title: Optimal timing of a single dose of zoledronic acid to increase strength in rat fracture repair.
abstract: We hypothesized that ZA treatment would bolster fracture repair. In a rat model for closed fracture healing, a single dose of ZA at 0, 1, or 2 wk after fracture significantly increased BMC and strength of the healed fracture. Delaying the dose (1 or 2 wk after fracture) displayed superior results compared with dosing at the time of fracture.
  
  
  BACKGROUND
  Bisphosphonates are known to increase bone strength and thus the resistance to fracture by decreasing osteoclastic bone resorption. These properties may enable bisphosphonates to also increase the strength of fracture repair. Zoledronic acid (ZA) is a potent bisphosphonate with a high affinity for bone mineral, allowing bolus intravenous dosing in a range of indications. In this study, we examined the application of bolus dose ZA in endochondral fracture repair.
  
  
  METHODS
  Carbon-14 labeled ZA was used in a closed rat fracture model. Rats were divided into five treatment groups (n = 25 per group): saline control, local ZA (0.01 mg/kg), and three systemic bolus ZA groups (0.1 mg/kg) with different administration times: at fracture, 1 wk after fracture, and 2 wk after fracture. Rats were killed 6 wk postoperatively. Postmortem analyses included radiography, QCT, microCT, biomechanical testing, scintillation counting, autoradiography, and histology.
  
  
  RESULTS
  Single-dose systemic ZA administration significantly increased callus volume, callus BMC, and mechanical strength. Perioperative treatment increased mechanical strength by 30% compared with controls (p < 0.05). Administering the systemic dose at 1 or 2 wk after fracture further increased mechanical strength compared with controls by 44% and 50%, respectively (p < 0.05). No significant differences in mechanical parameters were seen with local injection at the dose studied. Autoradiographic analysis indicated that ZA binds significantly to bone that is present at the time of administration. ZA quantification indicated that delayed administration significantly increased the uptake efficiency in the callus. Histological and microCT analysis showed that ZA treated calluses had a distinctive internal structure consisting of an intricate network of retained trabecular bone.
  
  
  CONCLUSIONS
  The timing of a single systemic dose of ZA plays an important role in the modulation of callus properties in this rat fracture model; delaying the single dose produces a larger and stronger callus.
authors: Orthopaedic Research and Biotechnology, The Children's Hospital at Westmead, Westmead, Australia.
authors: Negin
authors: N
authors: Amanat
authors: Michelle
authors: M
authors: McDonald
authors: Craig
authors: C
authors: Godfrey
authors: Lynne
authors: L
authors: Bilston
authors: David
authors: D
authors: Little
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D015519:Bone Density / Q000187:drug effects; D050071:Bone Density Conservation Agents / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology; D002146:Bony Callus / Q000737:chemistry / Q000187:drug effects; D002113:Calcification, Physiologic / Q000187:drug effects; D002452:Cell Count; D018483:Diaphyses / Q000737:chemistry / Q000293:injuries; D004164:Diphosphonates / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology*; D005264:Femoral Fractures / Q000188:drug therapy* / Q000503:physiopathology; D017102:Fracture Healing / Q000187:drug effects*; D007093:Imidazoles / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology*; D008297:Male; D010010:Osteoclasts / Q000166:cytology / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D014057:Tomography, X-Ray Computed; D019415:Torque; D000077211:Zoledronic Acid
chemical_list: D050071:Bone Density Conservation Agents; D004164:Diphosphonates; D007093:Imidazoles; D000077211:Zoledronic Acid