An 18-month randomized double-blind study was conducted in postmenopausal women 
with osteoporosis to compare the effects of once-daily teriparatide 20 microg 
with alendronate 10 mg on bone histomorphometry. Biopsies were obtained from 42 
patients. Indices of bone formation were significantly higher after 6 or 18 
months of teriparatide compared with alendronate treatment.
INTRODUCTION: Alendronate and teriparatide increased BMD, assessed by DXA, by 
different mechanisms of action, supported by changes in biochemical markers of 
bone turnover. The purpose of this cross-sectional study was to explore the 
differential effects of these two osteoporosis treatments at the bone tissue 
level by examining bone histomorphometric parameters of bone turnover after 
either 6 or 18 months of treatment.
MATERIALS AND METHODS: Patients were a cohort from a randomized parallel 
double-blind study conducted to compare the effects of once-daily teriparatide 
20 microg and alendronate 10 mg in postmenopausal women with osteoporosis. 
Transiliac crest bone biopsies were obtained after tetracycline double labeling 
from 42 patients treated for 6 months (n = 23) or 18 months (n = 14); 5 
additional patients were biopsied from contralateral sides at 6 and 18 months. 
Biopsy specimens adequate for quantitative analysis were analyzed by 2D 
histomorphometry from 17 patients at 6 months (teriparatide, n = 8; alendronate, 
n = 9) and 15 patients at 18 months (teriparatide, n = 8; alendronate, n = 7). 
Data were analyzed by two-sample tests.
RESULTS: Histomorphometric indices of bone formation were significantly and 
markedly greater in the teriparatide group than in the alendronate group at 6 
and 18 months, whereas indices of bone resorption were only significantly 
greater in the teriparatide group than in the alendronate group at 6 months. 
Bone formation and activation frequency were significantly lower at 18 months 
compared with 6 months in the teriparatide group, returning to levels comparable 
with untreated postmenopausal women. In the teriparatide group, the peak in 
histomorphometric bone formation indices coincided with peak levels for 
N-terminal propeptide of type I collagen, a biochemical marker of bone 
formation. The degree of mineralization was lower at 18 months than at 6 months 
with treatment in both groups but was not different between groups.
CONCLUSIONS: These results confirm the opposite mechanisms of action of 
teriparatide and alendronate on bone remodeling and confirm the bone formation 
effect of teriparatide.