Bone Abstracts

Introduction: The availability of bone turnover markers (BTMs) that are kidney independent has facilitated the monitoring of bone turnover in renal patients with hyperparathyroid bone disease. The effects of Cinacalcet on BTMs and on the relationship between parathyroid hormone (PTH) and BTMs were studied.

Methods: The formation marker procollagen type 1 N propeptide (P1NP) and resorption marker tartrate resistant acid phosphatase 5b (TRACP5b) were measured before and at 14 time points during Cinacalcet treatment at doses of 30, 60, 90,120 and 150 mg/day over 20 months.

Results: P1NP increased from 196.7 to 361.2 μg/l at 6 months and 389.6 μg/l at 12 months when PTH was 576.7, 195.2 and 98.9 ng/l. P1NP decreased at each subsequent time point as PTH declined, reaching 89.5 μg/l when PTH was 24.7 ng/l.

TRACP5b decreased from 10.3 to 7.16 U/l at 6 months, 5.19 U/l at 12 months and 3.27 U/l at 20 months. There was significant negative correlation between PTH and P1NP(r=−0.69; P<0.05) when PTH >90.0 ng/l but no significant correlation when PTH <60 μg/l. Significant positive correlation was found between PTH and TRACP5b (r=0.7679; P<0.001) at all levels of PTH.

Conclusion: Increasing doses of Cinacalcet over a period of 20 months reduced PTH levels by 96%. Bone formation increased by 50% when PTH >90.0 ng/l but decreased thereafter by 77% when PTH <60.0 ng/l. Bone resorption overall decreased by 68%. The results suggest positive bone balance with increasing doses of Cinacalcet up to a PTH cut-off level of ~60.0 ng/l.