Abstract
Tibolone, a novel compound with tissue-specific effects, has been found to have antiresorptive properties in bone. To confirm the efficacy of tibolone and determine its minimum effective dose for prevention of bone loss in early postmenopausal women, two randomized, double-blind, placebo-controlled, dose-finding studies were performed. Seven hundred seventy healthy women postmenopausal within 1-4 yr, with normal bone density for their age, were treated for 2 yr with 0.3, 0.625, 1.25, or 2.5 mg tibolone daily or placebo. All subjects took supplemental calcium carbonate (500 mg daily). Bone mineral density (BMD) of the lumbar spine and right proximal femur was measured by dual-energy x-ray absorptiometry for up to 2 yr. At each dose level, except the lowest (0.3 mg), tibolone produced a progressive increase in lumbar spine and total hip BMD over the 2-yr treatment period; at 0.3 mg, total hip density was maintained. However, only the doses 1.25 mg and 2.5 mg produced a progressive increase in femoral neck BMD. The differences in mean percent change from baseline in spine and total hip density were significant (P <0.05) for all tibolone dose groups compared with placebo at all time points. Tibolone was well tolerated, with a similar overall incidence of adverse events compared with placebo. Tibolone 1.25 mg per day is recommended because it shows a positive and statistically significant change in BMD of spine and femoral neck.