Variability in the measured response of bone to teriparatide

Summary Apparent failures of bone mineral density (BMD) response to teriparatide at spine or hip occur even in a high compliance context (15% spine and 55% hip). Apparent non-responders nevertheless show good biomarker response, suggesting that apparent BMD non-response is due to measurement imprecision. Calcium intake may be an important determinant of hip response. Introduction Individuals vary in response to bone active agents, but that variability is poorly quantified and its basis is not well understood. The study included 203 postmenopausal women with moderately severe osteoporosis, all treated with teriparatide, calcium, and vitamin D. The study was performed at the Creighton University Medical Center, a single site. Methods This is a prospective study of change in bone mineral density and resorption biomarkers over a 12-month treatment period. BMD response at spine and total hip was quantified by computing slopes for each participant’s values, and biomarker change by the difference in values across the 12-month study period. Results Of the total number of participants, 85.2% exhibited a significant spine BMD response, while only 44.8% had a significant change at the hip. However, mean biomarker response was marginally larger for the BMD non-responders at either site than for the responders, indicating biological, if not measurable densitometric, activity of teriparatide in essentially all participants. Conclusions Occasional apparent failures of BMD response in patients receiving teriparatide are probably not due to failure of response at the level of the bone remodeling apparatus, but instead reflect a combination of measurement imprecision and variable bone remodeling balance. The reason for the latter remains unclear.