NCLEX Review Guide: Osteoporosis Medications

Mechanism of Action

• Bisphosphonates inhibit osteoclast-mediated bone resorption by binding to hydroxyapatite binding sites on bone surfaces, especially those undergoing active resorption. When osteoclasts begin to resorb bone that contains bisphosphonate, the drug is released and impairs the osteoclasts' ability to form the ruffled border and their proton pump, causing loss of resorptive function.
• These medications effectively reduce bone turnover, increase bone mineral density, and reduce fracture risk in both postmenopausal women and men with osteoporosis.

Common Bisphosphonates

• Alendronate (Fosamax): Oral bisphosphonate typically dosed weekly (70mg) for osteoporosis treatment or daily (10mg) for prevention. First-line therapy for many patients with osteoporosis.
• Risedronate (Actonel): Oral bisphosphonate available in daily, weekly, or monthly dosing schedules. Demonstrates rapid onset of fracture reduction compared to some other bisphosphonates.
• Ibandronate (Boniva): Available as monthly oral tablet (150mg) or quarterly IV injection (3mg). Less commonly used than alendronate or risedronate.
• Zoledronic acid (Reclast): Administered as annual IV infusion (5mg), making it useful for patients with adherence issues or contraindications to oral therapy.

Adverse Effects

• Esophageal Irritation/Ulceration: Oral bisphosphonates can cause significant esophageal irritation if not taken correctly. Proper administration instructions are critical to prevent this potentially serious adverse effect.
• Osteonecrosis of the Jaw (ONJ): Rare but serious condition involving exposed bone in the maxillofacial region that fails to heal within 8 weeks. Risk is higher with IV formulations, longer duration of therapy, and in patients undergoing invasive dental procedures.
• Atypical Femur Fractures: Rare subtrochanteric or diaphyseal femur fractures associated with long-term bisphosphonate use. Patients often report prodromal thigh pain weeks to months before fracture occurs.
• Acute phase reactions (flu-like symptoms) are common with IV bisphosphonates, particularly after first infusion, and typically resolve within 24-72 hours.

Denosumab (Prolia, Xgeva)

• Denosumab is a fully human monoclonal antibody that binds to RANKL (Receptor Activator of Nuclear Factor kappa-B Ligand), preventing its interaction with RANK receptors on osteoclast precursors. This inhibits osteoclast formation, function, and survival, thereby decreasing bone resorption.
• Unlike bisphosphonates, denosumab is not incorporated into bone and has a reversible effect that diminishes within 6 months of discontinuation. It is administered as a subcutaneous injection every 6 months (60mg for osteoporosis).

Adverse Effects and Considerations

• Hypocalcemia: Denosumab can cause significant hypocalcemia, especially in patients with renal impairment. Calcium and vitamin D supplementation is required before and during therapy.
• Rebound Bone Loss: Abrupt discontinuation of denosumab can lead to rapid bone loss and increased risk of vertebral fractures. Transition to another osteoporosis therapy should be considered if discontinuing.
• Other adverse effects include increased risk of infections (particularly cellulitis), dermatological reactions, ONJ (similar risk as with bisphosphonates), and atypical femur fractures.

Teriparatide and Abaloparatide

• Teriparatide (Forteo) is a recombinant form of parathyroid hormone (PTH 1-34) that stimulates new bone formation when administered intermittently. It works primarily by increasing osteoblast activity and number, leading to increased bone formation that exceeds bone resorption.
• Abaloparatide (Tymlos) is a synthetic analog of parathyroid hormone-related protein (PTHrP) that selectively activates the PTH type 1 receptor, favoring the pathway that stimulates bone formation over bone resorption.

Romosozumab (Evenity)

• Romosozumab is a monoclonal antibody that binds to and inhibits sclerostin, a protein produced by osteocytes that normally inhibits bone formation. By blocking sclerostin, romosozumab increases bone formation while simultaneously decreasing bone resorption.
• Administered as two consecutive subcutaneous injections once monthly for 12 months, after which patients should transition to an antiresorptive therapy to maintain bone density gains.

Raloxifene (Evista)

• Raloxifene selectively binds to estrogen receptors, acting as an agonist in bone and lipid metabolism but as an antagonist in breast and uterine tissue. In bone, it mimics the beneficial effects of estrogen by decreasing bone resorption.
• Primarily effective at reducing vertebral fracture risk (30-50% reduction) but has not demonstrated significant reduction in non-vertebral or hip fractures. It also reduces the risk of invasive breast cancer in postmenopausal women.

Bisphosphonates vs. Denosumab

Anabolic Agents vs. Antiresorptive Agents

Oral Bisphosphonate Administration

1. Take first thing in the morning on an empty stomach
2. Take with a full glass (6-8 oz) of plain water only (no mineral water, coffee, juice, etc.)
3. Remain upright (sitting or standing) for at least 30-60 minutes after taking
4. Wait at least 30-60 minutes before eating, drinking anything other than water, or taking other medications
5. Do not lie down until after first food of the day

Monitoring Therapy

• Bone mineral density (BMD) testing is typically performed every 1-2 years initially, then less frequently if stable.
• Biochemical markers of bone turnover (e.g., CTX, P1NP) may be used to assess response to therapy, especially with anabolic agents.
• For patients on bisphosphonates, consider a drug holiday after 3-5 years (risedronate, alendronate) or 3 years (zoledronic acid) for moderate-risk patients, or after 10 years for high-risk patients.
• For denosumab, never implement a drug holiday without transitioning to another therapy due to rebound bone loss.

Common Pitfalls

Self-Assessment

Check your understanding:

I understand the mechanisms of action for different osteoporosis medications
I can explain the proper administration of oral bisphosphonates
I understand the differences between anabolic and antiresorptive agents
I know the major adverse effects to monitor for each class of medication
I understand when drug holidays are appropriate and when they are not