Context: We have previously demonstrated that alendronate reduces the ability of teriparatide to increase bone mineral density (BMD) in osteoporotic men. The underlying basis for this observation is poorly understood.
Objective: The primary aim of this study was to determine whether teriparatide increases osteoblast activity when the ability of teriparatide to increase osteoclast activity is suppressed by alendronate.
Design: This was a nonblinded, randomized, controlled trial.
Setting: The study was conducted at the General Clinical Research Center of a teaching hospital.
Patients: We studied 63 men, age 46-85, with low spine and/or hip BMD.
Interventions: Subjects received alendronate 10 mg daily (group 1), teriparatide 37 microg sc daily (group 2), or both (group 3) for 30 months. Teriparatide was begun at month 6.
Main outcome measures: The primary endpoint was the change in serum N-telopeptide, osteocalcin, and amino-terminal propeptide of type 1 procollagen.
Results: In men receiving teriparatide monotherapy (group 2), levels of all bone turnover markers increased markedly during the first 6 months of teriparatide administration and then declined toward baseline during the next 18 months. In men who received combination therapy (group 3), bone turnover marker levels declined in the first 6 months (while receiving alendronate alone) and then returned to baseline levels (N-telopeptide) or above (osteocalcin and amino-terminal propeptide of type 1 procollagen) after teriparatide was added. Changes in each marker were significantly different between groups 1 and 2 (all P values < 0.001), groups 1 and 3 (all P values < 0.001), and groups 2 and 3 (all P values < 0.03).
Conclusions: As with BMD, alendronate impairs the action of teriparatide to increase bone turnover in men.