Zoledronate after denosumab discontinuation: Is repeated administrations more effective than single infusion?

Background After denosumab (Dmab) discontinuation C-terminal telopeptide (CTX) levels increase, bone mineral density (BMD) decreases and multiple vertebral fractures (FX) may occur with relevant impacts on women's health. A sequential therapy with bisphosphonates is recommended, and the European Calcified Tissue Society (ECTS) proposed repeated zoledronate (ZOL) administrations in patients with persistently high CTX levels, although the efficacy of this schedule is unknown. In this retrospective study, we describe BMD changes and FX rate in 52 patients managed according to the ECTS recommendations. Methods We measured CTX levels and administered ZOL after 1 month from Dmab withdrawal (t0). After 6 months (t1), we administered a second ZOL infusion, if CTX levels were >= 280 ng/L. BMD changes and FX rate were assessed on average after 17 months from Dmab withdrawal. Results Seventy-five percent of patients repeated ZOL infusion. In this group, spine BMD declined significantly (-5.5 +/- 5.6%), while it remained stable in the group with CTX levels <280 ng/L (-0.1 +/- 5.5%, P = 0.008). All fractured patients (9.6%) had received >5 Dmab injections and 2 ZOL infusions. The BMD worsening after Dmab withdrawal was associated with CTX t1 [odds ratio (OR) 2.9, interquartile range (IQR) 1.3-6.6, P = .009] and spine BMD gain during Dmab therapy corrected for the number of Dmab injections (OR 3.0, IQR 1.2-7.2, P = .014). A CTX level at t1 > 212 ng/L had 100% sensitivity in predicting the BMD loss. Conclusion In patients with uncontrolled CTX levels after Dmab withdrawal, 2 ZOL infusions 6 months apart do not prevent BMD loss and FX.