Context: The stimulatory effect of teriparatide on bone mineral density (BMD) and bone turnover is initially exuberant, but then diminishes.
Objective: Our objective was to determine whether retreating with teriparatide after a drug-free period can restore the initial exuberant response to teriparatide.
Design and setting: This was a planned extension of a randomized controlled trial conducted in a single university hospital.
Patients and intervention: Subjects previously participated in a 30-month randomized trial comparing the effects of alendronate (group 1), teriparatide (group 2), or both (group 3) on BMD and bone turnover in men and women with low BMD (phase 1). Subjects who completed phase 1 on their assigned therapy entered phase 2 (months 30-42), during which teriparatide was stopped in groups 2 and 3. Teriparatide was administered to all subjects during months 42 to 54 (phase 3).
Main outcome measures: We compared changes in BMD and markers of bone turnover (serum osteocalcin, N-terminal propeptide of type 1 collagen, and N-telopeptide) between phase 1 and 3 in subjects receiving teriparatide alone.
Results: Posterior-anterior and lateral spine BMD increased 12.5 +/- 1.5 and 16.9 +/- 1.7%, respectively, during the first 12 months of teriparatide administration and 5.2 +/- 0.8 and 6.2 +/- 1.8%, respectively, during teriparatide retreatment (P < 0.001 and P = 0.001). Increases in osteocalcin (P < 0.001), N-terminal propeptide of type 1 collagen (P < 0.001), and N-telopeptide (P < 0.001) were greater during the first period of teriparatide administration.
Conclusion: The response to teriparatide is attenuated when readministered after a 12-month hiatus.
Trial registration: ClinicalTrials.gov NCT00000400.