The effect of timing of teriparatide treatment on the circadian rhythm of bone turnover in postmenopausal osteoporosis.

BACKGROUND: We hypothesized that with the administration of teriparatide (TPTD) treatment at different times, we would be able to modify the physiological circadian rhythm of bone turnover. METHODS: The concentration of serum C-terminal telopeptide of collagen type I (ßCTX), serum N-terminal propeptide of procollagen type I (P1NP), serum ionized calcium (iCa), and plasma PTH were measured every 3 h over a 24 h period in 14 postmenopausal osteoporotic women (aged 72.4±9.3 years) treated with 20 µg TPTD for long term, given at different times of the day. General linear model-repeated measurements (GLM RM) were performed to analyze the circadian rhythms as well as intergroup comparisons. RESULTS: GLM-RM for both related groups showed a significant influence of time of day on all measured variables except P1NP. The analysis for each group separately provided a powerful model for ßCTX (P<0.001, η(2)=0.496), serum iCa (P<0.001, η(2)=0.423), plasma PTH (P<0.001, η(2)=0.283), and serum PINP (P<0.001, η(2)=0.248). While the evening TPTD treatment showed a marked circadian rhythm for serum ßCTX, the morning TPTD treatment rather suggested circasemidian rhythm. The P1NP rhythm followed a much smaller amplitude of the rhythm than ßCTX. Changes in serum iCa were positively related to changes in serum ßCTX (P<0.001) and negatively related to changes in PTH (P<0.001). CONCLUSION: Timing of TPTD administration may significantly change the 24 h variation in bone turnover markers as well as calcium-parathyroid axis in postmenopausal osteoporotic women.