The updated results from the long-term study show that overall 87 percent of patients achieved a platelet response defined as a platelet count of 50,000 platelets per microliter or doubling of the baseline platelet count (124/142). The overall median baseline platelet count was 17,000 platelets per microliter. The average treatment period was 65 weeks, and the longest duration of treatment was 156 weeks. The results were presented today as an oral presentation at the 13th Congress of the European Hematology Association (Abstract # 1421).
"Currently, romiplostim is the only thrombopoietic treatment for adult chronic ITP for which there is three years of follow-up data," said Professor Adrian Newland, Department of Haematology, The Royal London Hospital, Whitechapel, London, UK. "This is the longest ITP study and the findings demonstrate the potential of romiplostim as a long-term treatment option for a patient population with limited treatment options."
Additional data presented include:
- Platelet response achieved: Overall, 87 percent (124/142) of patients achieved a platelet response. A platelet response was achieved by 30 percent (42/138) of patients after the first dose and by 51 percent (71/138) of patients after the third dose.
- Platelet counts increased: Platelet counts of romiplostim-treated patients were increased from baseline by 20,000 platelets per microliter more than half of the time in 86 percent of patients and more than four-fifths of the time in 57 percent of patients.
- Platelet counts maintained: Ad hoc analysis showed response durability, defined as platelet counts greater than 50,000 platelets per microliter, was maintained for greater than or equal to 10 consecutive weeks in 78 percent of patients (102/131), greater than or equal to 25 weeks in 54 percent of patients (66/122), and greater than or equal to 52 consecutive weeks in 35 percent of patients (29/84).
- Discontinuation or reduction of concurrent ITP medications: Of patients receiving concurrent ITP medications (such as corticosteroids) at baseline, 84 percent of patients (27/32) discontinued or reduced their dose by greater than 25 percent.
- Decreased use of rescue medications: Patients using rescue medications (defined as any additional ITP medicines needed to increase platelet counts) decreased from 23 percent (33/142) during weeks 1-12 to 15 percent during weeks 24-36, and remaining between 12-18 percent during weeks 130-132.
In this study, adverse events (AEs) did not increase in frequency during the course of the trial. AEs were reported in 95 percent of patients, with most mild to moderate in severity and transient in duration. The most common were headache (37 percent), nasopharyngitis (32 percent), contusion, fatigue and epistaxis (each 30 percent).
Treatment-related and serious AEs were reported in 36 percent and 31 percent of patients, respectively. Nine percent of serious AEs were considered treatment-related. Of the patients who discontinued treatment, seven percent (10/142) stopped due to AEs.
Bone marrow reticulin was reported in samples from eight patients with no evidence of collagen fibrosis or chronic idiopathic myelofibrosis. Thrombotic/thromboembolic events were reported in seven patients, of which six had pre-existing risk factors. To date, one patient developed a neutralizing antibody to romiplostim; however, it did not cross react with thrombopoietin and it was absent upon re-testing four months after romiplostim treatment was stopped.
About the Study
This ongoing, open-label study is assessing the safety and efficacy of long-term administration of romiplostim in both splenectomized and non-splenectomized adult chronic ITP patients. As of July 13, 2007, 143 patients had enrolled and 142 were treated with romiplostim. Sixty-seven percent of patients were female, and of the enrolled patients, 60 percent had undergone a splenectomy (removal of the spleen).
Eligible patients had completed a previous ITP romiplostim study, and had a baseline platelet count of less than 50,000 platelets per microliter, with no significant change in medical history. The romiplostim starting dose was 1 ug/kg by subcutaneous injection and was adjusted to maintain a platelet count between 50,000 and 250,000 platelets per microliter.
About Adult ITP
Platelets are blood cells needed to prevent bleeding. Low platelet counts leave adult ITP patients open to sudden serious bleeding events, making it impossible to arrest blood flow. The risk for serious bleeding events increases when platelet counts drop to less than 30,000 platelets per microliter.
There are limited approved treatments (i.e., corticosteroids, immunglobulins) or surgical therapy (removal of the spleen) available to adult patients with chronic ITP. Currently, there are 140,000 treated chronic ITP patients in the U.S. and Europe. ITP affects about twice as many adult women as men.
With ITP, platelets are destroyed by the patientâs own immune system. ITP has historically been considered a disease of platelet destruction. However, recent data also suggest that the bodyâs natural platelet production processes are unable to compensate for low levels of platelets in the blood. Increasing the rate of platelet production may address low platelet levels associated with ITP.
Romiplostim, Amgen's first peptibody, is a novel engineered therapeutic fusion protein with attributes of both peptides and antibodies, but is distinct from each. Romiplostim works similarly to thrombopoietin (TPO), a natural protein in the body. Romiplostim stimulates the TPO receptor, which is necessary for growth and maturation of bone marrow cells that produce platelets.
Amgen has filed for regulatory approval of romiplostim for use in the treatment of thrombocytopenia in adults with chronic ITP in the United States (U.S.), European Union, Australia and Canada. Regulatory authorities in the U.S., Australia and Canada have granted priority review of Amgenâs application.
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