VANCOUVER –
A previous head-to-head comparison showed that denosumab increased bone mineral density at key skeletal sites compared with zoledronic acid, but only a single, small observational study has examined fracture risk, and it found no difference.
The new study, presented at the annual meeting of the American Society for Bone and Mineral Research, used a relatively new method of real-world comparative effectiveness analysis called negative control outcome (NCO) to analyze Medicare fee-for-service data.
NCO analysis takes extra pains to remove bias through data that might be linked to potential confounders but could not reasonably be attributed to a drug. For example, people who have greater contact with the health care system may be more likely to get one drug or another. The researchers used the frequency of receiving a flu or pneumonia vaccine as a proxy for this. If the two comparison groups had a significant difference in a proxy, it suggested a hidden bias and forced the researchers to abandon those groupings. Another example used car accidents as a proxy for cognitive impairment.
“If you find meaningful differences between the two groups, and you can say there’s no way a bone drug could account for these differences, then we shouldn’t do this analysis because these groups just aren’t comparable. They probably differ by that confounding factor we couldn’t measure,” said Jeffrey Curtis, MD, who presented the study. He is a professor of medicine in the division of clinical immunology and rheumatology at the University of Alabama at Birmingham.
The study strongly suggests superiority for denosumab. “There was a significant difference in multiple different groupings of fractures – beginning at year 2, extending to year 3 and even out to year 5 – that showed that there is a significant reduction in fracture risk if you get treated with denosumab [that was greater] than if you get treated with zoledronic acid,” Dr. Curtis said.
The researchers weighed 118 covariates and ultimately identified a population of 90,805 women taking denosumab and 37,328 taking zoledronic acid that was equally balanced in all patient characteristics. The mean age was about 75 years in the denosumab group and 74 in the zoledronic acid group.
The researchers found a 34% lower risk for hip fracture in the denosumab group by 5 years (relative risk, 0.66; 95% confidence interval, 0.43-0.90).
Similar patterns in fracture risk reduction were observed at 5 years for nonvertebral fracture (RR, 0.67; 95% CI, 0.52-0.82), nonhip nonvertebral fracture (RR, 0.69; 95% CI, 0.50-0.88), and major osteoporotic fracture (RR, 0.74; 95% CI, 0.59-0.89).
During the Q&A session after the talk, one audience member commented that the study was limited because the researchers only followed patients who received zoledronic acid for 60 days, which could have missed potential long-term benefits of the drug, especially since bisphosphonates have a lengthy skeletal retention time. Dr. Curtis acknowledged the point but said, “Usually, that’s not something we do, but these are different enough mechanisms of action that it may be warranted at least as a sensitivity analysis,” he said.
The study and its methodology were impressive, according to Yumie Rhee, MD, who comoderated the session where the study was presented. “I think they did a really good job by doing the negative control analysis. We’re not going to have a head-to-head clinical trial, so we don’t know the real fracture reduction differences [between denosumab and zoledronic acid]. [The NCO analysis] is more than the propensity matching score that we do usually,” said Dr. Rhee, who is a professor of endocrinology at Yonsei University College of Medicine in Seoul, South Korea.
In particular, the study showed a significantly greater reduction in hip fractures with denosumab. “Even in the RCTs, it was really hard to see the reduction in hip fracture, so I think this is showing much stronger data for denosumab. Especially in patients who have more [general fracture] risk and patients with higher hip fracture risk, I would go with denosumab,” Dr. Rhee said.
Her comoderator, Maria Zanchetta, MD, agreed. “It can have clinical implication, because we think denosumab is better than [zoledronic acid] for higher-risk patients, but we didn’t have the evidence. So at least we have a new [study] to look at, and I think it’s very important for our practice,” said Dr. Zanchetta, who is a professor of osteology at the Institute of Diagnostics and Metabolic Research, Universidad del Salvador, Buenos Aires.
The study was funded by Amgen, which markets denosumab. Dr. Curtis has consulted for Amgen. Dr. Rhee and Dr. Zanchetta report no relevant financial relationships.
A version of this article first appeared on Medscape.com.