Prolia is a so-called monoclonal antibody -- a fully human, lab-produced antibody that inactivates the body's bone-breakdown mechanism. It's the first "biologic therapy" to be approved for osteoporosis treatment.
Prolia is approved only for specific types of patients:
- Postmenopausal women with osteoporosis and high risk of fracture (that is, previous fracture due to osteoporosis or multiple fracture risk factors).
- Patients with osteoporosis for whom other osteoporosis treatments have failed.
- Patients who cannot tolerate other osteoporosis treatments.
The clinical trials on which Prolia approval is based lasted for three years. Over that time, postmenopausal women taking Prolia had fewer fractures and increased bone density.
Prolia targets a chemical signal called RANK ligand, an essential part of the body's natural process for breaking down bone.
Normally, the body constantly breaks down and rebuilds bone. Low estrogen levels in postmenopausal women unbalance this process in favor of bone breakdown.
That's where Prolia comes in. The drug slows the bone-breakdown process -- but also slows the entire bone-remodeling process. Over the long term, it's not yet clear what this will mean. Doctors are warned to be on the lookout for osteonecrosis of the jaw, atypical fractures, and delayed fracture healing in patients taking Prolia.
Another possible downside to Prolia is that its target, the RANK ligand, plays several roles in the immune system. In clinical trials, women taking Prolia had a higher risk of serious infections leading to hospitalization, including heart infections. Skin reactions such as dermatitis, rashes, and eczema also were reported.
The most common side effects seen in patients taking Prolia are back pain, pain in the extremities, muscle and bone pain, high cholesterol levels, and urinary bladder infections.
The drug also appears to lower calcium levels. Patients with low-bloodcalcium levels should not take Prolia until the condition is corrected.
Amgen, which makes Prolia, has established a "risk evaluation and mitigation strategy" to help patients understand the drug's risks. The company has also set up a surveillance program to monitor more than 4,500 women already taking the drug.
Compared to other biologic therapies, Prolia has a relatively moderate price. It's wholesale cost is $825 per injection or $1,650 per year. The drug will be available as early as next week.