Efficacy and safety of estradiol transdermal system (twice-weekly) in the prevention of postmenopausal osteoporosis have been studied in a 2-year, double-blind, randomized, placebo-controlled, parallel group study. A total of 261 hysterectomized (161) and non-hysterectomized (100), surgically or naturally menopausal women (within 5 years of menopause), with no evidence of osteoporosis (lumbar spine bone mineral density within 2 standard deviations of average peak bone mass, i.e., at least 0.827 g/cm2) were enrolled in this study; 194 women were randomized to 1 of the 4 doses of estradiol transdermal system (twice-weekly) (0.1, 0.05, 0.0375, or 0.025 mg/day) and 67 patients to placebo. Over 2 years, study systems were applied to the buttock or the abdomen twice a week. Non-hysterectomized women received oral medroxyprogesterone acetate (2.5 mg/day) throughout the study.

The study population comprised naturally (82%) or surgically (18%) menopausal, hysterectomized (61%) or non-hysterectomized (39%) women with a mean age of 52 years (range 27 to 62 years); the mean duration of menopause was 31.7 months (range 2 to 72 months). Two hundred thirty-two (89%) of randomized women (173 on active drug, 59 on placebo) contributed data to the analysis of percent change from baseline in bone mineral density (BMD) of the AP lumbar spine, the primary efficacy variable. Women were given supplemental dietary calcium (1000 mg elemental calcium/day) but no supplemental vitamin D. There was an increase in BMD of the AP lumbar spine in all estradiol transdermal system (twice-weekly) dose groups; in contrast to this, a decrease in AP lumbar spine BMD was observed in placebo patients. All estradiol transdermal system (twice-weekly) doses were significantly superior to placebo (p<0.05) at all time points with the exception of estradiol transdermal system (twice-weekly) 0.05 mg/day at 6 months. The highest dose of estradiol transdermal system (twice-weekly) was superior to the 3 lower doses. There were no statistically significant differences in pairwise comparisons among the 3 lower doses (See Figure 3).

Figure 3. Bone Mineral Density-AP Lumbar Spine Least Squares Means of Percentage Change from Baseline All Randomized Patients with at Least One Post-baseline Assessment Available with Last Post-baseline Observation Carried Forward

Analysis of percent change from baseline in femoral neck BMD, a secondary efficacy outcome variable, showed qualitatively similar results; all doses of estradiol transdermal system (twice-weekly) were significantly superior to placebo (p<0.05) at 24 months. The highest estradiol transdermal system (twice-weekly) dose was superior to placebo at all-time points. A mixture of significant and nonsignificant results were obtained for the lower dose groups at earlier time points. The highest estradiol transdermal system (twice-weekly) dose was superior to the 3 lower doses, and there were no significant differences among the 3 lower doses at this skeletal site (See Figure 4).

Figure 4. Bone Mineral Density-Femoral Neck Least Squares Means of Percentage Change from Baseline All Randomized Patients with at Least One Post-baseline Assessment Available with Last Post-baseline Observation Carried Forward

The mean serum osteocalcin (a marker of bone formation) and urinary excretion of cross-link N-telopeptides of Type 1 collagen (a marker of bone resorption) decreased numerically in most of the active treatment groups relative to baseline. However, the decreases in both markers were inconsistent across treatment groups and the differences between active treatment groups and placebo were not statistically significant.