Background Bisphosphonates are first line therapy in the treatment Paget’s Disease (PD). The objective of this observational study was to assess short and long-term efficacy and safety of zoledronate in the treatment of active PD.

Methods Patients with active PD treated with zoledronate 5 mg were consecutively recruited and followed prospectively. Clinical and laboratory parameters (alkaline phosphatase (ALP), bone specific alkaline phosphatase (BSALP), procollagen type 1 N-terminal propeptide (P1NP), collagen type 1 beta C-terminal telopeptide (b-CTX), seric and urinary calcium and phosphorus and parathormone levels) were determined before, at 3 and every 6 months after treatment. Remission was defined as normalization of ALP. Retreatement was considered when ALP levels increased more than 25% of the upper limit of normal or of the nadir achieve in cases of non normalization of ALP. Adverse events were registered according to clinical protocol.

Results 60 patients (60% males), with a mean age of 68 ± 11 years and a mean disease duration of 11 ± 9 years were included. 69% had polyostotic disease and a mean percentage of skeletal involvement of 10.8 ± 7.6%. 68% were symptomatic: 71% of those referring bone and 54% joint pain attributed to PD. 48.3% had been previously treated with pamidronate (cumulative dose 234 ± 209 mg). The mean follow-up period after zoledronate infusion was of 37 ± 13 months. Only 4 patients (6.6%) required retreatment, on average 30 months after the first zoledronate infusion. A marked reduction of ALP) was observed at 3 (70%) and 6 months (74%) being maximal at 12 months (75%) (p < 0.001). At 3 and 6 months, 95% and 96% of patients respectively, achieved remission. Maximum effect was obtained at 12 months after treatment with 98% of patients being in remission. Significant reductions of the mean levels of BSALP, P1NP, and b-CTX (p < 0.001) were also verified at 3, 6 and 12 months after treatment. 47% of patients reported pain improvement: 89% at 3 months, 7% at 6 months and 4% at 12 months. Transitory side effects were registered in 15 patients, 18% referred flu-like symptoms, 10% showed asymptomatic hypocalcaemia and 30% asymptomatic hypophosphoremia.

Conclusions This study confirms the efficacy and safety of zoledronate in a Portuguese population of patients with active Paget’s disease. Biochemical remission was achieved in 98% of patients at 12 months and improvement of pain in 47%, the majority 3 months after treatment. Furthermore these benefits were long-term sustained with only 6.6% of patients requiring retreatment during an average follow-up of 37 months.