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 (βCTX), 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 βCTX (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 βCTX, the morning TPTD treatment rather suggested circasemidian rhythm. The P1NP rhythm followed a much smaller amplitude of the rhythm than βCTX. Changes in serum iCa were positively related to changes in serum βCTX (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.

Department of Internal Medicine 3 Department of Endocrinology and Metabolism 1st Faculty of Medicine Charles University Prague and General University Hospital Prague U Nemocnice 1 Cz 128 08 Prague Czech Republic

Institute of Information Theory and Automation Czech Academy of Sciences Cz 182 08 Prague Czech Republic

Institute of Rheumatology Charles University Faculty of Medicine 1 Cz 128 08 Prague Czech Republic

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