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Pharmacological Therapy: Bisphosphonates

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Within weeks after SCI, there is a marked increase in bone resorption (breaking bone down) with a decrease in bone formation (adding new bone). These phenomena are responsible for the significant loss of bone mass that occurs after SCI. Bisphosphonates are a group of medications that are used to prevent declines in bone mass or treat low BMD; they act to slow down excessive bone resorption. They are generally divided into two types, those with or without nitrogen; each type has a different mechanism of action. Etidronate (Didrocal, Didronel), clodronate (Bonefos, Ostac) and tiludronate (Skelid) do not contain nitrogen while pamidronate (Aredia), alendronate (cholecalciferol, Fosamax, Fosamax Plus D, Fosavance), ibandronate (Boniva), risedronate (Actonel, Actonel with Calcium) and zoledronate (zoledronic acid, Aclasta, Reclast, Zomera, Zometa) contain nitrogen. Etidronate, alendronate and risedronate are oral bisphosphonates that are currently approved for the treatment of postmenopausal osteoporosis in Canada (Brown et al. 2002).  Clodronate is available intravenously (IV) and orally for the treatment of osteoporosis.  Tiludronate is available in oral form in the United States.  Zoledronate is a newer once yearly bisphosphonate which is administered via IV infusion.  Concurrent supplementation with calcium and vitamin D have been important additions to bisphosphonate therapy for post-menopausal osteoporosis (Brown et al. 2002). The concurrent administration of calcium, vitamin D, and bisphosphonates has not been prospectively evaluated in the SCI population, but should nonetheless be considered when prescribing oral bisphosphonates for SLOP based on the post-menopausal osteoporosis literature.