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Published on: June 8, 2014
The relationship between changes in calcium concentration and bone mineral density by anti-bone resorptive therapy
Akira Horikawa1, Yuji Kasukawa2, Michio Hongo2
1Shizuoka Tokusyukai Hospital, 1-11 Surugaku-Simokawahara-Minami, Shizuoka 421-0117, Japan.
Background:
Hypocalcemia after initiating antiresorptive therapy is well documented, but the association between early changes in serum-corrected calcium (Ca) concentration and long-term bone mineral density (BMD) response in osteoporosis remains unclear. This study compared early Ca changes and BMD outcomes in patients treated with zoledronic acid or denosumab.
Methodology:
In this retrospective study, 67 outpatients with osteoporosis received either zoledronic acid (n = 25) or denosumab (n = 42). Baseline BMD, serum-corrected Ca concentration, bone turnover markers, estimated glomerular filtration rate (eGFR), and 25-hydroxyvitamin D [25(OH)D] were recorded. Serum-corrected Ca concentration and eGFR were reassessed at 1 week, 6 months, and 12 months and BMD was measured at baseline, 6 months, and 12 months. To prevent hypocalcemia, patients received different vitamin D regimens according to standard practice (active vitamin D3 for zoledronic acid and combined natural and active vitamin D for denosumab). Multivariate regression has been adjusted for age, baseline BMD, 25(OH)D, eGFR, and TRACP-5b.
Results:
A significant decrease in serum-corrected Ca at 1 week was observed in both groups. The magnitude of this decrease was negatively associated with lumbar spine BMD change at 12 months (zoledronic acid: r = -0.59, p = 0.0077; denosumab: r = -0.52, p = 0.0067). This association remained significant after multivariate adjustment. ROC analysis showed that Ca decrease predicted greater BMD gains (AUC 0.909 for zoledronic acid and AUC 0.81 for denosumab), but these results should be interpreted with caution due to the small sample size and different vitamin D regimens.
Conclusions:
Early decreases in serum-corrected Ca concentration after antiresorptive therapy were associated with greater BMD gains at 12 months, independent of baseline vitamin D, renal function, and bone turnover markers. This study is exploratory and preliminary in nature, and its findings should be interpreted with caution.
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