Platelet counts and romiplostim doses by study week. (A) Median (25th [Q1] and 75th [Q3] percentiles) platelet counts by study week. In the romiplostim group, the median weekly platelet count increased with time on study and was near or > 50 × 10⁹/L after 6 weeks of treatment, whereas the counts in placebo group remained at or near 10 × 10⁹/L. Platelet counts within 4 weeks of administration of rescue medication were excluded. (B) Median (25th [Q1] and 75th [Q3] percentiles) weekly doses of romiplostim and placebo administered during the study. The dose of romiplostim increased slowly though week7 and then remained stable at approximately 5 μg/kg. The dose of placebo increased steadily throughout the treatment period. The median romiplostim dose decreased after the start of the pharmacokinetics assessment period because the 2 patients who did not respond to romiplostim did not enter this phase of the trial. Both nonresponding patients had been receiving romiplostim at 10 μg/kg at week 12.