Bone Abstracts

Objectives: Cyclical intravenous pamidronate (PAM) and zoledronic acid (ZOL) increases bone mineral density (BMD) and reduces fractures in children with osteogenesis imperfecta (OI). The aims of this study were to evaluate fracture and BMD outcomes after treatment discontinuation in children with OI treated with ZOL compared to PAM.

Methods: 21 patients (mean age 5.1±3.8 years) received PAM (1 mg/kg per day x 3 days q 3 months for the first year). Seven patients (mean age 6±4.3 years) received ZOL (0.025 mg/kg/dose q 3 months for the first year). Frequency of infusions was decreased in subsequent years. Fractures and lumbar BMD (LBMD) z-scores were assessed at four time points: before treatment, before treatment discontinuation, 1 and 2 years after treatment discontinuation.

Results: There was a significant increase in LBMD z-score from baseline to before treatment discontinuation in both groups (from −2.7±1.8 to 0.3 1.6 in PAM; from −2.6±2.3 to 1.6±1.7 in ZOL). LBMD z-scores were maintained at 1 and 2 years after treatment discontinuation in both groups (0.8±1.8 and 1.0±1.4 in PAM; 0.9±2.6 and 1.7±1.8 in ZOL). While there was no significant difference in LBMD z-scores over time between two groups, the total number of infusions was significantly higher in PAM group than ZOL group (12.5±7.8 vs 6.1±2.5 infusions, P=0.02). Fracture rates decreased significantly during treatment in both groups (from baseline of 2.2±4.2 per year to 0.6±0.8 per year in PAM; from 1.9±2.9 per year to 0.3±0.5 per year in ZOL). After treatment discontinuation, fracture rates remained low in both groups (1.9±4.2 in PAM, 0.5±0.7 in ZOL).

Conclusions: PAM and ZOL were both effective therapy for children with OI, with sustained BMD improvement for 2 years after treatment discontinuation. However, fewer infusions were required in ZOL than PAM to achieve similar effects. These results suggest that ZOL had superior potency and efficacy to PAM. Further study is needed to evaluate long-term safety and efficacy of ZOL in patients with OI.

Disclosure: The authors declared no competing interests.