD_DEVIATION 14.5 • n=4 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	—	—	—	—	43.7 years STANDARD_DEVIATION 12.8 • n=24 Participants • Part A and Part B were analyzed separately; no overall total was calculated.
Age, Continuous Part B	—	—	—	—	—	—	53.0 years STANDARD_DEVIATION 10.6 • n=4 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	43.0 years STANDARD_DEVIATION 15.0 • n=8 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	47.4 years STANDARD_DEVIATION 16.6 • n=8 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	42.0 years STANDARD_DEVIATION NA • n=1 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	14.3 years STANDARD_DEVIATION 49.0 • n=21 Participants • Part A and Part B were analyzed separately; no overall total was calculated.
Sex: Female, Male Female	3 Participants n=4 Participants	1 Participants n=4 Participants	4 Participants n=4 Participants	4 Participants n=4 Participants	3 Participants n=4 Participants	2 Participants n=4 Participants	3 Participants n=4 Participants	6 Participants n=8 Participants	5 Participants n=8 Participants	1 Participants n=1 Participants	32 Participants n=45 Participants
Sex: Female, Male Male	1 Participants n=4 Participants	3 Participants n=4 Participants	0 Participants n=4 Participants	0 Participants n=4 Participants	1 Participants n=4 Participants	2 Participants n=4 Participants	1 Participants n=4 Participants	2 Participants n=8 Participants	3 Participants n=8 Participants	0 Participants n=1 Participants	13 Participants n=45 Participants
Race/Ethnicity, Customized White	4 Participants n=4 Participants	4 Participants n=4 Participants	4 Participants n=4 Participants	4 Participants n=4 Participants	3 Participants n=4 Participants	3 Participants n=4 Participants	3 Participants n=4 Participants	5 Participants n=8 Participants	5 Participants n=8 Participants	1 Participants n=1 Participants	36 Participants n=45 Participants
Race/Ethnicity, Customized Black	0 Participants n=4 Participants	0 Participants n=4 Participants	0 Participants n=4 Participants	0 Participants n=4 Participants	1 Participants n=4 Participants	1 Participants n=4 Participants	0 Participants n=4 Participants	1 Participants n=8 Participants	0 Participants n=8 Participants	0 Participants n=1 Participants	3 Participants n=45 Participants
Race/Ethnicity, Customized Hispanic	0 Participants n=4 Participants	0 Participants n=4 Participants	0 Participants n=4 Participants	0 Participants n=4 Participants	0 Participants n=4 Participants	0 Participants n=4 Participants	1 Participants n=4 Participants	2 Participants n=8 Participants	3 Participants n=8 Participants	0 Participants n=1 Participants	6 Participants n=45 Participants
Plateleet Count Part A	10.7 1 × 10⁹ cells/L STANDARD_DEVIATION 2.70 • n=4 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	14.5 1 × 10⁹ cells/L STANDARD_DEVIATION 12.5 • n=4 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	9.06 1 × 10⁹ cells/L STANDARD_DEVIATION 4.19 • n=4 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	13.4 1 × 10⁹ cells/L STANDARD_DEVIATION 6.81 • n=4 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	12.6 1 × 10⁹ cells/L STANDARD_DEVIATION 9.00 • n=4 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	18.4 1 × 10⁹ cells/L STANDARD_DEVIATION 10.1 • n=4 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	—	—	—	—	13.1 1 × 10⁹ cells/L STANDARD_DEVIATION 7.93 • n=24 Participants • Part A and Part B were analyzed separately; no overall total was calculated.
Plateleet Count Part B	—	—	—	—	—	—	28.4 1 × 10⁹ cells/L STANDARD_DEVIATION 17.7 • n=4 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	16.9 1 × 10⁹ cells/L STANDARD_DEVIATION 7.86 • n=8 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	14.0 1 × 10⁹ cells/L STANDARD_DEVIATION 6.20 • n=8 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	15.0 1 × 10⁹ cells/L STANDARD_DEVIATION NA • n=1 Participants • Part A and Part B were analyzed separately; no overall total was calculated.	17.9 1 × 10⁹ cells/L STANDARD_DEVIATION 10.6 • n=21 Participants • Part A and Part B were analyzed separately; no overall total was calculated.

PRIMARY outcome

Timeframe: From first dose of study drug through 8 weeks (Part A) or 6 weeks (Part B) after last dose of study drug; 78 days

Population: All treated participants

Outcome measures

Outcome measures
Measure	Part A: Romiplostim 0.2 µg/kg n=4 Participants Participants received 0.2 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts	Part A: Romiplostim 0.5 µg/kg n=4 Participants Participants received 0.5 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 1.0 µg/kg n=4 Participants Participants received 1.0 µg/kg romiplostim on day 1 and on day 15 or 22 depending on platelet counts.	Part A: Romiplostim 3 µg/kg n=4 Participants Participants received 3.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 6 µg/kg n=4 Participants Participants received 6.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 10 µg/kg n=4 Participants Participants received 10.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part B: Placebo n=4 Participants Participants received placebo by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 1.0 µg/kg n=8 Participants Participants received 1.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 3.0 µg/kg n=8 Participants Participants received 3.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 6.0 µg/kg n=1 Participants Participants received 6.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.
Number of Participants With Adverse Events Deaths	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants
Number of Participants With Adverse Events Any adverse event	4 Participants	4 Participants	4 Participants	4 Participants	4 Participants	4 Participants	4 Participants	8 Participants	8 Participants	1 Participants
Number of Participants With Adverse Events Serious adverse events	2 Participants	0 Participants	0 Participants	0 Participants	0 Participants	1 Participants	2 Participants	0 Participants	1 Participants	0 Participants
Number of Participants With Adverse Events Treatment-related adverse events	0 Participants	0 Participants	3 Participants	0 Participants	1 Participants	1 Participants	1 Participants	2 Participants	4 Participants	0 Participants
Number of Participants With Adverse Events Treatment-related serious adverse events	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	1 Participants	0 Participants	0 Participants	1 Participants	0 Participants
Number of Participants With Adverse Events Discontinuations due to adverse events	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants

PRIMARY outcome

Timeframe: Assessed on day 29 (Part A only), day 43 (Part B only), and day 78

Population: All treated participants

The development of antibodies to romiplostim or to endogenous thrombopoietin (eTPO) was assessed using a neutralizing bioassay. Participants positive for neutralizing antibodies at any of the assessments during the study are reported.

Outcome measures

Outcome measures
Measure	Part A: Romiplostim 0.2 µg/kg n=4 Participants Participants received 0.2 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts	Part A: Romiplostim 0.5 µg/kg n=4 Participants Participants received 0.5 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 1.0 µg/kg n=4 Participants Participants received 1.0 µg/kg romiplostim on day 1 and on day 15 or 22 depending on platelet counts.	Part A: Romiplostim 3 µg/kg n=4 Participants Participants received 3.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 6 µg/kg n=4 Participants Participants received 6.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 10 µg/kg n=4 Participants Participants received 10.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part B: Placebo n=4 Participants Participants received placebo by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 1.0 µg/kg n=8 Participants Participants received 1.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 3.0 µg/kg n=8 Participants Participants received 3.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 6.0 µg/kg n=1 Participants Participants received 6.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.
Number of Participants With Anti-romiplostim or Anti-endogenous Thrombopoietin Neutralizing Antibodies Anti-romiplostim neutralizing antibodies	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants
Number of Participants With Anti-romiplostim or Anti-endogenous Thrombopoietin Neutralizing Antibodies Anti-eTPO neutralizing antibodies	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants

SECONDARY outcome

Timeframe: After first dose (day 1 to day 15 or 22) and after second dose (day 15 or 22 to day 78)

Population: Participants enrolled in Part A who received each dose of romiplostim.

Targeted therapeutic platelet level was defined as a doubling of baseline platelet counts and between 50 to 450 x 10⁹ cells/L. Platelet count data after the use of rescue medication were not included; participants with no platelet count data were considered non-responders.

Outcome measures

Outcome measures
Measure	Part A: Romiplostim 0.2 µg/kg n=4 Participants Participants received 0.2 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts	Part A: Romiplostim 0.5 µg/kg n=4 Participants Participants received 0.5 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 1.0 µg/kg n=4 Participants Participants received 1.0 µg/kg romiplostim on day 1 and on day 15 or 22 depending on platelet counts.	Part A: Romiplostim 3 µg/kg n=4 Participants Participants received 3.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 6 µg/kg n=4 Participants Participants received 6.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 10 µg/kg n=4 Participants Participants received 10.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part B: Placebo Participants received placebo by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 1.0 µg/kg Participants received 1.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 3.0 µg/kg Participants received 3.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 6.0 µg/kg Participants received 6.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.
Number of Participants Who Achieved Targeted Therapeutic Platelet Level in Part A After first dose	1 Participants	0 Participants	0 Participants	1 Participants	1 Participants	1 Participants	—	—	—	—
Number of Participants Who Achieved Targeted Therapeutic Platelet Level in Part A After second dose	1 Participants	0 Participants	0 Participants	2 Participants	1 Participants	1 Participants	—	—	—	—
Number of Participants Who Achieved Targeted Therapeutic Platelet Level in Part A After both doses	1 Participants	0 Participants	0 Participants	1 Participants	1 Participants	1 Participants	—	—	—	—

SECONDARY outcome

Timeframe: After first dose (day 1 to day 15 or 22), and after second dose (day 15 or 22 to day 78)

Population: Participants enrolled in Part A who received each dose of romiplostim

Platelet count data after the use of rescue medication were not included; participants with no platelet count data were considered non-responders.

Outcome measures

Outcome measures
Measure	Part A: Romiplostim 0.2 µg/kg n=4 Participants Participants received 0.2 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts	Part A: Romiplostim 0.5 µg/kg n=4 Participants Participants received 0.5 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 1.0 µg/kg n=4 Participants Participants received 1.0 µg/kg romiplostim on day 1 and on day 15 or 22 depending on platelet counts.	Part A: Romiplostim 3 µg/kg n=4 Participants Participants received 3.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 6 µg/kg n=4 Participants Participants received 6.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 10 µg/kg n=4 Participants Participants received 10.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part B: Placebo Participants received placebo by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 1.0 µg/kg Participants received 1.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 3.0 µg/kg Participants received 3.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 6.0 µg/kg Participants received 6.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.
Number of Participants With an Increase in Platelet Count of ≥ 20 x 10⁹ Cells/L Over Baseline in Part A After first dose	1 Participants	1 Participants	1 Participants	2 Participants	2 Participants	3 Participants	—	—	—	—
Number of Participants With an Increase in Platelet Count of ≥ 20 x 10⁹ Cells/L Over Baseline in Part A After second dose	1 Participants	0 Participants	0 Participants	3 Participants	1 Participants	1 Participants	—	—	—	—
Number of Participants With an Increase in Platelet Count of ≥ 20 x 10⁹ Cells/L Over Baseline in Part A After both doses	1 Participants	0 Participants	0 Participants	2 Participants	1 Participants	1 Participants	—	—	—	—

SECONDARY outcome

Timeframe: After first dose (day 1 to day 15 or 22) and after second dose (day 15 or 22 to day 78)

Population: Participants enrolled in Part A who received each dose of romiplostim

Platelet count data after the use of rescue medication were not included; participants with no platelet count data were considered non-responders.

Outcome measures

Outcome measures
Measure	Part A: Romiplostim 0.2 µg/kg n=4 Participants Participants received 0.2 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts	Part A: Romiplostim 0.5 µg/kg n=4 Participants Participants received 0.5 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 1.0 µg/kg n=4 Participants Participants received 1.0 µg/kg romiplostim on day 1 and on day 15 or 22 depending on platelet counts.	Part A: Romiplostim 3 µg/kg n=4 Participants Participants received 3.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 6 µg/kg n=4 Participants Participants received 6.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 10 µg/kg n=4 Participants Participants received 10.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part B: Placebo Participants received placebo by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 1.0 µg/kg Participants received 1.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 3.0 µg/kg Participants received 3.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 6.0 µg/kg Participants received 6.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.
Number of Participants With a Peak Platelet Count ≥ 100 x 10⁹ Cells/L in Part A After first dose	1 Participants	0 Participants	0 Participants	1 Participants	2 Participants	3 Participants	—	—	—	—
Number of Participants With a Peak Platelet Count ≥ 100 x 10⁹ Cells/L in Part A After second dose	0 Participants	0 Participants	0 Participants	2 Participants	1 Participants	1 Participants	—	—	—	—
Number of Participants With a Peak Platelet Count ≥ 100 x 10⁹ Cells/L in Part A After both doses	0 Participants	0 Participants	0 Participants	1 Participants	1 Participants	1 Participants	—	—	—	—

SECONDARY outcome

Timeframe: After first dose (day 1 to day 15 or 22) and after second dose (day 15 or 22 to day 78)

Population: Participants enrolled in Part A who received each dose of romiplostim

Platelet count data after the use of rescue medication were not included; participants with no platelet count data were considered non-responders.

Outcome measures

Outcome measures
Measure	Part A: Romiplostim 0.2 µg/kg n=4 Participants Participants received 0.2 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts	Part A: Romiplostim 0.5 µg/kg n=4 Participants Participants received 0.5 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 1.0 µg/kg n=4 Participants Participants received 1.0 µg/kg romiplostim on day 1 and on day 15 or 22 depending on platelet counts.	Part A: Romiplostim 3 µg/kg n=4 Participants Participants received 3.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 6 µg/kg n=4 Participants Participants received 6.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 10 µg/kg n=4 Participants Participants received 10.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part B: Placebo Participants received placebo by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 1.0 µg/kg Participants received 1.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 3.0 µg/kg Participants received 3.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 6.0 µg/kg Participants received 6.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.
Number of Participants With a Peak Platelet Count of > 450 x 10⁹ Cells/L in Part A After first dose	0 Participants	0 Participants	0 Participants	0 Participants	1 Participants	2 Participants	—	—	—	—
Number of Participants With a Peak Platelet Count of > 450 x 10⁹ Cells/L in Part A After second dose	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	—	—	—	—
Number of Participants With a Peak Platelet Count of > 450 x 10⁹ Cells/L in Part A After both doses	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	—	—	—	—

SECONDARY outcome

Timeframe: After first dose (day 1 to day 15 or 22) and after second dose (day 15 or 22 to day 78)

Population: Participants enrolled in Part A who received each dose of romiplostim and with a platelet count of ≥ 50 × 10⁹ cells/L and a doubling of the baseline platelet count, in the absence of rescue medication.

Platelet count data after the use of rescue medication were not included.

Outcome measures

Outcome measures
Measure	Part A: Romiplostim 0.2 µg/kg n=1 Participants Participants received 0.2 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts	Part A: Romiplostim 0.5 µg/kg Participants received 0.5 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 1.0 µg/kg Participants received 1.0 µg/kg romiplostim on day 1 and on day 15 or 22 depending on platelet counts.	Part A: Romiplostim 3 µg/kg n=2 Participants Participants received 3.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 6 µg/kg n=2 Participants Participants received 6.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 10 µg/kg n=3 Participants Participants received 10.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part B: Placebo Participants received placebo by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 1.0 µg/kg Participants received 1.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 3.0 µg/kg Participants received 3.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 6.0 µg/kg Participants received 6.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.
Peak Platelet Count After Each Dose in Part A After first dose	123.0 1 × 10⁹ cells/L	—	—	163.0 1 × 10⁹ cells/L	309.0 1 × 10⁹ cells/L Standard Deviation 202.2	746.3 1 × 10⁹ cells/L Standard Deviation 611.9	—	—	—	—
Peak Platelet Count After Each Dose in Part A After second dose	65.0 1 × 10⁹ cells/L	—	—	140.5 1 × 10⁹ cells/L Standard Deviation 29.0	244.0 1 × 10⁹ cells/L	259.0 1 × 10⁹ cells/L	—	—	—	—

SECONDARY outcome

Timeframe: Baseline and after first dose (day 1 to day 15 or 22) and after second dose (day 15 or 22 to day 78)

Platelet count data after the use of rescue medication were not included.

Outcome measures

Outcome measures
Measure	Part A: Romiplostim 0.2 µg/kg n=1 Participants Participants received 0.2 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts	Part A: Romiplostim 0.5 µg/kg Participants received 0.5 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 1.0 µg/kg Participants received 1.0 µg/kg romiplostim on day 1 and on day 15 or 22 depending on platelet counts.	Part A: Romiplostim 3 µg/kg n=2 Participants Participants received 3.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 6 µg/kg n=2 Participants Participants received 6.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 10 µg/kg n=3 Participants Participants received 10.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part B: Placebo Participants received placebo by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 1.0 µg/kg Participants received 1.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 3.0 µg/kg Participants received 3.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 6.0 µg/kg Participants received 6.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.
Change From Baseline in Peak Platelet Count After Each Dose in Part A After first dose	109.5 1 × 10⁹ cells/L	—	—	150.2 1 × 10⁹ cells/L	289.3 1 × 10⁹ cells/L Standard Deviation 208.2	725.5 1 × 10⁹ cells/L Standard Deviation 622.5	—	—	—	—
Change From Baseline in Peak Platelet Count After Each Dose in Part A After second dose	51.50 1 × 10⁹ cells/L	—	—	122.6 1 × 10⁹ cells/L Standard Deviation 21.78	220.0 1 × 10⁹ cells/L	231.7 1 × 10⁹ cells/L	—	—	—	—

SECONDARY outcome

Timeframe: After first dose (day 1 to day 15 or 22) and after second dose (day 15 or 22 to day 78)

Platelet count data after the use of rescue medication were not included.

Outcome measures

Outcome measures
Measure	Part A: Romiplostim 0.2 µg/kg n=1 Participants Participants received 0.2 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts	Part A: Romiplostim 0.5 µg/kg Participants received 0.5 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 1.0 µg/kg Participants received 1.0 µg/kg romiplostim on day 1 and on day 15 or 22 depending on platelet counts.	Part A: Romiplostim 3 µg/kg n=2 Participants Participants received 3.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 6 µg/kg n=2 Participants Participants received 6.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part A: Romiplostim 10 µg/kg n=3 Participants Participants received 10.0 µg/kg romiplostim on day 1 and day 15 or 22, depending on platelet counts.	Part B: Placebo Participants received placebo by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 1.0 µg/kg Participants received 1.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 3.0 µg/kg Participants received 3.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.	Part B: Romiplostim 6.0 µg/kg Participants received 6.0 µg/kg romiplostim by subcutaneous injection once a week for 6 weeks.
Time to Peak Platelet Count After Each Dose in Part A After second dose	10.0 days Interval 10.0 to 10.0	—	—	11.0 days Interval 9.0 to 13.0	10.0 days Interval 10.0 to 10.0	11.0 days Interval 11.0 to 11.0	—	—	—	—
Time to Peak Platelet Count After Each Dose in Part A After first dose	10.0 days Interval 10.0 to 10.0	—	—	11.0 days Interval 11.0 to 11.0	9.5 days Interval 8.0 to 11.0	15.0 days Interval 12.0 to 15.0	—	—	—	—

SECONDARY outcome

Timeframe: After first dose (day 1 to day 15 or 22) and after second dose (day 15 or 22 to day 78)

Population: Participants enrolled in Part A who received each dose of romiplostim and with a platelet count ≥ 50 × 10⁹ cells/L and ≤ 450 × 10⁹ cells/L and a doubling of the baseline platelet count, in the absence of rescue medication.

Targeted therapeutic platelet level was defined as a platelet count that was double the baseline level and ≥ 50 and ≤ 450 × 10⁹ cells/L. Platelet count data after the use of rescue medication were not included.