The long-term effects of switching from active intravenous bisphosphonate treatment to low-dose maintenance therapy in children with osteogenesis imperfecta

Background/Aims: Intravenous bisphosphonate therapy is the first-line treatment in moderate-to-severe osteogenesis imperfecta (OI), but there are varied treatment protocols with little data on long-term efficacy. This study evaluates the clinical outcomes when transitioning from active bisphosphonate treatment to maintenance therapy. Methods: A retrospective review was conducted on 17 patients before treatment, following active treatment (zoledronate 0.05 mg/kg 6-monthly or pamidronate 6-9 mg/kg/year) and after establishment on maintenance treatment for more than 2 years (zoledronate 0.025 mg/kg 6-monthly or pamidronate <4 mg/kg/year). Results: There was a significant reduction in mean fracture rate from 1.5 +/- 1.1 fractures/year at baseline to 0.7 +/- 0.7 fractures/year on active treatment. Z-scores for lumbar spine bone mineral density, bone mineral content, volumetric bone mineral density and bone mineral content for lean tissue mass increased during active treatment. These improvements were maintained during the period of maintenance treatment. Vertebral height improved in fractured thoracic vertebrae from pre-treatment to active therapy and improved further during maintenance treatment. Metacarpal cortical thickness and relative cortical area also increased over the treatment periods. Conclusion: Maintenance intravenous bisphosphonate therapy preserved the beneficial effects of active treatment at the doses stated above. Further studies are required to determine the optimal bisphosphonate treatment regimen in the management of children with OI.