Denosumab is a potent antiresorptive agent that substantially increases bone mineral density and reduces fracture rates at all skeletal sites for as long as it is administered. However, its favorable skeletal effects reverse quickly upon its discontinuation, because of a vast increase of osteoclast number and activity, which leads to a subsequent profound increase of bone turnover above pre-treatment values, a phenomenon commonly described as “rebound phenomenon”. More importantly, most patients experience rapid, profound bone loss due to this burst of bone resorption that may lead in a minority of these patients to occurrence of fractures, especially multiple vertebral fractures. Therefore, subsequent antiresorptive treatment is mandatory, although the optimal regimen is yet to be clarified. In the present review, we outline what is currently known regarding the negative effects of denosumab discontinuation on different aspects of bone status, the factors that may affect them, and strategies to prevent them.

Cessation of denosumab treatment is associated with increases in bone turnover above baseline values and rapid bone loss. We investigated the efficacy of zoledronate to prevent this bone loss in women with postmenopausal osteoporosis who were treated with denosumab (mean duration 2.2 years) and discontinued treatment after achieving osteopenia. Women were randomized to receive a single 5-mg infusion of zoledronate (ZOL) (n = 27) or two additional 60-mg injections of denosumab (Dmab) (n = 30). Both groups were followed for a total period of 24 months. At 24 months lumbar spine–bone mineral density (LS-BMD) was not different from baseline in the ZOL group, but decreased in the Dmab group by (mean ± SD) 4.82% ± 0.7% (p < 0.001) from the 12-month value; the difference in BMD changes between the two groups, the primary endpoint of the study, was statistically significant (p = 0.025). Results of femoral neck (FN)-BMD changes were similar. ZOL infusion was followed by small but significant increases in serum procollagen type 1 N-terminal propeptide (P1NP) and C-terminal telopeptide of type 1 collagen (CTX) during the first year and stabilization thereafter. In the Dmab group, bone turnover marker values did not change during the first 12 months but increased significantly at 15 months and in the majority of women these remained elevated at 24 months. Neither baseline nor 12-month bone turnover marker values were associated with BMD changes in either group of women. In the Dmab group, three patients sustained vertebral fractures (two patients multiple clinical, one patient morphometric) whereas one patient in the ZOL group sustained clinical vertebral fractures 12 months after the infusion. In conclusion, a single intravenous infusion of ZOL given 6 months after the last Dmab injection prevents bone loss for at least 2 years independently of the rate of bone turnover. Follow-up is recommended, because in a few patients ZOL treatment might not have the expected effect at 2 years. © 2019 American Society for Bone and Mineral Research.

Context Antiresorptive therapy significantly reduces fracture risk in patients with benign bone disease and skeletal-related events (SREs) in patients with bone metastases (BM). Osteonecrosis of the jaw (ONJ) is a rare but severe condition manifested as necrotic bone lesion or lesions of the jaws. ONJ has been linked to the use of potent antiresorptive agents, termed medication-related ONJ (MRONJ). Objective We aimed to identify the differences various aspects of MRONJ among distinct patient categories and provide recommendations on how to mitigate the risk and optimally manage MRONJ in each of them. Methods A working group of the European Calcified Tissue Society (ECTS) and 2 experts performed an updated detailed review of existing literature on MRONJ incidence, characteristics, and treatment applied in bone diseases with variable severity of skeletal insult, ranging from osteoporosis to prevention of cancer treatment–induced bone loss and SREs in cancer patients with BM. Results The risk for MRONJ is much higher in patients with advanced malignancies compared to those with benign bone diseases because of the higher doses and more frequent administration of antiresorptive agents in individuals with compromised general health, along with coadministration of other medications that predispose to MRONJ. The overall risk for MRONJ is considerably lower than the benefits in all categories of patients. Conclusion The risk for MRONJ largely depends on the underlying bone disease and the relevant antiresorptive regimen applied. Physicians and dentists should keep in mind that the benefits of antiresorptive therapy far outweigh the risk for MRONJ development.

The most widely used medications for the treatment of osteoporosis are currently bisphosphonates (BPs) and denosumab (Dmab). Both are antiresorptives, thus targeting the osteoclast and inhibiting bone resorption. Dmab achieves greater suppression of bone turnover and greater increases of bone mineral density (BMD) at all skeletal sites, both in naïve and pretreated patients. No superiority on fracture risk reduction has been documented so far. In long-term administration, BPs reach a plateau in BMD response after 2–3 years, especially at the hip, while BMD increases progressively for as long as Dmab is administered. Both BPs and Dmab are generally considered safe, although they have been correlated to rare adverse events, such as osteonecrosis of the jaw and atypical femoral fractures. Dmab should be preferred in patients with impaired renal function. BPs are embedded in the bone, from which they are slowly released during bone remodeling, therefore continuing to act for years after their discontinuation. In contrast, Dmab discontinuation fully and rapidly reverses its effects on bone markers and BMD and increases the risk for fractures; therefore, Dmab discontinuation should be discouraged, especially in previously treatment-naïve patients, regardless of the conventional fracture risk. In case of discontinuation, other treatment, mainly BPs, should immediately follow, although the optimal sequential treatment strategy is yet to be defined. Combination of teriparatide with Dmab or zoledronic acid, but not alendronate, provides increased BMD gains at all sites. In conclusion, both BPs and Dmab are safe and efficient therapeutic options although their particularities should be carefully considered in an individual basis.