Purpose: To evaluate the effects of cyclic vs daily teriparatide treatment (TPTD) on volumetric bone mineral density (vBMD) and bone strength at the hip and spine in women who were previously untreated.
Methods: A total of 86 women were randomized to a 24-month open label treatment of either daily TPTD (20 μg daily) or cyclic TPTD (20 μg daily for 3 months followed by 3 months off). During a 2-year extension, women in the daily TPTD group were switched to alendronate (ALN) and those in the cyclic TPTD group continued on cyclic TPTD (without any ALN). QCT images were acquired at baseline, 2-years (n = 54) and 4-years (n = 35) and analyzed for volumetric integral, cortical and trabecular bone mineral density (vBMD) and bone strength (by finite element analysis) at the hip and spine. The primary analysis presented here compared the responses across equal total TPTD doses (2 years daily vs 4 years cyclic).
Results: In the spine, integral vBMD and strength increased substantially after 2 years daily and 4 years cyclic TPTD, with no significant differences (vBMD +12 % vs +11 %, respectively, p = 0.70; spine strength +21 % vs +16 %, respectively, p = 0.35). At the hip, the gains were smaller, but again no significant differences were detected between the groups for the increases in either vBMD (+2 % in both groups, p = 0.97) or hip strength (3 % vs 3 %, p = 0.91). In the spine, the vBMD increment was about twice as large in the trabecular vs peripheral compartment; in the hip, significant vBMD gain was seen only in the trabecular compartment.
Conclusions: The gains in volumetric BMD and bone strength for an equivalent dose of TPTD did not depend on whether it was administered every day over two years or cyclically over four years.