Teriparatide is indicated for severe osteoporosis or high fracture risk when antiresorptives are insufficient. What is its primary mechanism?

• A. Inhibits osteoclasts by mimicking estrogen.
• B. Severe osteoporosis or high fracture risk when antiresorptives are insufficient; stimulates osteoblast activity to build bone.
• C. Monoclonal antibody targeting RANKL.
• D. Vitamin D analog that increases calcium absorption.

Answer: (B)

Teriparatide works as an anabolic agent for bone. It is a parathyroid hormone analog given intermittently to stimulate osteoblast activity and bone formation, increasing bone mass and strength. This makes it particularly useful when osteoporosis is severe or fracture risk is high and antiresorptives (which slow bone resorption) aren’t enough. The goal is to tilt the remodeling balance toward formation rather than resorption. It is not a treatment that inhibits osteoclasts or blocks RANKL (that would be denosumab), nor a vitamin D analog that boosts calcium absorption.