Frank C Ko, Lamya Karim, Daniel J Brooks, Mary L Bouxsein, Marie B Demay

Bisphosphonates are being increasingly used to treat pediatric patients with skeletal disorders. However, the effects of long-term bisphosphonate therapy and cessation of therapy during growth are unclear. Thus, studies were undertaken to determine the effects of alendronate discontinuation following treatment of C57Bl/6 mice during the period of rapid skeletal growth. Compared to vehicle-treated mice, 16 weeks of alendronate treatment starting at 18 days of age resulted in a 3.7 fold increase in trabecular bone in the setting of suppressed bone formation. Alendronate therapy for 8 weeks followed by 8 weeks of vehicle treatment resulted in a more pronounced increase in trabecular bone compared to mice treated with alendronate for 16 weeks (1.7 fold) and to vehicle-treated controls (6.5 fold). Mice that received alendronate for 8 weeks followed by 8 weeks of vehicle exhibited increased osteoblast surface (2.5 fold), mineralizing surface (5.7 fold), and bone formation rate (5.1 fold) compared to mice treated continuously with alendronate. However, these parameters were not restored to the levels observed in the vehicle-treated mice. Thus, partial resumption of bone formation upon cessation of bisphosphonate therapy leads to a greater increase in trabecular bone than that seen when bisphosphonates are administered continuously to growing mice. These data suggest that intermittent administration of bisphosphonates may optimize their beneficial effects on the growing skeleton. This article is protected by copyright. All rights reserved.