Alendronate reduced ability of teriparatide to increase BMI, bone turnover in women

Adding alendronate impaired the ability of teriparatide to increase bone mineral density and bone turnover in postmenopausal women, according to new data.

The study evaluated the effects of combining teriparatide, which is generally given for two years, with alendronate in women with postmenopausal osteoporosis. Researchers randomly assigned 93 postmenopausal women with low BMD to 30-month treatment with alendronate 10 mg daily (Fosamax, Merck), teriparatide 40 mcg daily (Forteo, Eli Lilly) or a combination of both. Teriparatide was initiated at six months. DEXA was performed every six months, and women were administered baseline and 30-month quantitative CT assessments.

Women who received teriparatide alone experienced increased spine BMD compared with women who received alendronate alone (17.8% vs. 6.8%; P<.001) or both (17.8% vs. 11.9%; P=.045). Similarly, women who received teriparatide alone experienced increased femoral neck BMD compared with those administered alendronate alone (10.8% vs. 3.5%, P<.001) or both (10.8% vs. 3.1%, P<.001).

Spine BMD, as measured by quantitative CT, was increased in all three groups: by 61% with teriparatide; 1% with alendronate; and 24% with combination therapy (P<.001 for all).

In addition, women assigned teriparatide alone experienced greater increases in serum osteocalcin, N-terminal propeptide of type 1 collagen and cross-linked N-telopeptides of type 1 collagen compared with women assigned alendronate alone or combination therapy.

Further research was recommended to determine whether other antiresorptive agents have a similar BMD/bone formation effect when used in conjunction with teriparatide.

“Although the effects on fracture risk of these complex interactions are unknown, these findings may help inform clinicians considering treatment of postmenopausal osteoporotic women with teriparatide, particularly if a full two-year course of therapy is planned,” the researchers wrote.

Of note, these data are “virtually identical” to those previously reported in men who underwent an identical protocol, according to the researchers.

Finkelstein JS. J Clin Endocrinol Metab. 2010;95:1838–1845.