Romiplostim induces rapid platelet response in adult patients with immune thrombocytopenia

Romiplostim (Nplate, Amgen), a synthetic protein that binds to and stimulates the thrombopoietin receptor, induced a rapid platelet response in most adult patients with immune thrombocytopenia (ITP) who had low platelet counts or bleeding symptoms, regardless of splenectomy status.

The drug also maintained a consistent safety profile, according to data from an international, phase 3, open-label, single-arm, prospective study presented December 13 at the 53rd Annual Meeting and Exposition of the American Society of Hematology (ASH), San Diego.

"These are the final results from the largest prospective study of the safety and efficacy of Nplate in adult patients with ITP to date," Susie Jun, MD, PhD, Amgen's global development lead for Nplate, told Formulary. "This data, along with findings reported from previous studies, confirm Nplate's ability to successfully treat these patients."

The primary study objective was incidence of adverse events and antibody formation. Secondary study objectives aimed at evaluating platelet responses defined as either (1) doubling of baseline count and a platelet count greater than or equal to 50,000 platelets/μL or (2) a platelet count increase greater than or equal to 20,000 platelets/μL from baseline. Results were reported by lead investigator, Ann Janssens of the Department of Hematology, University Hospitals Leuven, Belgium.

Patients enrolled in the study received romiplostim once weekly, with dose adjustments to maintain platelet counts of greater than or equal to 50,000 platelets/μL. Forty-one percent (168/407) of patients initiated romiplostim at a starting dose of 3 μg/kg/wk; 59% (239/407) initiated romiplostim at a starting dose of 1 μg/kg/wk. Median treatment duration was 44.29 weeks. Fifty-one percent of patients had previously undergone splenectomy.

Of the 71% of patients (288/407) who completed the study, 91% achieved a doubling of their platelet count to greater than or equal to 50,000 platelets/μLwith median time to response being 1 to 2 weeks depending on starting dose. The proportion of patients achieving a platelet response and median time to first response were comparable regardless of splenectomy status.

No adverse event occurred more than twice during the study. The most commonly reported were cerebrovascular accident, headache, bone marrow reticulin fibrosis, nausea, deep vein thrombosis, hemorrhage, and pulmonary embolism (2 [0.5%] patients each).

"Additional data presented at the meeting in other disease states help further elucidate the safety and efficacy profile of Nplate," said Sean E. Harper, MD, senior vice president of global development and chief medical officer at Amgen. "Collectively, these data help build upon our understanding of Nplate's treatment potential for patients with thrombocytopenia."

According to Dr Jun, Amgen will continue to monitor the safety profile of Nplate through clinical trials and post-marketing pharmacovigilance programs, as well as through other post-marketing commitments and follow-up ­measures.