Some may consider this a surprise, given that FDA reviewers expressed several concerns in their briefing documents about the Promacta treatment for chronic ITP prior to the advisory committee meeting. Those concerns included a failure to control bleeding any better than a placebo and Glaxo’s decision to seek approval for short-term use of a drug that may be used on a chronic basis.
Nonetheless, all 16 voting members of the panel decided that the clinical data supported its use short- term, defined as 6 weeks, which was the period studied. Nonetheless, some panel members did raise concners the drug may be used on a long-term basis. Chronic ITP, by the way, is an autoimmune disease that destroys blood platelets need for clotting and affects about 60,000 Americans.
Given the long-term term risks, which include liver toxicity, bleeding following drug discontinuation and potential marrow fibrosis, the panel agreed that a comprehensive management program is needed and that Glaxo and its partner, Ligand Pharmaceuticals, should bear at least part of the costs associated with developing a plan to restrict the use of the drug.
Richard Pazdur, who heads the FDA's Office of Oncologic Drugs, told Reuters he wasn't surprised by the panel's unanimous vote and noted the panel had debated many of the same issues about safety and effectiveness when it discussed Amgen competing drug, Nplate, which is also awaiting FDA approval. He added that labeling for Promacta would still need to be negotiated.
FDA approval of Promacta could help be a big boost for Glaxo, which sees Promacta as a potential blockbuster. Some analysts have forecast Promacta's annual sales could top $1 billion. While both drugs are designed to stimulate platelet production, Nplate is injected and is intended for long-term use, while Promacta is a pill and is intended for short-term use.
Thanks to Reuters