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Novel Agent Sustains Platelet Counts in Splenectomized Patients With Chronic ITP: Presented at ASH

By Sophie Bainbridge

ATLANTA, GA -- December 9, 2007 -- The experimental agent romiplostim increased platelet counts and maintained that increase over 24 weeks in splenectomized patients with chronic immune thrombocytopenic purpura (ITP), according to a phase 3, placebo-controlled trial presented here at the 49th American Society of Hematology (ASH) Annual Meeting and Exposition.

Romiplostin (AMG 531) was well tolerated and patients who received it required fewer rescue medications compared with those receiving placebo, according to Terry B. Gernsheimer, MD, Associate Professor of Medicine, Division of Hematology, University of Washington, and Director of Transfusion Services, Puget Sound Blood Center, Seattle, Washington.

Romiplostim stimulates the thrombopoeitin receptor, which is necessary for growth and maturation of bone marrow cells, and plays a very important role in increasing platelet counts, Dr. Gernsheimer explained at a press briefing on December 8.

In this study, 63 patients with chronic ITP who had undergone splenectomy were randomized to receive either placebo (n = 21) or romiplostim (n = 42) in a blinded fashion and were followed for 24 weeks to evaluate both efficacy and safety. Patients' ages ranged from 26 to 88 years, were extremely refractory to therapy, many required concurrent ITP therapy, and had a mean platelet count of about 15,000, which is well below a normal count of 150,000 to 400,000, Dr. Gernsheimer said.

The primary endpoint of the study was to determine durable platelet response, defined as the ability to maintain a platelet count above 50,000 for at least 6 of the last 8 weeks of the study.

The investigators also sought to determine whether treatment with romiplostim would enable patients to decrease or even discontinue their baseline medications. Six placebo and 12 romiplostim patients were on concurrent steroids or other immunosuppressant drugs when they entered the study.

Subcutaneous romiplostim or placebo was administered weekly for 24 weeks at a starting dose of 1 mcg/kg, and adjusted to maintain a target platelet count of 50,000 or above.

A durable response was achieved in 16 (38.1%) of the patients who were randomized to romiplostim compared with none of the placebo patients (P =.0013). An overall response -- defined as either a durable or transient platelet response for at least 4 weeks -- was seen in 33 (78.6%) of the romiplostim patients, but in none of the placebo patients.

"An overall response of approximately 80% is remarkable in a patient population like this, who were so refractory to therapy," Dr. Gernsheimer commented.

In addition, the mean number of weekly platelet responses was significantly greater in patients receiving romiplostim (12.3/24 weeks, 51%) compared with patients on placebo (12.3 vs 0.2 weeks, 51% vs 1%; P <.0001), Dr. Gernsheimer reported.

The study drug also reduced the proportion of patients who needed an increase in their baseline dose of concurrent medication or required new medication to increase their platelet counts. Eleven (26.2%) romiplostim-treated patients required rescue medications compared with 21 (57.1%) of placebo-treated patients (P =.0175). In addition, all of the patients who received romiplostim were able to either discontinue or reduce by more than 25% their use of concurrent ITP medications.

There were few serious adverse events related to romiplostim therapy. These included elevated bone marrow reticulin that returned to baseline 3 months after discontinuation of romiplostim in one patient, and thrombosis that was successfully treated in one patient. No patient developed neutralizing antibodies against either romiplostim or endogenous thrombopoeitin, Dr. Gernsheimer said.

Dr. Gernsheimer disclosed that she acts as a consultant and has a financial relationship with Amgen Inc., Thousand Oaks, California, which markets romiplostim.


[Presentation title: Evaluation of AMG 531 Efficacy in Splenectomized Patients With Chronic Immune Thrombocytopenic Purpura (ITP) in a Randomized Placebo-Controlled Phase 3 Study. Abstract 2]

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