Combination Therapy of Romiplostim and Erythropoiesis-stimulating Agents

The goal of this Phase 2 clinical trial is to learn if adding romiplostim to standard erythropoiesis-stimulating agent (ESA) therapy is safe and tolerated in adults with chronic kidney disease who are on hemodialysis and have anemia that has not responded well to ESAs. The study will mainly check platelet counts and side effects. The main questions it aims to answer are: How many participants keep platelet counts within a normal range during and after treatment? How many participants have platelet counts that rise above the normal range? What medical problems or side effects occur after romiplostim is added to ESA therapy? Researchers will study three dose levels of romiplostim (0.2, 0.5, and 1 mg/kg) in small groups of participants. There is no placebo group. All participants will receive romiplostim plus their usual ESA and iron supplement. The study will also measure changes in hemoglobin and iron-related blood markers. Participants will: Receive romiplostim as an injection under the skin once weekly for 3 weeks. Each participant will be assigned to one of three dose groups. Continue their usual ESA therapy (darbepoetin or Mircera) and iron supplement. Have blood tests to check platelet counts, hemoglobin, and other blood and iron measures. Blood tests will be frequent at first and then less often. Visit the clinic regularly for up to 24 weeks, with a follow-up visit about 4 weeks after the end-of-treatment visit. Have other safety checks, such as vital signs, physical exams, and electrocardiograms (ECGs).

Inclusion Criteria: 1. Previously failed treatment with erythropoiesis-stimulating agents (ESAs) or had a poor response to ESAs. ESA resistance is defined as: * Transfusion-dependent patients requiring a minimum dose of \>=40,000 units of epoetin alfa/week for 8 weeks, or an equivalent dose of darbepoetin alfa (1.5 mg/kg/week or 120 mg every 2 weeks) or Mircera (100 mg every 2 weeks) for 8 weeks, with failure to achieve transfusion independence; OR * Non-transfusion-dependent patients who fail to achieve a \>=2 g increase in hemoglobin (Hgb) level sustained for \>=4 weeks. 2. Male or female subjects at least 18 years of age. 3. Currently receiving darbepoetin or Mircera for anemia and iron supplement. 4. Receiving chronic maintenance hemodialysis for end-stage kidney disease. Note: Only hemodialysis patients will be enrolled because frequent blood sampling is required. 5. Having symptomatic anemia without transfusion and with Hgb levels \