- Romosozumab, a monoclonal antibody, is an injectable drug in development by Amgen which blocks the protein sclerostin. As a result of the drug's mode of action (MOA), it has been clinically proven in early-stage trials to build bone, while also preventing bone resorption.
- In a phase 3 trial, romosozumab decreased the risk of vertebral fracture by 73%, and the risk of all clinical fractures by 36%, compared with placebo.
- Amgen is facing competition in this space, notably from Radius Health, which is testing the rival abaloparatide for prevention of vertebral fractures and other types of fracture in high-risk post-menopausal women with osteoporosis.
Although analysts have some concerns about a potential competitive threat posed by Radius—their drug showed an 86% reduction in the risk of vertebral fracture—Amgen does have a major dosing-related advantage. Romosozumab is a once-monthly injectable while abaloparatide is a daily injectable.
In addition, romosozumab has shown superior efficacy in head-to-head trials with Lilly's Forteo—a $1.3 billion drug which is losing patent protection.
Then there's the matter of side effects. Lilly's Forteo carries a black box warning related to the risk of osteosarcoma, and analysts think that may also be the case with abaloparatide. By contrast, romosozumab will most likely not have a black box warning.
Assuming things go well, analysts are looking for romosozumab to become a blockbuster.