Effects of tibolone on serum lipoprotein and apolipoprotein levels compared with a cyclical estrogen/progestogen regimen.

Objective: The purpose of the study was to examine the effects of tibolone, a synthetic steroid that alleviates climacteric symptoms and prevents bone loss without inducing monthly bleeds, on lipoprotein cardiovascular risk markers and to compare the effects with those of a standard combined estrogen/progestogen preparation.

Design: Ninety-seven postmenopausal women were randomly allocated to receive either tibolone 2.5 mg/day or conjugated equine estrogens 0.625 mg/day with norgestrel 0.15 mg/day for 12 of each 28 days. Fasting serum levels of lipids, lipoproteins, and apolipoproteins (Apo) were monitored during 18 months of treatment. Women on the cyclical preparation had levels determined during both estrogen-only and combined phases.

Results: Tibolone caused reductions in triglycerides (33%, p < 0.001), very low density lipoprotein (VLDL) cholesterol (43%, p < 0.001), and high density lipoprotein (HDL) cholesterol (18%, p < 0.001). The HDL2/HDL3 ratio fell by 22% (p < 0.001). Levels of Apo AI and AII were reduced by 18 and 8%, respectively (p < 0.001). The combined preparation caused reductions in VLDL cholesterol (23%, p < 0.001) and low density lipoprotein cholesterol (15%, p < 0.001). There were small reductions in HDL3 cholesterol and in Apo AII and Apo B. All parameters, except for Apo AII and Apo B and lipoprotein (a) [Lp (a)], showed cyclical changes. Lp (a) levels were reduced significantly by both treatments.

Conclusions: The cyclical preparation had potentially beneficial effects on LP risk markers. The reduction in HDL induced by tibolone constitutes a potentially adverse change, which may be offset by the substantial falls in triglycerides, VLDL cholesterol, and Lp (a).