Name: Sodium etidronate (Didronel)
Class: Bisphosphonate
Mechanism: Structure sim. to inorganic pyrophosphate. Impairs formation and dissolution of calcium phosphate crystals. Alters number/activity of osteoclasts (1° effect) ® slowed bone resorption. Slows formation and dissolution of hydroxyapatite crystals.
Absorp.: Oral ® very little absorp., but still effective. Oral absorp. varies w/dose. Further reduced by food or divalent cations. IV ® much higher blood levels.
Dist.: 50% of absorbed drug accum. in bone and turns over w/t½ of weeks.
Metabolism.:
Excretion, t½: 50% rapidly excreted unchanged by kidney.
Toxicity/S.E.s: Protracted or high-dose therapy ® osteomalacia.
Utility: Treat Paget’s disease of bone as well as or better than calcitonin—oral efficacy, lower cost, no antigenicity, longer remissions. However, chronic use ® osteomalacia w/risk of bone pain & fractures. Treat heterotopic ossification—given orally after total hip replacement or spinal injury. Treat hypercalcemia of malignancy (IV). Under testing for long-term intermittent therapy for vertebral osteoporosis (+ calcium and vit. D).