Unlabelled: This multicentre, retrospective case series analysed bone mineral density (BMD) changes in 26 patients who switched early from romosozumab (3-10 months) to antiresorptives. BMD gains over 12 months were similar to those in patients (n = 99) completing the full 12-month course.

Background: Romosozumab is typically administered for a duration of 12 months before transitioning to antiresorptive therapies. This study analysed the bone mineral density (BMD) changes of patients who were prematurely switched to an antiresorptive regimen.

Methods: This multicentre, retrospective case series investigated the BMD response to romosozumab administered for 3 to 10 months, followed by subsequent antiresorptive therapy, across four bone centres in Switzerland. BMD measurements at the lumbar spine, total hip and femoral neck were conducted at the initiation of romosozumab and again 12 months later. The study compared the BMD changes in patients who received short-term romosozumab with those in a cohort of patients who completed the full 12-month course.

Results: Twenty-six patients (25 postmenopausal women and one man, median age 73 years [interquartile range: 65, 81]) were enrolled from February 2022 to December 2024. They received a median of six romosozumab injections (range: 3 to 10) and were prematurely switched to antiresorptives (14 to denosumab, 11 to zoledronate and one to alendronate) due to possible side effects or adverse events. Over 12 months, BMD increased by 13.5% [8.6, 16.6] at the lumbar spine, 2.9% [0.3, 7.3] at the total hip and 3.2% [0.4, 7.8] at the femoral neck, without significant differences compared with the cohort of 99 patients who received 12 months of romosozumab therapy. In both the short- and full-duration romosozumab treatment groups, significantly lower BMD responses were observed in patients who were pretreated with antiresorptives compared with those who were treatment naïve.

Conclusion: In patients who underwent an early switch from romosozumab to antiresorptive therapy, BMD responses during the first year were similar to those in patients who completed the full 12-month romosozumab treatment. However, the subsequent changes in BMD, when all patients are receiving antiresorptive therapy, remain to be determined.