9.2 Antiresorptive Pharmacotherapy & Safety Considerations
Key Takeaways
Nitrogen-containing bisphosphonates inhibit FPPS. Denosumab binds RANKL, and raloxifene acts as a selective estrogen receptor modulator.
Ibandronate and raloxifene have vertebral fracture evidence. Hip fracture benefit is not established for either agent.
Use agent-specific administration and renal restrictions. Prolia has a boxed warning for severe hypocalcemia in advanced CKD.
New unexplained thigh or groin pain warrants evaluation for atypical femur fracture. Assess the contralateral femur when appropriate.
Match the agent to the fracture outcome and patient
Nitrogen-containing bisphosphonates bind bone mineral. During resorption, osteoclasts take up the drug. Inhibition of farnesyl pyrophosphate synthase in the mevalonate pathway reduces prenylation of proteins needed for osteoclast function. This includes small GTPases involved in cytoskeletal organization and vesicular trafficking. Denosumab binds RANKL and inhibits RANK-mediated formation, function and survival of osteoclasts. Raloxifene is a selective estrogen receptor modulator with estrogen agonist effects on bone. These agents differ in indications, duration of action, adverse effects and fracture outcomes.
| U.S. example regimen for postmenopausal osteoporosis | Fracture evidence to recognize |
|---|---|
| Alendronate 70 mg orally weekly | FIT showed lower vertebral and hip fracture risk with daily treatment in women with existing vertebral fractures. The weekly schedule is a labeled regimen. |
| Immediate-release risedronate 35 mg orally weekly or 150 mg monthly | Vertebral benefit was shown in VERT. The HIP trial found hip fracture reduction overall and in its group aged 70–79 selected for osteoporosis (1.9% with risedronate versus 3.2% with placebo). It did not show a significant hip benefit in the separate group aged 80 or older selected mainly by nonskeletal risk factors. |
| Ibandronate 150 mg orally monthly or 3 mg IV every three months | The BONE trial demonstrated vertebral fracture benefit with studied oral regimens. A hip or overall nonvertebral fracture benefit is not established. |
| Reclast 5 mg IV annually | HORIZON-PFT found fewer morphometric vertebral, hip and nonvertebral fractures over three years in women with postmenopausal osteoporosis. |
| Prolia 60 mg subcutaneously every six months | In the three-year placebo-controlled FREEDOM trial, denosumab reduced new radiographic vertebral, hip and nonvertebral fractures. |
| Raloxifene 60 mg orally daily | MORE demonstrated vertebral fracture benefit. A hip or overall nonvertebral fracture benefit is not established. U.S. labeling also includes reducing invasive breast cancer risk in specified postmenopausal women. |
Trial populations, durations, comparators and endpoints differ. For example, in HORIZON-PFT, new morphometric vertebral fracture occurred in 3.3% on zoledronic acid versus 10.9% on placebo. The absolute difference is 7.6 percentage points. The relative reduction is about 70%. That is a three-year vertebral outcome in a specified trial, and it does not give a patient's personal absolute benefit. In the separate HORIZON recurrent fracture trial after repair of low-trauma hip fracture, zoledronic acid reduced new clinical fractures. When hip protection is a priority, a convenient dosing interval does not establish that the agent has hip fracture evidence.
Apply product-specific precautions
For oral immediate-release alendronate and risedronate, use plain water and wait at least 30 minutes before the first food, drink other than water or other medicine. For oral ibandronate, wait at least 60 minutes. Follow the label for upright posture, the water amount and other instructions. Delayed-release risedronate has a different schedule. Esophageal conditions that delay emptying and inability to stay upright for the required time are important labeled restrictions for these oral products.
Renal assessment. Reclast is contraindicated when creatinine clearance is below 35 mL/min or with acute renal impairment. Use actual body weight in Cockcroft–Gault before each dose. Give the infusion over at least 15 minutes, and assess hydration and other renal risks. Fosamax is not recommended below 35 mL/min CrCl. Actonel and oral ibandronate are not recommended below 30 mL/min CrCl, and IV ibandronate should not be given below 30 mL/min CrCl. Fever and muscle aches can occur after zoledronic acid, particularly after the first dose.
Denosumab. Correct pre-existing hypocalcemia before Prolia. Its U.S. boxed warning applies to severe hypocalcemia in advanced CKD, particularly in CKD–mineral and bone disorder (CKD-MBD). At eGFR below 30 mL/min/1.73 m², including dialysis, evaluate for CKD-MBD using intact PTH, serum calcium, 25(OH)D and 1,25-dihydroxyvitamin D. Consider bone turnover assessment. If used, treatment requires CKD-MBD expertise, adequate calcium and activated vitamin D, and serum calcium monitoring weekly in the first month and monthly thereafter. No renal dose adjustment is specified. Plan doses and any transition before starting. Denosumab discontinuation can cause rapid bone loss and vertebral fractures, including multiple fractures. See monitoring and treatment changes for evidence on transition.
Raloxifene. Active or past venous thromboembolism is a U.S. contraindication. The boxed warning also describes an increased risk of death from stroke in women with coronary disease or at increased risk of coronary events. Review stroke risk and immobilization. The label directs interruption at least 72 hours before and during prolonged immobilization.
Recognize uncommon skeletal complications
Atypical femoral fracture (AFF). New unexplained thigh or groin pain during antiresorptive therapy warrants evaluation for incomplete fracture. The ASBMR case definition requires the specified femoral segment from just distal to the lesser trochanter to just proximal to the supracondylar flare and at least four of five major features. These cover minimal trauma, a fracture starting transversely at the lateral cortex, the extent of a complete or incomplete fracture, little or no comminution and focal lateral cortical thickening at the site. Assess the contralateral femur when AFF is suspected or identified. ISCD full-length DXA imaging can identify and report suspicious findings. A symptomatic patient may need diagnostic radiographs and further imaging if suspicion persists. Management depends on the findings and the current drug.
Medication-related osteonecrosis of the jaw (MRONJ). The AAOMS case definition includes current or previous antiresorptive use alone or with immune modulators or antiangiogenic medications, exposed maxillofacial bone or bone probeable through a fistula for longer than eight weeks, and no jaw irradiation or metastases to the jaws. Risk is generally lower in osteoporosis-dose treatment than in oncology-dose treatment. Discuss oral health and coordinate necessary dental care. A universal dental drug holiday is unsupported, and changing denosumab requires a plan to address vertebral fracture risk.
Fosamax · Actonel · Oral ibandronate · IV ibandronate · Reclast · Prolia · Evista
FIT · VERT · HIP · BONE · HORIZON-PFT · HORIZON-RFT · FREEDOM · MORE · ASBMR AFF criteria · ISCD full-length femur position · AAOMS position
A 72-year-old woman with osteoporosis and high hip fracture risk requests a monthly oral agent. Which point should guide discussion of ibandronate?
The monthly schedule establishes hip fracture protection equivalent to alendronate.
Ibandronate is preferred because hip fracture benefit is larger than its vertebral benefit.
The monthly regimen rules out the need to review renal function.
Ibandronate has vertebral fracture evidence. If hip fracture reduction is a priority, discuss options with demonstrated hip fracture benefit.
A patient on Prolia every six months is considering stopping after several years because BMD has improved. What should the clinician explain?
Stopping can cause rapid bone loss and vertebral fractures. Arrange a follow-on antiresorptive plan if treatment will stop.
Improved BMD permits a two-year holiday with no need to discuss other therapy.
The drug remains bound to bone mineral and continues protecting against fracture for years.
A fixed dose of calcium can replace antiresorptive therapy after discontinuation.
A 74-year-old woman who has taken alendronate for seven years reports new persistent thigh and groin pain without trauma. What is the appropriate next step?
Diagnose AFF on symptoms alone and start teriparatide.
Evaluate promptly for an incomplete AFF with diagnostic femur imaging and assess the contralateral femur as appropriate.
Wait for a scheduled standard hip DXA because pain without trauma excludes fracture.
Diagnose osteonecrosis of the jaw from the duration of exposure.
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