Bone safety of long-term bisphosphonate treatment

Anti-resorptive therapy in the osteometabolic patient affected by periodontitis. A joint position paper of the Italian Society of Orthopaedics and Traumatology (SIOT) and the Italian Society of Periodontology and Implantology (SIdP)

This joint report from the Italian Society of Orthopaedics and Traumatology (SIOT) and the Italian Society of Periodontology and Implantology (SIdP) aims for a consensus around the scientific rationale and clinical strategy for the management of osteoporotic patients affected by periodontitis who are undergoing anti-resorptive (AR) therapy to manage the risk of the occurrence of a medication-related osteonecrosis of the jaws (MRONJ). Osteoporosis and periodontitis are chronic diseases with a high prevalence in aging patients, and they share some of the same pathogenetic mechanisms based upon inflammation. Available evidence shows the relationship among osteoporosis, AR agents, periodontitis and implant therapy in relation to the incidence of MRONJ. Uncontrolled periodontitis may lead to tooth loss and to the need to replace teeth with dental implants. Tooth extraction and surgical dental procedures are recognized as the main risk factors for developing MRONJ in individuals taking AR therapy for osteometabolic conditions. Although the incidence of MRONJ in osteometabolic patients taking AR therapy may be as low as 0.9%, the increasing prevalence of osteoporosis and the high prevalence of periodontitis suggest that this potential complication should not be overlooked. Good clinical practice (GCP) guidelines are proposed that aim at a more integrated approach (prescriber, dentist, periodontist and dental hygienist) in the management of periodontitis patients undergoing AR therapy for osteometabolic disorders to reduce the risk of MRONJ. Dental professional and prescribers should educate patients regarding the potential risk associated with the long-term use of AR therapy and oral health behavior.

The osteoporosis treatment gap in Switzerland between 1998 and 2018

The annual number of patients treated for osteoporosis between 1998 and 2018 in Switzerland increased until 2008 and steadily decreased thereafter. With a continuously growing population at fracture risk exceeding an intervention threshold, the treatment gap has increased and the incidence of hip fractures has stopped declining in the past decade.

INTRODUCTION

The existence of an osteoporosis treatment gap, defined as the percentage of patients at risk for osteoporotic fractures exceeding an intervention threshold but remaining untreated, is widely acknowledged. Between 1998 and 2018, new bone active substances (BAS) indicated for the treatment of osteoporosis became available. Whether and if so to what extent these new introductions have altered the treatment gap is unknown.

METHODS

The annual number of patients treated with a BAS was calculated starting from single-drug unit sales. The number of patients theoretically eligible for treatment with a BAS was estimated based on four scenarios corresponding to different intervention thresholds (one based solely on a bone mineral density T score threshold and three FRAX-based thresholds) and the resulting annual treatment gaps were calculated.

RESULTS

In Switzerland, the estimated number of patients on treatment with a BAS increased from 35,901 in year 1998 to 233,381 in year 2018. However, this number grew regularly since 1998, peaked in 2008, and steadily decreased thereafter, in timely coincidence with the launch of intravenous bisphosphonates and the RANKL inhibitor denosumab. When expressed in numbers of untreated persons at risk for osteoporotic fractures exceeding a given intervention threshold, the treatment gaps were of similar magnitude in 1998 (when the first BSAs just had become available) and 2018. There was a strong association, which does not imply causation, between the proportion of patients treated and hip fracture incidence.

CONCLUSION

In Switzerland, the osteoporosis treatment gap has increased over the past decade. The availability of new BAS has not contributed to its decrease.

Vascular response to stress: Protective action of the bisphosphonate alendronate

BACKGROUND

Since several additional actions of bone bisphosphonates have been proposed, we studied the effect of the bisphosphonate alendronate (ALN) on the vascular response to environmental stress.

METHODS

Primary cultures of endothelial cells (EC) and vascular smooth muscle cells (VSMC) exposed to strained conditions were employed for experimental evaluation. After ALN treatment, cell migration, proliferation, and angiogenesis assays were performed. The participation of signal transduction pathways in the biochemical action of ALN was also assessed.

RESULTS

In VSMC cultures, ALN counteracted the stimulation of cellular migration elicited by the proinflammatory agent lipopolysaccharide (LPS) or by high levels of calcium and phosphorus (osteogenic medium). Indeed, ALN reduced the increase of VSMC proliferation evoked by the stressors. When LPS and osteogenic medium were added simultaneously, the enhancement of cell proliferation dropped to control values in the presence of ALN. The mechanism of action of ALN involved the participation of nitric oxide synthase, mitogen-activated protein kinase (MAPK), and protein kinase C (PKC) signaling pathways. The study revealed that ALN exhibits a proangiogenic action. On EC, ALN enhanced vascular endothelial growth factor (VEGF) synthesis, and induced capillary-like tube formation in a VEGF-dependent manner. The presence of vascular stress conditions (LPS or osteogenic medium) did not modify the proangiogenic action elicited by ALN.

CONCLUSION

The findings presented suggest an extra-bone biological action of ALN, which could contribute to the maintenance of vascular homeostasis avoiding cellular damage elicited by environmental stress.

Aminobisphosphonates: Reconsideration 25 years after their approval for the treatment of osteoporosis

Aminobisphosphonates are widely used in the treatment of osteoporosis. They have a high affinity for hydroxyapatite, binding primarily to resorbing surfaces, but also to forming surfaces and to some extent to resting surfaces. They inhibit osteoclasts, thereby decreasing remodelling units. Consequently, they increase bone mass and reduce stress risers. This decreases the risk of fractures. If this decrease is sufficient, they can be temporarily withdrawn (drug holidays), which prevents serious complications (atypical femoral fracture). They probably reduce mortality. Virtually all patients with osteoporosis can benefit from them at some point in the course of their disease (at the beginning of treatment or after the administration of anabolics, selective estrogen receptor modulators or denosumab). If well tolerated orally, alendronate and risedronate are preferable. Otherwise, zoledronate is preferred. Their efficacy vs. cost-safety-convenience ratio makes aminobisphosphonates reference drugs in the field of osteoporosis.

Bone Quality and Fractures in Women With Osteoporosis Treated With Bisphosphonates for 1 to 14 Years

Oral bisphosphonates are the primary medication for osteoporosis, but concerns exist regarding potential bone-quality changes or low-energy fractures. This cross-sectional study used artificial intelligence methods to analyze relationships among bisphosphonate treatment duration, a wide variety of bone-quality parameters, and low-energy fractures. Fourier transform infrared spectroscopy and histomorphometry quantified bone-quality parameters in 67 osteoporotic women treated with oral bisphosphonates for 1 to 14 years. Artificial intelligence methods established two models relating bisphosphonate treatment duration to bone-quality changes and to low-energy clinical fractures. The model relating bisphosphonate treatment duration to bone quality demonstrated optimal performance when treatment durations of 1 to 8 years were separated from treatment durations of 9 to 14 years. This may be due to a change in relationship of bone-quality parameters with treatment duration. This model also showed that the effects of bisphosphonate treatment duration were most highly correlated with changes in means and standard deviations of infrared spectroscopically derived mineral and matrix parameters and histomorphometric bone turnover parameters. A second model related treatment duration to bone fracture in all 22 patients who fractured while on treatment with bisphosphonates for more than 8 years. This second model showed that bisphosphonate treatment duration, not hip bone mineral density (BMD), was the most strongly correlated parameter to these low-energy bone fractures. Application of artificial intelligence enabled analysis of large quantities of structural, cellular, mineral, and matrix bone-quality parameters to determine relationships with long-term oral bisphosphonate treatment and fracture. Infrared spectroscopy provides clinically relevant bone-quality information of which bone mineral purity is among the most relevant. Nine or more years of bisphosphonate treatment was associated with abnormal bone mineral purity, matrix abnormalities, and low-energy fractures. These data justify limiting bisphosphonate treatment duration to 8 years. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Duration of Bisphosphonate Drug Holidays in Osteoporosis Patients: A Narrative Review of the Evidence and Considerations for Decision-Making

Bisphosphonates are first-line therapy for osteoporosis, with alendronate, risedronate, and zoledronate as the main treatments used globally. After one year of therapy, bisphosphonates are retained in bone for extended periods with extended anti-fracture effects after discontinuation. Due to this continued fracture protection and the potential for rare adverse events associated with long-term use (atypical femoral fractures and osteonecrosis of the jaw), a drug holiday of two to three years is recommended for most patients after long-term bisphosphonate therapy. The recommendation for a drug holiday up to three years is derived primarily from extensions of pivotal trials with alendronate and zoledronate and select surrogate marker studies. However, certain factors may modify the duration of bisphosphonate effects on a drug holiday and warrant consideration when determining an appropriate time off-therapy. In this narrative review, we recall what is currently known about drug holidays and discuss what we believe to be the primary considerations and areas for future research regarding drug holiday duration: total bisphosphonate exposure, type of bisphosphonate used, bone mineral density and falls risk, and patient sex and body weight.

The effects of teriparatide and bisphosphonates on new fractures in postmenopausal women with osteoporosis: A protocol for systematic review and meta-analysis

BACKGROUND

To systematically evaluate the efficacy of teriparatide and bisphosphonates in preventing fractures in postmenopausal women with osteoporosis.

MATERIALS AND METHODS

We performed a systematic search of PubMed, Embase, and the Cochrane Library for randomized controlled trials (RCTs) that compared teriparatide and bisphosphonates for osteoporosis treatment. Searches were performed without language restrictions and included studies from beginning of time to March 2019. Two authors independently screened and extracted the selected article. The quality of the included studies was evaluated using the Cochrane system evaluation method. Data were extracted and analysed using RevMan 5.2 software.

RESULTS

Nine RCTs were included for a total of 2990 postmenopausal women with osteoporosis. Of these, 1515 patients were treated with teriparatide and 1475 were treated with bisphosphonates. After pooling the data of 9 studies, there were significant differences between teriparatide and bisphosphonates [relative risk (RR): 0.61, 95% confidence interval (CI) (0.51, 0.74)] in the prevention of fractures according to different follow-up durations (P < .05), whatever alendronate [RR: 0.51, 95% CI (0.27, 0.95)] and other bisphosphonates [RR: 0.63, 95% CI (0.51, 0.77)]. In addition, we found significant differences between teriparatide and bisphosphonates in the prevention of vertebral fractures [RR: 0.47, 95% CI (0.35, 0.64)] and non-vertebral fractures [RR: 0.76, 95% CI (0.58,0.99)]. There were no significant differences in adverse effects between teriparatide and bisphosphonates [RR: 0.89, 95% CI (0.76, 1.03)].

CONCLUSIONS

Based on the results of our meta-analysis, teriparatide was better than bisphosphonates in preventing fractures in postmenopausal women with osteoporosis both in the short-term and long-term follow-up periods. Teriparatide was superior to bisphosphonates in preventing vertebral and non-vertebral fractures. These drugs did not differ in terms of their adverse effects. More high-quality studies are needed to compare other factors such as costs and adverse reactions.

Evaluation and management of atypical femoral fractures: an update of current knowledge

Atypical femoral fractures are often attributed to the use of anti-resorptive medications such as bisphosphonates (BP). Whilst they have proven effects on fragility fracture prevention, clinical and laboratory evidence is evolving linking BP-related suppression of bone remodelling to the development of atypical stress-related sub-trochanteric fractures (Shane et al. in JBMR 29:1-23, 2014; Odvina et al. in JCEM 90:1294-301, 2005; Durchschlag et al. in JBMR 21(10):1581-1590, 2006; Donnelly et al. in JBMR 27:672-678, 2012; Mashiba et al. in Bone 28(5):524-531, 2001; Dell et al. in JBMR 27(12):2544-2550, 2012; Black et al. in Lancet 348:1535-1541, 1996; Black et al. in NEJM 356:1809-1822, 2007; Black et al. in JAMA 296:2927-2938, 2006; Schwartz et al. in JBMR 25:976-82, 2010). Injuries may present asymptomatically or with prodromal thigh pain and most can be successfully managed with cephalomedullary nailing and discontinuation of BP therapy. Such injuries exhibit a prolonged time to fracture union with high rates of non-union and metal-work failure when compared to typical subtrochanteric osteoporotic femoral fractures. Despite emerging literature on AFFs, their management continues to pose a challenge to the orthopaedic and extended multi-disciplinary team. The purpose of this review includes evaluation of the current evidence supporting the management of AFFs, clinical and radiological features associated with their presentation and a review of reported surgical strategies to treat and prevent these devastating injures.

Bisphosphonates and parathyroid hormone analogs for improving bone quality in spinal fusion: State of evidence

Spinal fusion is among the most commonly performed surgical procedures for elderly patients with spinal disorders - including degenerative disc disease with spondylolisthesis, deformities, and trauma. With the large increase in the aging population and the prevalence of osteoporosis, the number of elderly osteoporotic patients needing spinal fusion has risen dramatically. Due to reduced bone quality, postoperative complications such as implant failures, fractures, post-junctional kyphosis, and pseudarthrosis are more commonly seen after spinal fusion in osteoporotic patients. Therefore, pharmacologic treatment strategies to improve bone quality are commonly pursued in osteoporotic cases before conducting spinal fusions. The two most commonly used pharmacotherapeutics are bisphosphonates and parathyroid hormone (PTH) analogs. Evidence indicates that using bisphosphonates and PTH analogs, alone or in combination, in osteoporotic patients undergoing spinal fusion, decreases complication rates and improves clinical outcomes. Further studies are needed to develop guidelines for the administration of bisphosphonates and PTH analogs in osteoporotic spinal fusion patients in terms of treatment duration, potential benefits of sequential use, and the selection of either therapeutic agents based on patient characteristics.

Temporal Trends and Factors Associated with Bisphosphonate Discontinuation and Restart

Adverse events related to long-term use of bisphosphonates have raised interest in temporary drug discontinuation. Trends in bisphosphonate discontinuation and restart, as well factors associated with these decisions, are not fully understood at a population level. We investigated temporal trends of bisphosphonate discontinuation from 2010 to 2015 and identified factors associated with discontinuation and restart of osteoporosis therapy. Our cohort consisted of long-term bisphosphonate users identified from 2010 to 2015 Medicare data. We defined discontinuation as ≥12 months without bisphosphonate prescription claims. We used conditional logistic regression to compare factors associated with alendronate discontinuation or osteoporosis therapy restart in the 120-day period preceding discontinuation or restart referent to the 120-day preceding control periods. Among 73,800 long-term bisphosphonate users, 59,251 (80.3%) used alendronate, 6806 (9.2%) risedronate, and 7743 (10.5%) zoledronic acid, exclusively. Overall, 26,281 (35.6%) discontinued bisphosphonates for at least 12 months. Discontinuation of bisphosphonates increased from 1.7% in 2010, reaching a peak of 14% in 2012 with levels plateauing through 2015. The factors most strongly associated with discontinuation of alendronate were: benzodiazepine prescription (adjusted odds ratio [aOR] = 2.5; 95% confidence interval [CI] 2.1, 3.0), having a dual-energy X-ray absorptiometry (DXA) scan (aOR = 1.8; 95% CI 1.7, 2.0), and skilled nursing facility care utilization (aOR = 1.8; 95% CI 1.6, 2.1). The factors most strongly associated with restart of osteoporosis therapy were: having a DXA scan (aOR = 9.9; 95% CI 7.7, 12.6), sustaining a fragility fracture (aOR = 2.8; 95% CI 1.8, 4.5), and an osteoporosis or osteopenia diagnosis (aOR = 2.5; 95% CI 2.0, 3.1). Our national evaluation of bisphosphonate discontinuation showed that an increasing proportion of patients on long-term bisphosphonate therapy discontinue medications. The factors associated with discontinuation of alendronate were primarily related to worsening of overall health status, whereas traditional factors associated with worsening bone health were associated with restarting osteoporosis medication. © 2019 American Society for Bone and Mineral Research.

Bisphosphonate drug holidays: One size does not fit all

Bisphosphonates have been safely used to treat osteoporosis, effectively reducing fracture risk after 3 to 5 years of treatment. Recent concerns about long-term safety coupled with posttreatment fracture risk reduction have increased support for drug holidays. The decision to start low-risk patients on drug holidays must be based on current fracture risk assessment.

Efficacy and safety of denosumab vs. bisphosphonates in postmenopausal women previously treated with oral bisphosphonates

Transitioning postmenopausal women with osteoporosis from a bisphosphonate to denosumab appears to be safe and more effective at improving BMD than continuing treatment with a bisphosphonate.

INTRODUCTION

We conducted a patient-level pooled analysis of four studies to estimate the efficacy and safety of transitioning to denosumab vs. continuing bisphosphonate treatment in postmenopausal women who previously received oral bisphosphonates.

METHODS

Patients received 60 mg denosumab once every 6 months or a bisphosphonate (oral alendronate, risedronate, ibandronate, or intravenous zoledronic acid). Endpoints were change from baseline in lumbar spine, total hip, femoral neck, and 1/3 radius BMD at month 12, change from baseline in serum CTX-1 and P1NP, and incidence of adverse events.

RESULTS

A total of 2850 randomized patients (1424 bisphosphonate:1426 denosumab) were included in the analysis. Percentage change in BMD was significantly greater (p < 0.001) for denosumab vs. bisphosphonate at each skeletal site; differences in BMD changes ranged from 0.6 to 2.0%. Percentage decrease in serum CTX-1 and P1NP was significantly greater (p < 0.0001) for denosumab vs. bisphosphonate at months 1, 6, and 12; in the denosumab group only, percentage change in serum CTX-1 at month 1 was significantly correlated with percentage change in lumbar spine and total hip BMD at month 12. The incidences of adverse events were similar between treatment groups. Three patients (one bisphosphonate and two denosumab) had atypical femoral fractures, all from the denosumab vs. zoledronic acid study.

CONCLUSION

Postmenopausal women can safely transition from a bisphosphonate to denosumab, which is more effective at improving BMD than continuing with a bisphosphonate.

CLINICAL TRIALS REGISTRATION

NCT00377819, NCT00919711, NCT00936897, NCT01732770.

Effectiveness of thiazides on serum and urinary calcium levels and bone mineral density in patients with osteoporosis: a systematic review and meta-analysis

Objective

Osteoporosis is the most common metabolic bone disease and a major public health problem worldwide. Thiazides are widely used as antihypertensive agents with good tolerability and efficacy. Furthermore, thiazides have long been regarded as candidates for the prevention of postmenopausal bone loss. However, there is insufficient evidence that thiazides have a sustained beneficial effect on preserving bone mass and preventing osteoporosis to date.

Materials and methods

We searched the PubMed, the Cochrane Library, and Embase in June 2018 for randomized controlled trials on the use of thiazides to treat osteoporosis. Continuous outcomes are presented as the standardized mean difference (SMD) and 95% CI. Furthermore, P-values <0.05 were considered significant.

Results

Five trials with 756 patients were randomly assigned in the five trials included in this meta-analysis. Serum calcium level was higher in the thiazide group than in the control group (SMD 0.33, 95% CI [0.16, 0.50]), and urinary calcium level was significantly lower in the thiazide group (SMD −0.35, 95% CI [−0.52, −0.17]). There was no significant difference in bone mineral density between the two groups (SMD 0.19, 95% CI [−0.16, 0.54]).

Conclusion

Thiazides might play a role in preserving bone mass and be effective in the prevention and treatment of osteoporosis. Future high-quality trials are needed to confirm our findings in the future.

A Review of Osteoporosis in the Older Adult: An Update

Osteoporosis in the elderly population is common. It results in more than 1.5 million fractures per year in the United States. The goal of managing osteoporosis is to prevent fractures. In men, osteoporosis is underrecognized and undertreated. More men than women die every year as a consequence of hip fractures. Bisphosphonates are the first-line treatment of men and women. In the past several years, advances in bone biology have resulted in major therapeutic advances. A review of diagnosis and treatment of osteoporosis is described.

A Review of Osteoporosis in the Older Adult

Osteoporosis in the elderly population is common. It results in more than 1.5 million fractures per year in the United States. The goal of managing osteoporosis is to prevent fractures. In men, osteoporosis is underrecognized and undertreated. More men than women die every year as a consequence of hip fractures. A review of diagnosis and treatment of osteoporosis is described in this article. Bisphosphonates are the first-line treatment for men and women. In the past several years, advances in bone biology have resulted in major therapeutic advances.

Denosumab: targeting the RANKL pathway to treat rheumatoid arthritis

INTRODUCTION

Rheumatoid arthritis (RA) is a chronic inflammatory disorder characterized by focal pathologic bone resorption due to excessive activity of osteoclasts (OC). Receptor activator of nuclear factor kappa B ligand (RANKL) is essential for the proliferation, differentiation, and survival of OC. Denosumab (DMab) is a humanized monoclonal antibody that binds to RANKL with high affinity and blocks its subsequent association with its receptor RANK on the surface of OC precursors. Area covered: The authors review the molecular and cellular mechanisms underlying therapeutic applications of DMab, provide recent highlights on pharmacology, efficacy and safety of DMab, and discuss the potential of DMab as a novel therapeutic option for the treatment of rheumatoid arthritis. Expert opinion: Clinical results suggest that DMab is efficient both in systemic and articular bone loss in RA with limited side effects. Diminished bone erosion activity was also noted in RA patients on corticosteroids and bisphosphonates. Combination of DMab with an anti-TNF agent was not associated with increased infection rates. Collectively, these data indicate that DMab, in combination with methotrexate and possibly other conventional synthetic Disease Modifying Anti-Rheumatic Drugs (csDMARDs), is an effective, safe and cost-effective option for the treatment of RA.

Long-Term Use of Bisphosphonates in Osteoporosis

The rate of bone turnover increases around the time of menopause, and new bone may be remodeled before it is has been completely mineralized. If this is left untreated, osteoporosis often develops, leading to fractures, particularly of the spine and hip, which represent an enormous burden in terms of suffering, healthcare expenditure, disabilities and death. Bisphosphonates are potent inhibitors of bone resorption, which slow or arrest progressive bone loss. Continuous treatment with bisphosphonates reduces bone turnover, improves bone microarchitecture and increases bone mass, leading to greater mechanical strength and reduced fracture risk. Since osteoporosis is a chronic, progressive condition, treatment has to continue for many years. Therefore, the efficacy and safety of bisphosphonates, particularly alendronate and risedronate, have been evaluated in many thousands of patients for up to 10 years of continuous use. These drugs remain the cornerstone of osteoporosis treatment and appear to have favorable safety and efficacy profiles throughout long-term usage.

Clinical and radiographic evaluation of effect of risedronate 5 mg as an adjunct to treatment of chronic periodontitis in postmenopausal women (12-month study)

Bisphosphonates are beneficial to women, after menopause, in treatment of gum diseases. In this study, significant improvement in the disease condition was found and that no further progress was noted, and no side effects were reported. Bisphosphonates can be safely and successfully be used to support oral health procedures.

INTRODUCTION

The purpose of this study was to evaluate host modulating effect of bisphosphonate adjunct with the treatment of chronic periodontitis in osteopenic and osteoporotic postmenopausal women.

METHODS

Twenty-two osteopenic and osteoporotic postmenopausal women with moderate to severe chronic periodontitis were selected for the study. On intraoral examination, periodontal parameters like probing depth (PD), clinical attachment level (CAL), Plaque Index (PI) and Gingival Index (GI) were recorded. Scaling and root planing were done. Intraoral periapical X-rays were taken, and alveolar bone density (ABD) was measured with cone beam computed tomography (CBCT), and then, medications (risedronate 5 mg once daily (OD), calcium citrate 250 mg OD, vitamin D 400 IU OD) were given. Patients were recalled for follow-up at 3, 6 and 12 months. Intraoral periapical (IOPA) X-rays were taken at 6 and 12 months and ABD was measured at baseline and 12 months.

RESULTS

There was a significant improvement in all the parameters. There was an increase of 0.02 ± 0.001 cm on CT scan and 0.38 ± 0.005 mm on IOPA in bone height over 12 months from baseline. Bone density increased by 118.56 ± 3.251 Hounsfield units (HU). There was no progress in the disease, and further bone loss was not noticed. This is in correlation with clinical parameters which showed highly significant gain in CAL (3.57 ± 0.234 mm) and reduction in PD (2.20 ± 0.229 mm)

CONCLUSIONS

Bisphosphonate therapy as an adjunct to scaling and root planing may have significant beneficial clinical effects on the periodontium of postmenopausal women with moderate to severe chronic periodontitis.

Position Statement: Drug Holiday in Osteoporosis Treatment with Bisphosphonates in South Korea

Bisphosphonates have been widely used in the treatment of osteoporosis with robust data from many placebo-controlled trials demonstrating its efficacy in fracture risk reduction over 3 to 5 years of treatment. Although bisphosphonates are generally safe and well tolerated, concerns have emerged about the adverse effects related to its long-term use, including osteonecrosis of the jaw and atypical femur fractures. Because bisphosphonates are incorporated into the skeleton and continue to exert an anti-resorptive effect for a period of time after the discontinuation of drugs, the concept of a "drug holiday" has emerged, whereby the risk of adverse effects might be decreased while the patient still benefits from anti-fracture efficacy. As randomized clinical trial evidence is not yet available on who may qualify for a drug holiday, there is considerable controversy regarding the selection of candidates for the drug holiday and monitoring during a drug holiday, both of which should be based on individual assessments of risk and benefit. This statement will provide suggestions for clinicians in South Korea on the identification of possible candidates and monitoring during a bisphosphonate drug holiday.

Atypical femur fracture during bisphosphonate drug holiday: a case series

Recent studies have noted an increased risk of low energy subtrochanteric and femoral shaft fractures termed "atypical femur fractures" (AFFs) associated with long-term bisphosphonate use. As such, many clinicians have begun recommending a "drug holiday" to reduce the risks associated with long-term bisphosphonate use. We present two cases of AFFs occurring during a 4-year or greater drug holiday following long-term bisphosphonate use. These findings highlight the need to reevaluate optimal bisphosphonate therapy duration, dosage, as well as initiation and duration of a drug holiday with continued monitoring in the prevention of AFFs.

HIF targets in bone remodeling and metastatic disease

The bone marrow is a hypoxic microenvironment that is rich in growth factors and blood vessels and is readily colonized by tumor cells disseminated from numerous cancers including tumors of the breast, prostate, lung, and skin. The origin of metastatic growth promoting factors for tumor cells disseminated to the bone marrow is derived from multiple sources: the bone matrix, which is a reservoir for growth factors, and cells residing in the marrow and along bone surfaces, such as osteoblasts, osteoclasts, macrophages, and T cells, which secrete cytokines and chemokines. Low oxygen levels within the bone marrow induce hypoxia signaling pathways such as hypoxia inducible factor (HIF), which is regulated by oxygen requiring prolyl hydroxylases (PHDs) and von Hippel-Lindau (VHL) tumor suppressor. These hypoxia signaling pathways have profound effects on bone development and homeostasis. Likewise, hypoxic conditions observed in local breast and prostate tumors point to a role for hypoxia-inducible genes in metastasis to and colonization of the bone marrow. This review will explore the role of hypoxia-regulated factors in bone development and remodeling, and how these elements may contribute to solid tumor metastasis to the bone.

Questioning the association between bisphosphonates and atypical femoral fractures

Bisphosphonates are the first-line treatment for osteoporosis. Structurally, they are stable analogues of pyrophosphate and therefore exhibit a high affinity for bone mineral. They reduce bone loss by attenuating the ability of the osteoclast to resorb bone, decreasing activation frequency, and the rate of remodeling. Large prospective randomized placebo-control trials provide unequivocal evidence for a reduction in the incidence of fractures. Impressively, 40 years since their first use in patients, the safety profile of bisphosphonates has been equally reassuring. Questions have arisen lately as to whether bisphosphonates could cause atypical fractures, a rare type of atraumatic or minimal trauma femur fracture occurring below the great trochanter. This question has prompted calls for a broader examination of the long-term effects of bisphosphonate use. An attempt by the Food and Drug Administration to garner consensus and provide definitive views was not successful. This has led to continued anxiety among treating physicians and patients alike, resulting in an overall reduction in prescriptions for bisphosphonates and for osteoporosis therapies in general. Here, we provide an overview of the current data on atypical fractures and bisphosphonate use.

Inhibition of bone resorption by the cathepsin K inhibitor odanacatib is fully reversible

The cathepsin K (CatK) inhibitor odanacatib (ODN) is currently being developed for the treatment of osteoporosis. In clinical trials, efficacy and resolution of effect of ODN treatment on bone turnover biomarkers and accrued bone mass have been demonstrated. Here, we examine the effects of continuing treatment and discontinuation of ODN versus alendronate (ALN) on osteoclast (OC) function. First, accessibility and reversible engagement of active CatK in intracellular vesicles and resorption lacunae of actively resorbing OCs were demonstrated by the selective and reversible CatK inhibitors, BODIPY-L-226 (IC50=39nM) and L-873,724 (IC50=0.5nM). Next, mature human OCs on bone slices were treated with vehicle, ODN, or ALN for 2days, followed by either continuing with the same treatment, or replacement of the inhibitors by vehicle for additional times as specified per experimental conditions. Maintaining OCs on ODN or ALN significantly reduced CTx-I release compared to vehicle controls. However, only the treatment of OCs with ODN resulted in the formation of small shallow discrete resorption pits, retention of intracellular vesicles enriched with CatK and other lysosomal enzymes, increase in 1-CTP release and number of TRAP(+) OCs. Upon discontinuation of ODN treatment, OCs rapidly resumed bone resorption activity, as demonstrated by a return of OC functional markers (CTx-I, 1-CTP), cell number and size, morphology and number of resorption pits, and vesicular secretion of CatK toward the respective vehicle levels. As expected, discontinuation of ALN did not reverse the treatment-related inhibition of OC activity in the time frame of the experiment. In summary, this study demonstrated rapid kinetics of inhibition and reversibility of the effects of ODN on OC bone resorption, that differentiated the cellular mechanism of CatK inhibition from that of the bisphosphate antiresorptive ALN.

Use of drug holidays in women taking bisphosphonates

Bisphosphonates are the cornerstone of treatment for osteoporosis. These agents are generally safe and well-tolerated, but concerns have emerged about adverse effects related to long-term use, namely osteonecrosis of the jaw and atypical femur fractures. For most patients at moderate or high risk of fracture, the benefits of treatment far outweigh these serious but rare risks. Bisphosphonates accumulate in bone with some persistent protective effect after therapy is stopped, making it is reasonable to consider a "drug holiday." The duration of therapy and the length of the holiday should be based on clinical judgment.

Bisphosphonate long-term treatment related bilateral subtrochanteric femoral fracture. Can teriparatide be useful?

Long-term treatment with bisphosphonates has been related to atypical femoral fractures. We report the clinical case of a woman who suffered a proximal diaphyseal oblique fracture of the left femur after uninterrupted 13-year treatment with alendronate. Shortly after surgery, a painful lytic image in the external cortex of her right femur diaphysis was detected. Some papers have suggested surgical treatment to repair femur fractures after long-term treatment with bisphosphonates. Otherwise, two studies have shown healing acceleration of bone fractures with teriparatide. A lytic lesion was treated with teriparatide obtaining progressive disappearance of symptoms as well as bone healing. This outcome may suggest a way of prevention of complete fractures in symptomatic patients with long-term treatment with bisphosphonates.

Bisphosphonate drug holiday: who, when and how long

Bisphosphonates have been widely used in the treatment of osteoporosis with robust data from numerous placebo-controlled trials demonstrating efficacy in fracture risk reduction over 3-5 years of treatment. Although bisphosphonates are generally safe and well tolerated, concerns have emerged about adverse effects related to long-term use. For most patients with osteoporosis, the benefits of treatment outweigh the risks. Because these agents accumulate in bone with some persistent antifracture efficacy after therapy is stopped, it is reasonable to consider a 'drug holiday.' There is considerable controversy regarding the optimal duration of therapy and the length of the holiday, both of which should be based on individual assessments of risk and benefit.

Bisphosphonate drug holiday: choosing appropriate candidates

Osteoporosis related fractures contribute to morbidity and mortality in U.S. patients, placing a heavy financial burden on society. Randomized clinical trials involving over 30,000 subjects have established bisphosphonates' efficacy in reducing the incidence of fragility fractures. However, as bisphosphonates are retained for years in the skeleton, reports of adverse events from prolonged use are surfacing in the literature, namely, esophageal cancer, atrial fibrillation, osteonecrosis of the jaw, and atypical fracture development. The concept of a drug holiday has been proposed to potentially reduce incidence of these adverse events. This review will highlight the benefits and risks of bisphosphonate therapy and discuss the extension data available from the bisphosphonate trials. As randomized clinical trial evidence is not yet available on who may qualify for drug holiday, this review will provide suggestions for clinicians on identification of possible candidates and monitoring during a bisphosphonate drug holiday.

Atypical subtrochanteric femoral shaft fractures: role for mechanics and bone quality

Bisphosphonates are highly effective agents for reducing osteoporotic fractures in women and men, decreasing fracture incidence at the hip and spine up to 50%. In a small subset of patients, however, these agents have recently been associated with 'atypical femoral fractures' (AFFs) in the subtrochanteric region or the diaphysis. These fractures have several atypical characteristics, including occurrence with minimal trauma; younger age than typical osteoporotic fractures; occurrence at cortical, rather than cancellous sites; early radiographic appearance similar to that of a stress fracture; transverse fracture pattern rather than the familiar spiral or transverse-oblique morphologies; initiation on the lateral cortex; and high risk of fracture on the contralateral side, at the same location as the initial fracture. Fracture is a mechanical phenomenon that occurs when the loads applied to a structure such as a long bone exceed its load-bearing capacity, either due to a single catastrophic overload (traumatic failure) or as a result of accumulated damage and crack propagation at sub-failure loads (fatigue failure). The association of AFFs with no or minimal trauma suggests a fatigue-based mechanism that depends on cortical cross-sectional geometry and tissue material properties. In the case of AFFs, bisphosphonate treatment may alter cortical tissue properties, as these agents are known to alter bone remodeling. This review discusses the use of bisphosphonates, their effects on bone remodeling, mechanics and tissue composition, their significance as an effective therapy for osteoporosis, and why these agents may increase fracture risk in a small population of patients.

Inositol hexakisphosphate inhibits osteoclastogenesis on RAW 264.7 cells and human primary osteoclasts

BACKGROUND

Inoxitol hexakisphosphate (IP6) has been found to have an important role in biomineralization and a direct effect inhibiting mineralization of osteoblasts in vitro without impairing extracellular matrix production and expression of alkaline phosphatase. IP6 has been proposed to exhibit similar effects to those of bisphosphonates on bone resorption, however, its direct effect on osteoclasts (OCL) is presently unknown.

METHODOLOGY/PRINCIPAL FINDINGS

The aim of the present study was to investigate the effect of IP6 on the RAW 264.7 monocyte/macrophage mouse cell line and on human primary osteoclasts. On one hand, we show that IP6 decreases the osteoclastogenesis in RAW 264.7 cells induced by RANKL, without affecting cell proliferation or cell viability. The number of TRAP positive cells and mRNA levels of osteoclast markers such as TRAP, calcitonin receptor, cathepsin K and MMP-9 was decreased by IP6 on RANKL-treated cells. On the contrary, when giving IP6 to mature osteoclasts after RANKL treatment, a significant increase of bone resorption activity and TRAP mRNA levels was found. On the other hand, we show that 1 µM of IP6 inhibits osteoclastogenesis of human peripheral blood mononuclear cells (PBMNC) and their resorption activity both, when given to undifferentiated and to mature osteoclasts.

CONCLUSIONS/SIGNIFICANCE

Our results demonstrate that IP6 inhibits osteoclastogenesis on human PBMNC and on the RAW264.7 cell line. Thus, IP6 may represent a novel type of selective inhibitor of osteoclasts and prove useful for the treatment of osteoporosis.

Regional bone metabolism at the lumbar spine and hip following discontinuation of alendronate and risedronate treatment in postmenopausal women

The aim of this study was to examine the effects of bisphosphonate discontinuation on bone metabolism at the spine and hip measured using (18) F-fluoride PET. Bone metabolism at the spine remained stable following discontinuation of alendronate and risedronate at 1 year but increased in the hip in the alendronate group only.

INTRODUCTION

Bisphosphonates such as alendronate (ALN) or risedronate (RIS) have persistent effects on spine BMD following discontinuation.

METHODS

Positron emission tomography (PET) was used to examine regional bone metabolism in 20 postmenopausal women treated with ALN (n = 11) or RIS (n = 9) for a minimum of 3 years at screening (range 3-9 years, mean 5 years for both groups). Subjects underwent a dynamic scan of the lumbar spine and a static scan of both hips at baseline and 6 and 12 months following treatment discontinuation. (18) F-fluoride plasma clearance (K(i)) at the spine was calculated using a three-compartment model. Standardised uptake values (SUV) were calculated for the spine, total hip, femoral neck and femoral shaft. Measurements of BMD and biochemical markers of bone turnover were also performed.

RESULTS

With the exception of a significant decrease in spine BMD in the ALN group, BMD remained stable. Bone turnover markers increased significantly from baseline by 12 months for both study groups. Measurements of K(i) and SUV at the spine and femoral neck did not change significantly in either group. SUV at the femoral shaft and total hip increased significantly but in the ALN group only, increasing by 33.8% (p = 0.028) and 24.0% (p = 0.013), respectively.

CONCLUSIONS

Bone metabolism at the spine remained suppressed following treatment discontinuation. A significant increase in SUV at the femoral shaft and total hip after 12 months was observed but for the ALN group only. This study was small, and further clinical studies are required to fully evaluate the persistence of BP treatment.

Atypical femoral fractures and bisphosphonate treatment

We performed a retrospective review of all patients admitted to two large University Hospitals in the United Kingdom over a 24-month period from January 2008 to January 2010 to identify the incidence of atypical subtrochanteric and femoral shaft fractures and their relationship to bisphosphonate treatment. Of the 3515 patients with a fracture of the proximal femur, 156 fractures were in the subtrochanteric region. There were 251 femoral shaft fractures. The atypical fracture pattern was seen in 27 patients (7%) with 29 femoral shaft or subtrochanteric fractures. A total of 22 patients with 24 atypical fractures were receiving bisphosphonate treatment at the time of fracture. Prodromal pain was present in nine patients (11 fractures); 11 (50%) of the patients on bisphosphonates suffered 12 spontaneous fractures, and healing of these fractures was delayed in a number of patients. This large dual-centre review has established the incidence of atypical femoral fractures at 7% of the study population, 81% of whom had been on bisphosphonate treatment for a mean of 4.6 years (0.04 to 12.1).

This study does not advocate any change in the use of bisphosphonates to prevent fragility fractures but attempts to raise awareness of this possible problem so symptomatic patients will be appropriately investigated. However, more work is required to identify the true extent of this new and possibly increasing problem.

Use of bisphosphonate and risk of atrial fibrillation in older women with osteoporosis

Concerns have been raised among clinicians and patients whether or not bisphosphonates increase the risk of atrial fibrillation. In this large cohort study, increased risk of atrial fibrillation was not found to be associated with bisphosphonate. In fact, bisphosphonate even showed a protective effect against cardiac arrhythmia compared to other osteoporosis medications.

INTRODUCTION

Increased risk of atrial fibrillation among bisphosphonate users has been reported; however, the results from these studies are controversial. The purpose of this study was to evaluate the risk of atrial fibrillation associated with bisphosphonate use in older women.

METHODS

We used the Korean Health Insurance Review and Assessment Service claims database from May 1, 2005 to June 30, 2006. Retrospective cohort analysis was conducted on women 65 years or older with newly diagnosed cases of osteoporosis (ICD 10 code: M80, M81) who had not previously taken any medications for osteoporosis. Bisphosphonate-exposed and non-exposed patients were followed until they were either diagnosed with atrial fibrillation (ICD 10 code: I48) or until the end of the study. The Cox proportional hazards model was used to calculate hazard ratios and the 95% confidence intervals.

RESULTS

Atrial fibrillation was reported in 626 of the 120,319 patients (0.52%) treated with bisphosphonates and 66 of 9,863 patients (0.67%) treated with other osteoporosis medications. Overall hazard ratio for developing atrial fibrillation in the bisphosphonate-treated group was 0.52 (95% CIs, 0.29-0.91). In patients with a medication possession ratio greater than 0.7, the hazard ratio was lower (HR 0.41, 95% CIs 0.23-0.75). In the subgroup analysis, alendronate showed a statistically significant protective effect against the risk of atrial fibrillation with a hazard ratio of 0.75 (95% CI, 0.58-0.97).

CONCLUSION

Among older Korean women with osteoporosis, bisphosphonate was found to have a protective effect against atrial fibrillation.

Final results of the DAPS (Denosumab Adherence Preference Satisfaction) study: a 24-month, randomized, crossover comparison with alendronate in postmenopausal women

The final analysis of this 2-year, randomized, crossover study showed that postmenopausal women with osteoporosis were more adherent, compliant, and persistent with subcutaneous denosumab injections every 6 months than with once-weekly alendronate tablets. After receiving both treatments, women reported greater satisfaction with injectable denosumab and preferred it over oral alendronate.

INTRODUCTION

Osteoporosis patients who are non-compliant or non-persistent with therapy may have suboptimal clinical outcomes. This 2-year, randomized, open-label, crossover study compared treatment adherence between subcutaneous denosumab, 60 mg every 6 months, and oral alendronate, 70 mg once weekly.

METHODS

Postmenopausal women at 25 centers in the USA and Canada with bone mineral density T-scores -4.0 to -2.0 and no prior bisphosphonate use received alendronate then denosumab, or denosumab then alendronate, over successive 12-month periods. Adherence required both compliance (denosumab injections 6 months apart or ≥ 80% of alendronate tablets) and persistence (both denosumab injections or ≥ 2 alendronate doses in the last month and completion of the treatment period).

RESULTS

Of the 250 women enrolled (124 alendronate, 126 denosumab), 221 entered the second year (106 denosumab, 115 alendronate). Denosumab was associated with less non-adherence than alendronate (first year, 11.9% vs 23.4%; second year, 7.5% vs 36.5%). Risk ratios for non-adherence, non-compliance, and non-persistence favored denosumab in both years (p < 0.05). Of 198 subjects expressing treatment preference, 183 (92.4%) preferred the injections over the oral therapy. BMD improved further when subjects received denosumab after alendronate and remained stable when they received alendronate after denosumab.

CONCLUSION

Based on the final results of this crossover study after women had received each treatment for up to 1 year, postmenopausal women with osteoporosis were more adherent, compliant, and persistent with subcutaneous denosumab injections every 6 months than with once-weekly alendronate tablets and reported increased treatment preference and satisfaction with injectable denosumab over oral alendronate.

The effect of long-term alendronate treatment on cortical thickness of the proximal femur

BACKGROUND

One of the radiographic hallmarks in patients with atypical femoral insufficiency fractures after prolonged bisphosphonate treatment is generalized cortical hypertrophy. Whether cortical thickening in the proximal femur is caused by long-term alendronate therapy, however, remains unknown.

QUESTIONS/PURPOSES

We asked whether long-term alendronate use of 5 years or more results in progressive thickening of the subtrochanteric femoral cortices.

PATIENTS AND METHODS

We retrospectively evaluated changes in cortical thickness and cortical thickness ratio (ratio of cortical to femoral shaft diameter) at the subtrochanteric region of the proximal femur in baseline and latest hip dual-energy xray absorptiometry (DXA) scans of 131 patients. The mean followup was 7.3 years. Patients were divided into two groups: control (no history of alendronate, 45 patients) and alendronate (history of alendronate ≥ 5 years, 86 patients). We determined cortical thickness and cortical thickness ratio at 3.5 and 4.0 cm below the tip of the greater trochanter, representing the subtrochanteric region.

RESULTS

After a minimum of 5 years followup, mean cortical thickness decreased approximately 3% in the alendronate and control groups. The cortical thickness at the subtrochanteric femoral region changed less than 1 mm in greater than 90% of the patients with long-term alendronate treatment. We observed no differences in mean changes of cortical thickness and percent changes of cortical thickness between the two groups.

CONCLUSIONS

Long-term alendronate treatment did not appear to cause thickened femoral cortices within the detection limits of our method. This finding contrasts with the notion that long-term alendronate treatment leads to generalized cortical thickening.

Long-term bisphosphonate usage and subtrochanteric insufficiency fractures: a cause for concern?

For over a decade, bisphosphonate administration has evolved and become the cornerstone of the prevention and treatment of fragility fractures. Millions of post-menopausal women have relied on, and continue to depend on, the long-acting, bone density-maintaining pharmaceutical drug to prevent low-energy fractures. In return, we have seen the number of fragility fractures decrease, along with associated costs and emotional benefits. However, with any drug, there are often concerns with side effects and complications, and this unique drug class is seeing one such complication in atypical subtrochanteric femoral fracture, counterproductive to that which it was designed to prevent. This has created concern over long-term bisphosphonate administration and its potential link to these atypical fractures. There is controversial evidence surrounding such a definitive link, and no protocol for managing these fractures. This review offers the latest information regarding this rare but increasingly controversial adverse effect and its potential connection to one of the most successful forms of treatment that is available for the management of fragility fractures.

[Optimizing orthodontic treatment in patients taking bisphosphonates]

Bisphosphonates have unique pharmacological characteristics unlike those of any other drug group. Millions of adults take oral bisphosphonates for long-term treatment of osteoporosis and osteopenia; some of these people will most likely also seek orthodontic treatment. Adverse dental effects from bisphosphonates have been reported, including decreased tooth movement, impaired bone healing, and osteonecrosis in the mandible and the maxilla. Osteonecrosis has been rarely observed after bisphosphonate use for osteoporosis. However, adverse drug effects might occur more frequently in orthodontic patients, and they would probably be noted before the end-stage pathology of osteonecrosis. Adverse effects during orthodontic treatment, including decreased tooth movement, could last for years after the drug therapy is stopped. Successful orthodontic treatment requires optimal bone healing to prevent excessive tooth mobility. Bisphosphonates appear to have two bone elimination rates - a fast elimination of weeks from the bone surface and a slow elimination of years after incorporation into the bone structure. This article presents methods to clinically and radiographically monitor orthodontic patients who are taking oral bisphosphonates. Efforts to minimize adverse effects and optimize orthodontic procedures with physician-approved drug holidays are discussed. The orthodontic treatment results of three patients who received bisphosphonate therapy are reported.

Post-hip fracture use of prescribed calcium plus vitamin D or vitamin D supplements and antiosteoporotic drugs is associated with lower mortality: a nationwide study in Finland

We previously found a positive association between calcium plus vitamin D and antiosteoporotic drugs and survival among hip fracture patients. Our aim was to verify this observation using a nationwide database. A retrospective cohort of home-discharged hip fracture patients aged 50 years or older (n = 23,615) was enrolled from the national database. Primary exposure was medical treatment for osteoporosis, and the outcome was all-cause mortality. Cumulative mortalities were calculated using the Kaplan-Meier estimator. The relationship between mortality and medication purchases was modeled using Cox's proportional hazards regression with time-dependent covariates for medication use. One in 4 women and 1 in 10 men with a hip fracture were treated for osteoporosis in Finland. Unadjusted 1-year mortality was lower among patients who purchased calcium plus vitamin D or vitamin D supplements and antiosteoporotic drugs than among those who did not purchase these medications [hazard ratio (HR) = 0.74, 95% confidence interval (CI) 0.67-0.81]. The difference in unadjusted cumulative mortality remained in favor of the drug users for at least 5 years. Among men, the use of calcium plus vitamin D or vitamin D supplements was associated with lower 1-year mortality even after adjustments for observed confounders (HR = 0.74, 95% CI 0.56-0.97). Among women, the use of antiosteoporotic drugs was associated with lower mortality (HR = 0.79, 95% CI 0.67-0.93). There was a tendency to even better survival in both genders if calcium plus vitamin D or vitamin D supplements and antiosteoporotic drugs were used simultaneously, the HR being 0.72 (95% CI 0.50-1.03) in men and 0.62 (95% CI 0.50-0.76) in women.

Bisphosphonates for postmenopausal osteoporosis

Bisphosphonates are effective in reducing bone turnover, increasing BMD and reducing fracture risk in postmenopausal women with osteoporosis. The licensed bisphosphonates exhibit some differences in potency and speed of onset and offset of action. These differences mean that different agents may be more advantageous in different situations. Uncertainties still exist around the optimum duration of treatment and treatment holidays, how best to use bisphosphonates with anabolic treatments, and the benefits of treatment in patients who do not have a BMD T-score below -2.5.

Denosumab and bisphosphonates: different mechanisms of action and effects

To treat systemic bone loss as in osteoporosis and/or focal osteolysis as in rheumatoid arthritis or periodontal disease, most approaches target the osteoclasts, the cells that resorb bone. Bisphosphonates are currently the most widely used antiresorptive therapies. They act by binding the mineral component of bone and interfere with the action of osteoclasts. The nitrogen-containing bisphosphonates, such as alendronate, act as inhibitors of farnesyl-pyrophosphate synthase, which leads to inhibition of the prenylation of many intracellular signaling proteins. The discovery of RANKL and the essential role of RANK signaling in osteoclast differentiation, activity and survival have led to the development of denosumab, a fully human monoclonal antibody. Denosumab acts by binding to and inhibiting RANKL, leading to the loss of osteoclasts from bone surfaces. In phase 3 clinical studies, denosumab was shown to significantly reduce vertebral, nonvertebral and hip fractures compared with placebo and increase areal BMD compared with alendronate. In this review, we suggest that the key pharmacological differences between denosumab and the bisphosphonates reside in the distribution of the drugs within bone and their effects on precursors and mature osteoclasts. This may explain differences in the degree and rapidity of reduction of bone resorption, their potential differential effects on trabecular and cortical bone, and the reversibility of their actions.