Tibolone: how does its mechanism of action translate into clinical effects

Oral Therapeutics Post Menopausal Osteoporosis

Osteoporosis affects a significant number of postmenopausal women in the United States. Screening is performed using clinical assessments and bone mineral density scans via dual x-ray absorptiometry. Oral therapy is indicated to prevent pathologic fractures in those deemed at increased risk following screening. Bisphosphonates including alendronate, ibandronate, and risedronate are currently first-line oral therapeutics in fracture prevention following the diagnosis of osteoporosis. Hormonal therapies include estrogen-containing therapies, selective estrogen receptor modulators, and other compounds that mimic the effects of estrogen such as tibolone. Lifestyle modifications such as supplementation and physical activity may also contribute to the prevention of osteoporosis and are used as adjuncts to therapy following diagnosis. These therapeutics are limited primarily by their adverse effects. Treatment regimens should be tailored based on significant risk factors demonstrated by patients, adverse effects, and clinical response to treatment. The most severe risk factors relevant to pharmacological selection involve hormone replacement therapies, where concern for venous thrombosis, coronary artery disease, breast, and uterine cancer exist. Bisphosphonates are most commonly associated with gastrointestinal discomfort which may be mitigated with proper administration. Although adverse effects exist, these medications have proven to be efficacious in the prevention of vertebral and non-vertebral fractures in post-menopausal women. Fracture risk should be weighed against the risk of adverse events associated with each of the regimens, with clinical judgment dictating the treatment approach centered around patient goals and experiences.

Effects of tibolone or continuous combined oestradiol/norethisterone acetate on glucose and insulin metabolism

OBJECTIVE

To determine the effects of tibolone or oestradiol (E(2) )/norethisterone acetate (NETA) hormone replacement therapy on glucose and insulin metabolism in postmenopausal women.

DESIGN

Single-centre double-blind placebo-controlled randomized clinical trial.

SUBJECTS/METHODS

We randomized 105 healthy postmenopausal women to tibolone 2·5 mg daily, continuous combined oral E(2) 2 mg/NETA 1 mg daily or placebo over a 2-year study. We performed intravenous glucose tolerance tests (IVGTT) with measurements of plasma glucose, insulin and C-peptide concentrations and the IVGTT glucose elimination rate, k. Mathematical modelling was performed to determine measures of insulin sensitivity, S(i) , pancreatic insulin secretion and hepatic and plasma insulin elimination.

RESULTS

Tibolone decreased S(i) to 53-63% and k to 72-79% of baseline values but increased IVGTT phase 2 C-peptide concentrations 1·6-1·8-fold and pancreatic insulin secretion 2·2-2·4-fold, so overall IVGTT glucose concentrations were unaffected. Similar, but for k, significantly smaller changes in insulin and C-peptide secretion were seen with E(2) /NETA, also with no effect on overall IVGTT glucose concentrations.

CONCLUSIONS

Tibolone reduces insulin sensitivity. Healthy postmenopausal women seem able to compensate for this and maintain normal postload glucose concentrations, but it may not be advisable to prescribe tibolone to women with, or at increased risk for, diabetes.

Influence of estrogen deficiency and tibolone therapy on trabecular and cortical bone evaluated by computed radiography system in rats

PURPOSE: To verify the effects of tibolone administration on trabecular and cortical bone of ovariectomized female rats by computed radiography system (CRS). METHODS: The experiment was performed on two groups of rats previously ovariectomized, one received tibolone (OVX+T) while the other did not (OVX), those groups were compared to a control group (C) not ovariectomized. Tibolone administration (1mg/day) began thirty days after the ovariectomy and the treatment remained for five months. At last, the animals were euthanized and femurs and tibias collected. Computed radiographies of the bones were obtained and the digital images were used to determine the bone optical density and cortical thickness on every group. All results were statistically evaluated with significance set at P<0.05%. RESULTS: Tibolone administration was shown to be beneficial only in the densitometric analysis of the femoral head, performing higher optical density compared to OVX. No difference was found in cortical bone thickness. CONCLUSION: Ovariectomy caused bone loss in the analyzed regions and tibolone administered in high doses over a long period showed not to be fully beneficial, but preserved bone mass in the femoral head.

Updated clinical recommendations for the use of tibolone in Asian women

Tibolone, which is indicated for the relief of climacteric symptoms and the prevention of osteoporosis in postmenopausal women, has a tissue-specific mode of action different to that of conventional hormone replacement therapy (HRT). A large proportion of Asian postmenopausal women experience symptoms that most frequently include musculoskeletal pain, insomnia, forgetfulness, hot flushes and sexual dysfunction, and there is a need to address their specific requirements. Recent studies show that, in comparison to HRT, tibolone is as effective in alleviating menopausal symptoms and preventing bone loss, has a greater positive effect on sexual dysfunction and is associated with less vaginal bleeding, but it is rarely mentioned in guidelines for menopausal treatment. Levels of awareness amongst women about treatments for menopausal symptoms vary between Asian countries but, even in countries where awareness is high, HRT usage is much lower than in the West. To provide a practical approach to the use of tibolone in Asian postmenopausal women, a panel of experts in the management of menopause from 11 Asia Pacific countries has developed recommendations for its use, based on the evidence from clinical studies published since 2005. However, as much of the clinical data reviewed are from international studies, the recommendations and the treatment algorithm presented here are widely applicable.

Hormone replacement therapy use and variations in the risk of breast cancer

OBJECTIVE

To determine the effect of different types and formulations of hormone replacement therapy (HRT) on the risk of breast cancer in postmenopausal women.

DESIGN

Population-based case-control study.

SETTING

UK, 1988-2004.

PARTICIPANTS

Women 50-75 years between 1998 and 2004.

MAIN OUTCOME MEASURES

Breast cancer incidence to estimate the rate ratio (RR) associated with use of various HRTs over a 30-year period.

RESULTS

We identified 6347 incident cases of breast cancer that were matched with 31,516 controls. Cases were on average 61 years at diagnosis and 22% had undergone a hysterectomy. The rate of breast cancer was increased with the use of opposed estrogens in oral form (adjusted RR 1.38; 95% CI 1.27-1.49) in contrast to patch form (RR 1.08; 95% CI 0.81-1.43). This rate was similarly elevated with both continuous (RR 1.29; 95% CI 1.07-1.56) and sequential (RR 1.33; 95% CI 1.21-1.46) forms of opposed estrogen. The rate of breast cancer was not increased among exclusive users of unopposed estrogens (RR 0.97; 95% CI 0.86-1.09) or of tibolone (RR 0.86; 95% CI 0.65-1.13). Users of tibolone who had switched from opposed estrogens, however, had an elevated rate (RR 1.29; 95% CI 1.09-1.52). The rate of breast cancer increased by 25% (95% CI 20-30%) with every ten prescriptions of orally administered opposed estrogen.

CONCLUSIONS

The risk of breast cancer varies with the formulation and preparation of HRT. Opposed estrogens (progesterone-estrogen) in oral form are associated with an increased risk of breast cancer, which increases with use. Transdermal opposed estrogens, unopposed estrogens and tibolone do not increase this risk. However, this study is an observational study that carries risks of various biases, and thus the findings need to be interpreted with caution.

Postmenopausal HRT and tibolone in relation to muscle strength and body composition

OBJECTIVES

Sarcopenia, the loss of muscle mass with age, has a great impact on physical function, and especially in postmenopausal women, who experience a greater decline in muscle strength than do men of similar age. Conventional hormone replacement therapy (HRT) may diminish this loss of muscle strength and may even increase muscle strength. However, HRT is not currently promoted for this indication because of its negative side effects, which is why tibolone, a synthetic steroid with oestrogenic, progestogenic, and androgenic activity, may be an alternative option. The aim of this article was to review data on the effect of HRT and tibolone on muscle strength and body composition in postmenopausal women.

METHODS

Medline, Pubmed, Embase, and Sumsearch were searched for articles on the effect of HRT and tibolone on muscle strength and body composition, using the Mesh terms hormone replacement therapy and clinical trial combined with muscle strength or body composition. Tibolone was added as search term with clinical trial and muscle strength or body composition.

RESULTS

Three of five randomized controlled trials reported a significant positive effect of HRT on muscle strength but not on body composition. Tibolone significantly increased handgrip strength and isometric knee extension strength in one randomized placebo-controlled, double-blind trial and increased mean knee extensor strength in one cross-sectional study. Tibolone also increased the lean body mass and decreased the accumulation of body fat.

CONCLUSIONS

HRT and tibolone increase muscle strength. Unlike HRT, tibolone also increases lean body mass and significantly reduces the total body fat content. Further research is recommended to determine whether tibolone is a safe treatment for sarcopenia.