Which drug class includes alendronate, risedronate, and zoledronic acid?

• A. Calcitonin
• B. Bisphosphonates
• C. Selective estrogen receptor modulators
• D. Denosumab

Answer: (B)

These drugs are grouped as bisphosphonates, a class of antiresorptives that suppress osteoclast activity and bone resorption. They bind to bone mineral and are taken up by osteoclasts during resorption, where they inhibit the enzyme farnesyl pyrophosphate synthase in the mevalonate pathway. This disrupts prenylation of small GTPase proteins, impairing osteoclast function and promoting osteoclast apoptosis. The net effect is decreased bone turnover, higher bone mineral density, and a reduced risk of fractures in osteoporosis. Alendronate and risedronate are oral bisphosphonates (often weekly or monthly); zoledronic acid is given IV (often yearly). Other options involve different mechanisms: calcitonin is a peptide hormone that also reduces resorption but differently; selective estrogen receptor modulators act via estrogen receptors to protect bone; denosumab is a monoclonal antibody against RANKL, blocking osteoclast formation.