Summary:​ This phase 2 study evaluated the efficacy and safety of transitioning to zoledronate following romosozumab treatment in postmenopausal women with low bone mass. A single dose of 5 mg zoledronate generally maintained the robust BMD gains accrued with romosozumab treatment and was well tolerated.

Introduction:​ Follow-on therapy with an antiresorptive agent is necessary to maintain the skeletal benefits of romosozumab therapy. We evaluated the use of zoledronate following romosozumab treatment.

Methods:​ This phase 2, dose-finding study enrolled postmenopausal women with low bone mineral density (BMD). Subjects who received various romosozumab doses or placebo from months 0–24 were rerandomized to denosumab (60 mg SC Q6M) or placebo for 12 months, followed by open-label romosozumab (210 mg QM) for 12 months. At month 48, subjects who had received active treatment for 48 months were assigned to no further active treatment and all other subjects were assigned to zoledronate 5 mg IV. Efficacy (BMD, P1NP, and β-CTX) and safety were evaluated for 24 months, up to month 72.

Results:​ A total of 141 subjects entered the month 48–72 period, with 51 in the no further active treatment group and 90 in the zoledronate group. In subjects receiving no further active treatment, lumbar spine (LS) BMD decreased by 10.8% from months 48–72 but remained 4.2% above the original baseline. In subjects receiving zoledronate, LS BMD was maintained (percentage changes:​ − 0.8% from months 48–72;​ 12.8% from months 0–72). Similar patterns were observed for proximal femur BMD in both groups. With no further active treatment, P1NP and β-CTX decreased but remained above baseline at month 72. Following zoledronate, P1NP and β-CTX levels initially decreased but approached baseline by month 72. No new safety signals were observed.

Conclusion:​ A zoledronate follow-on regimen can maintain robust BMD gains achieved with romosozumab treatment.