Ten years of treatment with tibolone 2.5 mg daily: effects on bone loss in postmenopausal women

Hormone therapy in the postmenopausal years: considering benefits and risks in clinical practice

BACKGROUND

Menopausal symptoms can be very distressing and considerably affect a woman's personal and social life. It is becoming more and more evident that leaving bothersome symptoms untreated in midlife may lead to altered quality of life, reduced work productivity and, possibly, overall impaired health. Hormone therapy (HT) for the relief of menopausal symptoms has been the object of much controversy over the past two decades. At the beginning of the century, a shadow was cast on the use of HT owing to the concern for cardiovascular and cerebrovascular risks, and breast cancer, arising following publication of a large randomized placebo-controlled trial. Findings of a subanalysis of the trial data and extended follow-up studies, along with other more modern clinical trials and observational studies, have provided new evidence on the effects of HT.

OBJECTIVE AND RATIONALE

The goal of the following paper is to appraise the most significant clinical literature on the effects of hormones in postmenopausal women, and to report the benefits and risks of HT for the relief of menopausal symptoms.

SEARCH METHODS

A Pubmed search of clinical trials was performed using the following terms: estrogens, progestogens, bazedoxifene, tibolone, selective estrogen receptor modulators, tissue-selective estrogen complex, androgens, and menopause.

OUTCOMES

HT is an effective treatment for bothersome menopausal vasomotor symptoms, genitourinary syndrome, and prevention of osteoporotic fractures. Women should be made aware that there is a small increased risk of stroke that tends to persist over the years as well as breast cancer risk with long-term estrogen-progestin use. However, healthy women who begin HT soon after menopause will probably earn more benefit than harm from the treatment. HT can improve bothersome symptoms, all the while conferring offset benefits such as cardiovascular risk reduction, an increase in bone mineral density and a reduction in bone fracture risk. Moreover, a decrease in colorectal cancer risk is obtainable in women treated with estrogen-progestin therapy, and an overall but nonsignificant reduction in mortality has been observed in women treated with conjugated equine estrogens alone or combined with estrogen-progestin therapy. Where possible, transdermal routes of HT administration should be preferred as they have the least impact on coagulation. With combined treatment, natural progesterone should be favored as it is devoid of the antiapoptotic properties of other progestogens on breast cells. When beginning HT, low doses should be used and increased gradually until effective control of symptoms is achieved. Unless contraindications develop, patients may choose to continue HT as long as the benefits outweigh the risks. Regular reassessment of the woman's health status is mandatory. Women with premature menopause who begin HT before 50 years of age seem to have the most significant advantage in terms of longevity.

WIDER IMPLICATIONS

In women with bothersome menopausal symptoms, HT should be considered one of the mainstays of treatment. Clinical practitioners should tailor HT based on patient history, physical characteristics, and current health status so that benefits outweigh the risks.

A Review of Analytical Methods for the Determination of Tibolone: Pharmacokinetics and Pharmaceutical Formulations Analysis and Application in Doping Control

Background:

Tibolone is a synthetic steroid commercialized by Organon under the brand name Livial (Org OD14), which is used in hormone therapy for menopause management and treatment of postmenopausal osteoporosis. Tibolone is defined as a selective tissue estrogenic activity regulator (STEAR) demonstrating tissue-specific effects on several organs such as brain, breast, urogenital tract, endometrium, bone and cardiovascular system.

Aims:

This work aims to (1) present an overview of important published literature on existing methods for the analysis of tibolone and/or its metabolites in pharmaceutical formulations and biological fluids and (2) to conduct a critical comparison of the analytical methods used in doping control, pharmacokinetics and pharmaceutical formulations analysis of tibolone and its metabolites.

Results and conclusions:

The major analytical method described for the analysis of tibolone in pharmaceutical formulations is High Pressure Liquid Chromatography (HPLC) coupled with ultraviolet (UV) detection, while Liquid Chromatography (LC) or Gas Chromatography (GC) used in combination with Mass Spectrometry (MS) or tandem mass spectrometry (MS/MS) is employed for the analysis of tibolone and/or its metabolites in biological fluids.

Prevention of postmenopausal osteoporosis in Chinese women: a 5-year, double-blind, randomized, parallel placebo-controlled study

OBJECTIVES

To observe the effectiveness and safety of menopause-related hormone therapy (MHT) to prevent bone loss in Chinese women during the menopausal transition and early menopause, as well as to evaluate the effects of 5-year MHT on overall health to add Level I evidence for the prevention of osteoporosis using MHT.

DESIGN

This clinical study was a prospective, double-blind, randomized, parallel placebo-controlled study. Chinese women in the menopausal transition and early menopause were randomly allocated to the MHT group or the placebo group. All subjects received a 5-year intervention. The effectiveness of MHT for bone mineral density (BMD) and bone metabolism and the safety of MHT in relation to glycolipid metabolism, breast cancer, and cardiovascular disease were studied.

RESULTS

In the MHT group, women in both transition and early menopause showed a significant increase in lumbar and femoral neck BMD after the 1st year of therapy; BMD tended to decrease in the 3rd year but ultimately was sustained at stable levels that were near the baseline levels. In the placebo group, BMD decreased at both sites. Metabolism indexes and breast ultrasound examination findings did not differ significantly between the MHT and placebo groups. Three cases of breast cancer and three cases of cardiovascular disease were diagnosed during follow-up. One breast cancer case and two cardiovascular disease cases occurred in the MHT group.

CONCLUSIONS

Five-year sequential therapy with estrogen and progesterone can increase or maintain the BMD of women in their menopausal transition and early menopause. This regimen had no negative effect on glycolipid metabolism and did not increase the risk of breast cancer or cardiovascular events.

The effect of weight and weight change on the long-term precision of spine and hip DXA measurements

SUMMARY

We examined the effect of weight and weight change on the long-term precision of spine and hip bone mineral density (BMD) in a group of 64 postmenopausal women studied over a 10-year period. Long-term precision errors were 50% larger than short-term errors. Over the range 50-90-kg weight was associated with a statistically significantly larger precision error when precision was expressed in BMD units, but not when expressed as the coefficient of variation (CV). Weight changes up to 5 kg had little effect on precision.

INTRODUCTION

Reliable knowledge of the precision of bone mineral density (BMD) measurements is important for the interpretation of follow-up dual-energy X-ray absorptiometry (DXA) scans. In this study, we examined the effect of body weight and change in weight on the long-term precision of spine and hip BMD.

METHODS

The study population was a group of 64 postmenopausal women enrolled in a 16-year trial of tibolone. We analyzed the spine, femoral neck, and total hip BMD data acquired over a 10-year period on a Hologic QDR4500A densitometer using linear regression to examine the trend of BMD with time for each subject. Precision was expressed in BMD units (g cm(-2)) (standard error of the estimate, SEE) and also as the coefficient of variation (CV).

RESULTS

The long-term precision errors were in BMD (CV) units: 0.018 g cm(-2) (1.9%) for spine, 0.017 g cm(-2) (2.3%) for femoral neck, and 0.016 g cm(-2) (1.7%) for total hip BMD. An inverse relationship between CV and BMD was found for the spine (P = 0.003) and total hip (P = 0.043) sites, but none between SEE and BMD. For spine BMD, there were statistically significant correlations between SEE and weight (P = 0.025) and body thickness (P = 0.027). For femoral neck BMD, there were correlations between SEE and weight (P = 0.030), body mass index (BMI) (P = 0.023) and thickness (P = 0.021), but no correlations for total hip BMD or when precision was expressed as the CV. When study subjects were grouped in quartiles according to weight, the spine BMD SEE increased from 0.014 g cm(-2) for women in the lowest quartile (46-62 kg) to 0.018 g cm(-2) for women in the highest quartile (80-105 kg) (P = 0.008). There was a trend for SEE to be greater in individuals with larger weight changes, although these tended to be the heavier subjects.

CONCLUSIONS

From the study, we were able to come up with the following conclusions: (1) long-term precision errors were 50% larger than short-term errors, (2) over the range 50 to 90 kg (BMI: 20-35 kg m(-2)), body weight had a small but statistically significant effect on precision expressed in BMD units, but not when expressed as the CV, and (3) weight changes up to 5 kg had little effect on precision. More studies of individuals >100 kg are required to fully investigate the dependence of DXA scan precision on weight.

Tibolone in postmenopausal women: a review based on recent randomised controlled clinical trials

AIM

To critically discuss the use of tibolone (T), in light of a series of very recent double-blind placebo (PL) controlled trials (LISA, LIFT, OPAL, THEBES, LIBERATE) conducted worldwide in a large number of postmenopausal women (PMW).

METHODS

The most relevant publications on T therapy in PMW were considered with emphasis on menopausal symptoms, quality of life, sexuality, bone, cardiovascular system (CVS) and oncologic risk.

RESULTS

T significantly relieves climacteric symptoms and improves mood and sexual well-being (LISA). T is as effective as estrogen-progestin therapy in preventing bone loss and reducing the relative risk of vertebral and non-vertebral fractures (LIFT). By using surrogate endpoints of the individual risks for the CVS, studies show mixed results, but a favourable effect on acute miocardial infarction and thromboembolism has been documented (THEBES, LIFT, OPAL). Although findings about endometrial and colon cancer are reassuring, conclusive data on breast cancer risk with T are not available and an increased risk of recurrence in women with previous breast cancer emerged (LIBERATE).

CONCLUSIONS

T is effective in treating menopausal syndrome with a good tolerability profile. In spite of some unsolved issues in term of safety, T is still a good treatment option for early PMW.

Effects of tibolone and raloxifene on bone mineral density in osteopenic postmenopausal women

A randomized trial was conducted in osteopenic postmenopausal women to compare the efficacy of tibolone versus raloxifene on BMD of the lumbar spine and hip. Tibolone increased lumbar spine and total hip BMD to a statistically significantly greater extent than raloxifene after two years of treatment.

INTRODUCTION

Both tibolone, a selective tissue estrogenic activity regulator (STEAR), and raloxifene, a selective estrogen receptor modulator (SERM), are known to prevent postmenopausal bone loss. However, no head-to-head studies to compare the efficacy on bone have been performed.

METHODS

A double-blind, randomized trial was conducted in osteopenic postmenopausal women aged 60-79 years to compare the effects of tibolone 1.25 mg/day to raloxifene 60 mg/day on bone mineral density (BMD). Serum osteocalcin and serum type I collagen C-telopeptides were measured as biochemical markers of bone metabolism.

RESULTS

Three hundred and eight subjects were allocated to treatment. Both treatments significantly increased lumbar spine BMD, however the increase was significantly larger after tibolone treatment than after raloxifene treatment (at year 1: 2.2% versus 1.2%, p<0.01 and at year 2: 3.8% versus 2.1%, p<0.001). After 2 years of treatment, the increase in total hip BMD in the tibolone group was significantly larger than in the raloxifene group (p<0.05). Both treatments significantly reduced type I collagen C-telopeptides and osteocalcin levels when compared to baseline.

CONCLUSIONS

Tibolone 1.25 mg/day for 2 years prevents postmenopausal bone loss in older women and results in a larger increase of BMD both at the lumbar spine and hip than raloxifene.

Variations on hormone replacement therapy: an answer to the 'one dose fits all' Women's Health Initiative study

The Women's Health Initiative study worked on the assumption that one dose would fit all asymptomatic postmenopausal women. The investigators therefore often used the wrong dose, of the wrong hormones, on the wrong patients and therefore came to many wrong conclusions. Different combinations of different hormones are necessary for different symptoms and different age groups. Hormone replacement therapy may be commenced in the perimenopausal phase, the early postmenopause, the late postmenopause or after hysterectomy and bilateral salpingo-oophorectomy or a premature menopause. These all require different treatments. Similarly, various indications such as vasomotor symptoms, sexual problems, depression or the treatment/prevention of osteoporosis all need different combinations of estradiol and possibly progestogen and testosterone, according to the specific requirements of the patient.

Pharmacokinetic parameters of tibolone and metabolites in plasma, urine, feces, and bile from ovariectomized cynomolgus monkeys after a single dose or multiple doses of tibolone

Levels of nonsulfated and sulfated tibolone metabolites were determined in plasma, urine, and feces from six ovariectomized, mature female cynomolgus monkeys after a single dose and multiple p.o. doses (including bile) of tibolone using validated gas chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry assays. In plasma, the predominant nonsulfated metabolite after single and multiple dosing was the estrogenic 3alpha-hydroxytibolone; levels of the estrogenic 3beta-hydroxytibolone were 10-fold lower and of progestagenic/androgenic Delta(4)-tibolone, 5-fold lower. Tibolone was undetectable. The predominant sulfated metabolite was 3alphaS,17betaS-tibolone; levels of 3betaS,17betaS-tibolone were about 2-fold lower, and monosulfated 3-hydroxymetabolites were about 10-fold lower. After multiple doses, areas under the curve of nonsulfated metabolites were lower (2-fold), and those of sulfated metabolites were 25% higher. In plasma, >95% metabolites were disulfated. In urine, levels of all the metabolites after single and multiple doses were low. After a single dose, high levels of 3beta-hydroxytibolone and the 3-monosulfated metabolites (3betaS,17betaOH-tibolone and 3alphaS,17betaOH-tibolone) were found in feces. After multiple dosing, 3alpha-hydroxytibolone increased, and the ratio of 3alpha/3beta-hydroxytibolone became about 1. The predominant sulfated metabolite was 3alphaS,17betaS-tibolone. Levels of all the metabolites in feces were higher after multiple doses than after a single dose. Levels of nonsulfated and 3-monosulfated metabolites were higher in feces than in plasma. Bile contained very high metabolite levels, except monosulfates. This may contribute to the metabolite content of the feces after multiple doses. 3beta-Hydroxytibolone and 3alphaS,17betaS-tibolone predominated. In conclusion, tibolone had different metabolite patterns in plasma, urine, feces, and bile in monkeys. The bile contributed to the metabolite pattern in feces after multiple doses. The major excretion route was in feces.

Biological options to enhance periprosthetic bone mass

There is a potential for the use of pharmacological agents to enhance the quality of bone around a total hip or knee prosthesis, reducing the risk of implant failure or periprosthetic fracture. Bisphosphonates are currently used for the management of postmenopausal osteoporosis and recent investigations also suggest a potential role for the management of postoperative periprosthetic bone loss. Current evidence suggests that the short-term gains may not be sustained in the long term. Teriparatide and parathyroid hormone 1-84 have been licensed to treat postmenopausal osteoporosis and may also be investigated for the potential to enhance periprosthetic bone mass. In addition, other agents such as calcitonin and strontium ranelate, non-anabolic agents such as doxycycline, and recombinant OPG adeno-associated virus (rAAV) gene therapy, may in the future provide solutions for enhancing periprosthetic bone mass.

Pharmacokinetic Parameters of Sulfated Tibolone Metabolites in Postmenopausal Women after Single and Multiple Doses of Tibolone

The objective of this study was to determine pharmacokinetic parameters of sulfated tibolone metabolites after single dose and their accumulation after multiple doses of tibolone. Blood samples from postmenopausal women in a single-dose (2.5 mg tibolone), open-label study (n=8) and multiple-dose (placebo, 0.3, 0.625, 1.25, or 2.5 mg/day tibolone for twenty-six cycles of 28 days), randomized, double-blind study (n=15) were analyzed for non-sulfated and sulfated tibolone metabolites by validated gas chromatography-mass spectrometry (GC-MS) and liquid chromatography with tanolam mass spectrometry (LC-MS/MS), respectively. The predominant non-sulfated and sulfated metabolites after a single dose were 3alpha-hydroxy-tibolone and 3alpha,17beta-di-sulfated (di-S)-tibolone. At 3 h, >90% of metabolites were sulfated. Tibolone and Delta(4)-tibolone were detectable for about 6 h. After multiple treatment cycles with different doses, metabolite levels at 10 h were dose-related and levels of di-S metabolites were three- to fivefold higher than after a single dose. Tibolone metabolite levels did not differ between cycles. Inactive di-S tibolone metabolites predominated in blood. No accumulation occurred between cycles 7 and 26.

Serum leptin levels and body composition in postmenopausal women treated with tibolone and raloxifene

OBJECTIVE

To compare body composition and serum leptin levels in untreated postmenopausal women and postmenopausal women treated with tibolone or raloxifene.

DESIGN

This was a prospective, randomized, controlled study. Sixty-eight postmenopausal women were randomized to receive either no treatment (group A, n = 21) or tibolone 2.5 mg/day (group B; n = 23) or raloxifene 60 mg/day (group C; n = 24). All women underwent height, weight, body mass index evaluation and dual energy x-ray absorptiometry determination of body composition at the beginning of the study and after 12 months. Serum leptin levels were determined at the beginning of the study and after 1, 3, 6, and 12 months in all groups.

RESULTS

Women in group A showed no significant changes in both fat and lean mass of arms and legs, whereas a significant increase in trunk fat mass, total fat mass, total percentage of body fat, and trunk percentage of fat was detected 1 year after the beginning of the study. After 12 months, the total percentage of fat mass was significantly higher in group A compared with group B, and the trunk percentage of fat mass was significantly higher in group A compared with groups. In subjects in groups B and C, after 1 year, fat mass, both total and at all areas evaluated, did not show any significant change compared with baseline values. In subjects in group B, total lean and lean mass of the trunk and legs increased significantly at the end of the study, whereas no significant changes were observed in lean mass, total and at all areas evaluated in subjects in group C. After 12 months, total lean mass and lean mass of the legs were significantly higher in group B compared with the other groups. In group A, serum leptin levels were significantly increased at the end of the study compared with baseline values. Leptin concentrations were significantly higher in group A compared with groups B and C after 6 and 12 months. No significant change in serum leptin levels in subjects in groups B and C was detected throughout the study. Serum leptin levels showed a positive, significant correlation with all body composition parameters and body mass index in all groups at the beginning and at the end of the study.

CONCLUSIONS

The present study confirms that postmenopausal hypoestrogenism leads to increased fat content and serum leptin levels. Raloxifene and tibolone seem to prevent postmenopausal body composition changes without significant modifications of serum leptin levels.

Effects of stable transfection of human fetal osteoblast cells with estrogen receptor-alpha on regulation of gene expression by tibolone

Tibolone is a synthetic steroid which undergoes tissue selective metabolism into several metabolites having estrogenic, progestogenic or androgenic activities. The effects of 3 alpha-hydroxy tibolone (Org 4094), 3 beta-hydroxy tibolone (Org 30126) and their sulfated metabolites were investigated on human fetal osteoblasts (hFOB). Tibolone had no effect on selected osteoblast marker proteins in estrogen-receptor negative hFOB cells. In contrast, 3 alpha-hydroxy and 3beta-hydroxy tibolone resulted in dose-dependent increases in alkaline phosphatase activity in estrogen receptor (ER) alpha-positive hFOB cells. The maximum increase for both metabolites was comparable to the effects of an optimal dose of 17beta-estradiol, and occurred at 10 muM. At 20 muM, both metabolites increased mRNA levels for alkaline phosphatase and type 1 collagen and protein levels for osteocalcin. Sulfated metabolites of tibolone also increased alkaline phosphatase activity. The estrogen receptor antagonist ICI 182, 780 inhibited stimulation of alkaline phosphatase activity by sulfated and non-sulfated tibolone metabolites, but was more potent on the former. Taken together, these results suggest that stable transfection of ER alpha into hFOB cells confers regulation by 3 alpha-hydroxy and 3beta-hydroxy tibolone metabolites of osteoblast metabolism.

Effects of tibolone on body composition in postmenopausal women: a 1-year follow up study

OBJECTIVE

We investigated the effects of 1-year tibolone treatment on body weight, body composition and indices of android obesity in postmenopausal women.

METHODS

Forty-four postmenopausal women participated in this open-label controlled study; mean age was 51.8+/-2.21 years and all women were menopausal for 3.8+/-1.40 years. Twenty-two of them started taking 2.5 mg tibolone (TIB) daily for 1 year, whereas the remaining 22 served as age-matched controls. All subjects underwent a structured interview, physical examination, body composition measurements performed by dual-energy X-ray absorptiometry (DXA) - Hologic QDR 4500 A, as well as bioelectrical body impedance analysis (BI) - Tanita TBF-215, Japan.

RESULTS

The TIB group did not significantly increase their weight (+0.4 kg), while the non-treated controls increased their mean weight by 1.4 kg (p=0.046). In the TIB group, DXA showed a non-significant body fat decrease by a mean of 0.5 kg and a non-significant lean mass increase by 0.8 kg, while in the control group, fat mass increased by 1.7 kg (p=0.032) and lean mass did not change. BI revealed that the TIB group had lost some fat ( approximately 0.6 kg, n.s.) and put some free-fat mass ( approximately 1.0 kg, p=0.048) without changes in total body water. The control group put on some fat ( approximately 1.1 kg, p=0.042) and lost some body water ( approximately 0.4 kg, n.s.).

CONCLUSION

Results from both methods of measuring body composition show a similar trend: a decrease in fat mass and an increase in lean mass in TIB treated subjects. From the body composition perspective, tibolone may be regarded as a preferential alternative to conventional hormonal therapy (HT) in postmenopausal women.

Effect of misoprostol on bone mineral density in women with postmenopausal osteoporosis

OBJECTIVE

To evaluate the effect of misoprostol on bone mineral density in postmenopausal women.

MATERIALS AND METHODS

The study was performed in a randomized controlled prospective manner in 90 women with menopause at Süleymaniye Maternity and Women's Diseases Teaching and Research Hospital between January and December 2003. Cases were divided into three groups each consisting of 30 women who were in menopause for at least 1 year and had t-scores less than -1 by dual energy X-ray densitometry (DEXA). Group I was treated with misoprostol and calcium, Group II received tibolone and calcium and Group III was given calcium only and considered as control group. In all patients, bone mineral density in L1-L4 vertebrae, femur neck and Ward triangle were measured by DEXA and t and z scores were calculated.

RESULTS

All groups were similar demographically. Bone mineral density in L1-L4 vertebrae, femur neck and Ward triangle in the group treated with misoprostol, increased by 5, 8.1 and 3.6%, respectively. In the tibolone group, bone mineral density in L1-L4 vertebrae, femur neck and Ward triangle increased by 8.3, 5.3 and 7.8%, respectively. There was not a significant difference in t and z-scores and bone mineral density measurements between misoprostol and tibolon groups.

CONCLUSION

Misoprostol may be an alternative treatment for patients with osteopenia and osteoporosis who are not suitable for hormone replacement therapy.

Interrelationships of serum estradiol, estrone, and estrone sulfate, adiposity, biochemical bone markers, and leptin in post-menopausal women

OBJECTIVE

The aim of this study was to examine the relationships between endogenous estrogens and adiposity, bone markers, and leptin in post-menopausal (PM) women.

DESIGN

Seventy-three post-menopausal (PM) women participated in a clinical correlational study. Weight, height, waist-hip ratio, fasted morning serum and first morning voided urine samples were obtained to compare body mass index (BMI), waist-hip ratio, endogenous estrogens, leptin, and bone markers. Serum estradiol, estrone (E1), estrone sulfate (E1S), leptin, osteocalcin, and urinary deoxypyridinoline (Dpd) were determined.

RESULTS

Significant positive relationships were found between BMI and estradiol, E1, and E1S (r = 0.52, 0.38, and 0.29; P < or = 0.001, 0.001, and 0.013 respectively). Significant relationships between leptin and estrogens were revealed, but were not significant when BMI was used as a covariate. Although many subjects revealed elevated bone marker levels, no correlation between estrogens or BMI and bone markers (Dpd and osteocalcin) was found.

CONCLUSIONS

There are significant positive correlations between estrogens and BMI in PM women. Increasing levels of estradiol, E1, and E1S with increasing BMI may be an indicator of adiposity, but are without effect as a stimulatory factor on leptin production. Waist-hip ratio did not significantly affect leptin concentrations when accounting for BMI. Due to assay sensitivity in the present study, data represent a more precise representation of these relationships. The lack of correlation between estrogens and bone marker levels may have been due to low estrogen levels in PM women.

Tibolone: Clinical recommendations and practical guidelines

An international multidisciplinary panel of experts in the management of the menopause met at the 4th Amsterdam Menopause Symposium in October 2004 to determine the specific place of tibolone, a synthetic steroid with a unique clinical profile, within the wide range of currently available postmenopausal therapy options. The consensus was that tibolone is a valuable treatment option for women with climacteric complaints. As well as relieving vasomotor symptoms, tibolone has positive effects on sexual well-being and mood, and improves vaginal atrophy and urogenital symptoms. Prevention of bone loss with tibolone is comparable to that seen with estrogen therapy (ET) and estrogen/progestogen therapy (EPT). As tibolone rarely causes endometrial proliferation, no additional progestogen is required. It also has good tolerability, being associated with a low incidence of vaginal bleeding and of breast pain. Tibolone does not increase mammographic density. Absolute numbers of women at increased risk for breast cancer are estimated to be low or absent with both tibolone and ET, and the risk with tibolone should be significantly lower than that with EPT. Tibolone might therefore be preferable to EPT in certain women who have not been hysterectomised. Based on the evidence available, the panel proposed a number of subgroups of postmenopausal women with vasomotor symptoms in whom tibolone might have added value; these included women with sexual dysfunction, mood disorders, fibroids and urogenital complaints, as well as those with breast tenderness or high mammographic breast density with EPT use.

Pros and cons of existing treatment modalities in osteoporosis: a comparison between tibolone, SERMs and estrogen (+/-progestogen) treatments

Tibolone, selective estrogen receptor modulators (SERMs) like tamoxifen and raloxifene, and estrogen (+/-progestogen) treatments prevent bone loss in postmenopausal women. They exert their effects on bone via the estrogen receptor (ER) and the increase in bone mass is due to resorption inhibition. The effect of SERMs on bone mineral density is less than that with the other treatments, but the SERM raloxifene still has a positive effect on vertebral fractures. In contrast to tibolone and estrogens (+/-progestogen), SERMs do not treat climacteric complaints, whilst estrogen plus progestogen treatments cause a high incidence of bleeding. Estrogen plus progestogen combinations have compromising effects on the breast. Tibolone and SERMs do not stimulate the breast or endometrium. Unlike SERMs, tibolone does not possess antagonistic biological effects via the ER in these tissues. Estrogenic stimulation in these tissues is prevented by local metabolism and inhibition of steroid metabolizing enzymes by tibolone and its metabolites. SERMs and estrogen (+/-progestogen) treatments increase the risk of venous thromboembolism (VTE), whilst estrogen (+/-progestogen) combinations have unwanted effects on cardiovascular events. So far, no detrimental effects of tibolone have been observed with respect to VTE or cardiovascular events. The clinical profile of tibolone therefore has advantages over those of other treatment modalities. It is also clear that tibolone is a unique compound with a specific mode of action and that it belongs to a separate class of compounds that can best be described as selective, tissue estrogenic activity regulators (STEARs).