This time difference in the responses of bone turnover markers in daily teriparatide

injection has been referred to as an “anabolic window” [9]. The anabolic window was presented as the reason that daily teriparatide injection increased BMD. However, the late-phase increase in bone resorption markers may rapidly decrease BMD after teriparatide injections are stopped [13]. Although the daily administration of teriparatide showed clinical benefits including fracture prevention [2] and improvement of patients’ Opaganib datasheet quality of life [14], the daily self-administered regimen is bothersome, especially for elderly patients. Fujita et al. reported that once-weekly administration of teriparatide effectively increased BMD in postmenopausal osteoporosis patients [11], and Nakamura et al. reported a significant risk reduction for fracture [4]. However, there had been no available data to demonstrate why once-weekly administration of teriparatide effectively increases BMD. PK analysis in the present study revealed that the teriparatide concentration peaked after 1 h and disappeared 6 h after a single injection. To respond to the rapid rise in teriparatide, serum calcium and urinary phosphate excretion transiently increased. Increases in the serum level of 1,25(OH)2D in response CHIR-99021 research buy to teriparatide injection were observed. These changes in calcium metabolism were within

our expectation, and the findings indicated that a single injection of teriparatide is biologically active in terms of calcium metabolism. Cosman et al. reported that daily 20 μg teriparatide injections increased 1,25(OH)2D levels with a peak effect occurring at 1 month and a persistent increase over 1 year [15]; a similar result was seen with weekly 56.5 μg teriparatide therapy [11]. The response of bone turnover markers to a single administration of teriparatide had not previously been investigated. The present study indicated that a single administration of teriparatide caused biphasic changes in bone formation and resorption markers, namely, a rapid increase in resorption markers

and decrease in formation markers for 1 or 2 days, followed by a sustained suppression of resorption markers and Quisqualic acid stimulation of formation markers for the subsequent 2 to 14 days. These bone marker changes did not show dose dependency except for serum NTX, and the magnitude of change in bone markers was smaller than the changes seen with daily administration of teriparatide [16]. The sustained late-phase response of bone turnover markers in the present study may be one possible explanation for the BMD increase seen with weekly administration of teriparatide. The present study includes several limitations. First, most of the changes in calcium metabolic and bone turnover markers after a single administration of teriparatide did not show dose-related differences.