What is the place of tibolone in HRT?
Q - What is the role of tibolone in HRT?
A - Tibolone is a steroid compound that combines oestrogenic, progestogenic and androgenic properties. It is an appropriate choice for HRT and is suitable for most postmenopausal women, but it is not the firstline and should be decided on a patient-by-patient basis.
Clinically, tibolone is as effective as oestrogen in relieving menopausal symptoms, including hot flushes and vaginal dryness. In addition it has been of proven benefit in increasing libido. Its endometrial safety and ability to prevent bone loss are comparable with continuous combined oestrogen-progesterone, with a lower rate of breakthrough bleeding.
Long-term studies on the effects of tibolone on fracture rates have not been done. The surrogate measure of bone mineral density show increases of the same magnitude as with alendronate.
The sum of the various biologic effects of tibolone and its metabolites on the cardiovascular system should neither increase nor decrease the risk of cardiovascular disease.
So far, there has been no indication of an increased risk of thromboembolism, but this is a potential side-effect that needs further study.
Tibolone lowers breast tissue concentrations of active oestrogen. It is not associated with an increased frequency of mastalgia.
Tibolone does not stimulate proliferation of breast cells; neither does it increase breast density on mammography. Data from the Organon clinical trial database phase II and III clinical trials suggested a reduced risk of breast cancer with tibolone compared with placebo. But the confidence intervals in these studies overlap unity and so may not be significant.
The recent Million Women Study suggested tibolone might be associated with an increased risk of breast cancer, though this was smaller when compared with combined oestrogen-progesterone.
Measures such as regular weight-bearing exercise, a calcium-rich diet and vitamin D supplements or bisphosphonates may be more appropriate for long-term prevention of osteoporosis.
On current evidence, tibolone seems a suitable alternative to combined oestrogen and progesterone with fewer side-effects and a more favourable risk-benefit profile.
It may also be an option in older women to help prevent fractures.
Mr Narendra Pisal and
Ms Theresa Freeman-Wang are consultant gynaecologists in the Department of Women's Health,
The Whittington Hospital, London