Effect of dosing frequency of teriparatide (PTH 1-34) on bone formation in rats: comparison of bone metabolism marker levels.

Teriparatide, a drug used in the treatment of osteoporosis, was administered to rats subcutaneously for the duration of 3 months, at a frequency of either once weekly or once daily to demonstrate the varying levels of anabolic action the drug can have on bone depending on the dosing frequency. The levels of biomarkers in the blood were compared and found to vary in osteocalcin (OC), a biomarker of bone formation, and cross-linked N-telopeptide of type 1 collagen (NTx), a biomarker of bone resorption, according to the dosing frequency. In the once-weekly regimen, teriparatide did not affect NTx levels at any of the doses studied, while OC levels increased with dose, peaking at 72 hr, then returning to normal before the next injection (after 1 week). Bone mineral density (BMD) levels increased moderately with no difference between doses. This was thought to result from the steady state achieved following increases in bone formation and bone absorption. In the once-daily dosing regimen, meanwhile, NTx levels increased with dose, and OC levels were markedly higher when compared to those with the once-weekly dosing. BMD levels were higher than those with the once-weekly dosing, but with no difference between doses. This was considered a result of unlimited, excessive increases in bone formation due to daily administration of the drug. These results suggest that teriparatide promotes normal bone metabolism ("stationary mini-modeling") when administered once weekly, and has an anabolic action with high metabolic turnover ("high-turnover remodeling") when administered once daily.