Osteoporosis pharmacotherapy aims to reduce fracture risk by increasing bone mineral density and improving bone microarchitecture through inhibition of bone resorption or stimulation of bone formation. Osteoporosis is a systemic skeletal disease characterized by low bone mass and microarchitectural deterioration, leading to increased bone fragility and fracture susceptibility. It affects approximately 200 million women worldwide, with incidence increasing with age.
What Is Osteoporosis Pharmacotherapy?
Bone remodeling is a continuous process of resorption by osteoclasts and formation by osteoblasts. In osteoporosis, resorption exceeds formation, leading to net bone loss. Pharmacological interventions either suppress osteoclast-mediated bone resorption (antiresorptive agents) or stimulate osteoblast-mediated bone formation (anabolic agents). Treatment decisions are guided by bone mineral density T-scores, fracture history, and the FRAX fracture risk assessment tool.
Drug Classes and Mechanisms
Bisphosphonates are the most commonly prescribed antiresorptive agents. Alendronate (weekly oral), risedronate (weekly or monthly oral), ibandronate (monthly oral or quarterly intravenous), and zoledronic acid (annual intravenous) are pyrophosphate analogs that bind to hydroxyapatite in bone and are internalized by osteoclasts, inhibiting farnesyl pyrophosphate synthase and inducing osteoclast apoptosis. Denosumab is a monoclonal antibody against RANKL, preventing RANKL from activating RANK on osteoclast precursors, thereby inhibiting osteoclast formation, function, and survival. It is administered subcutaneously every 6 months. Teriparatide (recombinant PTH 1-34) and the full-length PTH analog are anabolic agents that stimulate osteoblast activity when administered intermittently, increasing bone formation and bone mass. Romosozumab is a monoclonal antibody against sclerostin, a negative regulator of bone formation, with a dual effect of increasing formation and decreasing resorption. SERMs such as raloxifene act as estrogen agonists in bone, reducing resorption with a modest effect on vertebral fracture risk. Calcitonin is a salmon-derived peptide that inhibits osteoclast activity but has been largely supplanted by more effective agents. Calcium and vitamin D supplementation is foundational to all osteoporosis therapy.
Therapeutic Uses
Bisphosphonates are first-line therapy for most patients with osteoporosis, with alendronate being the most commonly prescribed oral agent. Denosumab is an alternative for patients intolerant of or unresponsive to bisphosphonates. Teriparatide and romosozumab are reserved for patients at very high fracture risk or those who have failed or cannot tolerate other therapies. Treatment monitoring includes repeat bone mineral density testing every 1 to 2 years. A drug holiday may be considered after 3 to 5 years of bisphosphonate therapy in patients at low to moderate risk.
Adverse Effects
Bisphosphonates cause gastrointestinal intolerance with oral dosing, requiring strict adherence to administration instructions. They carry rare but serious risks of osteonecrosis of the jaw (particularly with high-dose intravenous use in cancer patients) and atypical femoral fractures with long-term use. Denosumab is well tolerated but causes hypocalcemia and requires timely dosing, as discontinuation leads to rapid bone turnover and increased fracture risk. Teriparatide causes transient hypercalcemia, nausea, and dizziness. Romosozumab carries a warning for cardiovascular events and must be avoided in patients with recent myocardial infarction or stroke. Raloxifene increases the risk of venous thromboembolism.
Key Clinical Considerations
Osteoporosis therapy should always be accompanied by adequate calcium (1000 to 1200 mg daily) and vitamin D (600 to 800 IU daily) intake. Dental evaluation is recommended before initiating high-dose bisphosphonate or denosumab therapy. After denosumab discontinuation, alternative therapy should be initiated to prevent rebound bone loss. Sequential therapy (anabolic followed by antiresorptive) may be beneficial in patients at very high fracture risk.
Conclusion
Bisphosphonates remain the mainstay of osteoporosis treatment, with denosumab providing an effective alternative. Anabolic agents such as teriparatide and romosozumab offer powerful options for high-risk patients. A comprehensive approach integrating pharmacotherapy with calcium, vitamin D, and lifestyle measures significantly reduces fracture incidence and improves outcomes in patients with osteoporosis.
