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Delaying denosumab dose boosts risk for vertebral fractures



Delaying doses of denosumab after the first injection dramatically boosts the risk that patients with osteoporosis will suffer vertebral fractures, a new study confirms. Physicians say they are especially concerned about the risk facing patients who are delaying the treatment during the coronavirus pandemic.

Female doctor showing to female senior patient in hospital an x-ray on the tablet doble-d/Getty Images

The recommended doses of denosumab are at 6-month intervals. Patients who delayed a dose by more than 16 weeks were nearly four times more likely to suffer vertebral fractures, compared with those who received on-time injections, according to the study, which was published in Annals of Internal Medicine.

“Because patients who used denosumab were at high risk for vertebral fracture, strategies to improve timely administration of denosumab in routine clinical settings are needed,” wrote the study authors, led by Houchen Lyu, MD, PhD, of National Clinical Research Center for Orthopedics, Sports Medicine & Rehabilitation at General Hospital of Chinese PLA in Beijing.

Denosumab, a human monoclonal antibody, is used to reduce bone loss in osteoporosis. The manufacturer of Prolia, a brand of the drug, recommends it be given every 6 months, but the study reports that it’s common for injections to be delayed.

Researchers have linked cessation of denosumab to higher risk of fractures, and Dr. Lyu led a study published earlier this year that linked less-frequent doses to less bone mineral density improvement. “However,” the authors of the new study wrote, “whether delaying subsequent injections beyond the recommended 6-month interval is associated with fractures is unknown.”

For their new study, researchers retrospectively analyzed data from 2,594 patients in the U.K. 45 years or older (mean age, 76; 94% female; 53% with a history of major osteoporotic fracture) who began taking denosumab between 2010 and 2019. They used a design that aimed to emulate a clinical trial, comparing three dosing intervals: “on time” (within 4 weeks of the recommended 6-month interval), “short delay” (within 4-16 weeks) and “long delay” (16 weeks to 6 months).

The study found that the risk of composite fracture over 6 months out of 1,000 was 27.3 for on-time dosing, 32.2 for short-delay dosing, and 42.4 for long-delay dosing. The hazard ratio for long-delay versus on-time was 1.44 (95% confidence interval, 0.96-2.17; P = .093).

Vertebral fractures were less likely, but delays boosted the risk significantly: Over 6 months, it grew from 2.2 in 1,000 (on time) to 3.6 in 1,000 (short delay) and 10.1 in 1,000 (long delay). The HR for long delay versus on time was 3.91 (95% CI, 1.62-9.45; P = .005).

“This study had limited statistical power for composite fracture and several secondary end points ... except for vertebral fracture. Thus, evidence was insufficient to conclude that fracture risk was increased at other anatomical sites.”

In an accompanying editorial, two physicians from the University of Minnesota, Minneapolis, noted that the study is “timely and relevant” since the coronavirus pandemic may disrupt dosage schedules more than usual. While the study has limitations, the “findings are consistent with known denosumab pharmacokinetics and prior studies of fracture incidence after denosumab treatment discontinuation, wrote Kristine E. Ensrud, MD, MPH, who is also of Minneapolis VA Health Care System, and John T. Schousboe, MD, PhD, who is also of HealthPartners Institute.

The editorial authors noted that, in light of the pandemic, “some organizations recommend temporary transition to an oral bisphosphonate in patients receiving denosumab treatment for whom continued treatment is not feasible within 7 to 8 months of their most recent injection.”

In an interview, endocrinologist and osteoporosis specialist Ethel Siris, MD, of Columbia University, New York, said many of her patients aren’t coming in for denosumab injections during the pandemic. “It’s hard enough to get people to show up every 6 months to get their shot when things are going nicely,” she said. “We’re talking older women who may be on a lot of other medications. People forget, and it’s difficult for the office to constantly remind some of them to get their shots at an infusion center.”

The lack of symptoms is another challenge to getting patients to return for doses, she said. “In osteoporosis, the only time something hurts is if you break it.”

Since the pandemic began, many patients have been avoiding medical offices because of fear of getting the coronavirus.

The new research is helpful because it shows that patients are “more likely to fracture if they delay,” Dr. Siris noted. The endocrinologist added that she has successfully convinced some patients to give themselves subcutaneous injections in the abdomen at home.

Dr. Siris said she has been able to watch patients do these injections on video to check their technique. Her patients have been impressed by “how easy it is and delighted to have accomplished it,” she said.

The study was funded by the National Institutes of Health China’s National Clinical Research Center for Orthopedics, Sports Medicine & Rehabilitation. The study authors, commentary authors, and Dr. Siris report no relevant disclosures.

SOURCE: Lyu H et al. Ann Intern Med. 2020 Jul 28. doi: 10.7326/M20-0882.

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