Purpose The occurrence of multiple vertebral fractures was reported after denosumab discontinuation. The use of bisphosphonates following denosumab has been suggested to prevent this bone loss. The aim of our observational trial was to evaluate the ability of risedronate to prevent the bone loss related to denosumab discontinuation in post-menopausal osteoporosis. Methods Eighteen female patients, aged 69.8 years (56–79), were followed. All patients were prescribed 35 mg of risedronate per week for 3 months, starting when the next denosumab injection would have been administered. We measured BMD at denosumab initiation (T0), denosumab withdrawal (T1), and nine months after the discontinuation of risedronate (1 year post-denosumab: T2). Results 1 year after denosumab discontinuation, the mean bone loss at the spine was – 4.6 ± 5.2% for the total population, −0.3 ± 2.3% in patients with prior exposure to bisphosphonates, −6.3 ± 5.7% in patients with prior exposure to teriparatide, and − 7.6 ± 3.5% in naïve patients. Spine BMD loss after the risedronate bridging therapy (T2 vs. T1) was significantly lower in patients who experienced prior exposure to bisphosphonates, when compared to naïve patients (p = .0190) and to patients with prior teriparatide exposure (p = .0176). 1 year after denosumab discontinuation, the mean densitometric loss at the hip was −1.8 ± 3.4% in the total cohort, −0.6 ± 1.8% in the patients previously treated with bisphosphonates, −1.5 ± 4.7% in the patients previously treated with teriparatide, and − 4.2 ± 0.6 in naïve patients. The mean densitometric loss during the off-denosumab period was lower in patients with previous bisphosphonate exposure than in naïve patients (p = .043) and in patients with previous exposure to teriparatide (p = .05). Conclusions Three months of risedronate treatment does not prevent bone loss in patients who have not been treated with bisphosphonates before denosumab.

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