The idea of hormone replacement therapy (HRT) is to provide oestrogen replacement in as physiological a way possible – that is to mimic the body’s own hormone production.
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The main ways in which HRT is given are:
Oral – by mouth
Across the skin – percutaneous – as gels or patches
As implants
As a nasal spray
As an injection
In a hormone impregnated intrauterine device
Via the vagina as creams, foams, pessaries or oestrogen impregnated rings
Oral preparations
This is the most common and best known form of HRT and the one with which there is the most clinical experience.
The advantages of these methods are that they are:
Cheap
Easy to take
There is a wide choice of different preparations
Oral progestins can be given at the same time
Oral oestrogen raises levels of HDL – the “good” form of cholesterol
As with any drug, there are disadvantages associated with this form of oestrogen:
A daily tablet is needed
A relatively high dose of the active ingredients is needed because around 30% of the active oestrogen is lost when the drug is broken down in the liver
There is variation in the way in which the oestrogen is absorbed in the gut
There is poor absorption if there are any problems with the gut
The functions of the enzymes in the liver are altered
Triglyceride levels can be raised
All the tablets contain lactose which can be a problem for women who are lactose intolerant
Oestrogen gels
Oestrogen gels are a popular choice of HRT among some women. This form of oestrogen replacement comes as a skin cream which is applied daily. The amount of oestrogen delivered depends on the amount of the cream used, which allows quite a wide choice of different doses.
There is a low incidence of skin reactions.
A potential problem with gels is that they contain only oestrogen so they cannot be used by women who still have their womb.
Patches
Non-oral oestrogen bypasses the problems of loss within the liver, so more oestrogen is delivered where it is needed.
The original patches were called matrix patches, and were alcohol-based. This caused skin reactions in some women. New patches deliver oestrogen as effectively as the originals, but do not contain alcohol so they cause fewer skin reactions.
Patches are available with a progestin added for 14 days each month, or as a continuous/combined single oestrogen plus progestin regimen.
The patches are usually replaced twice a week. There is also a preparation which can be replaced once a week.
The patches particularly suit women who:
Are lactose intolerant
Have a history of blood clots
Have experienced problems with oral HRT
Have difficulty with hot flushes and similar symptoms of menopause which have not been controlled by oral HRT
Are diabetic
Have high triglyceride levels, particularly if they are overweight
Suffer from vascular headaches such as migraines
Have liver disease
Vaginal oestrogens
Oestrogen is available as a vaginal cream, as a pessary which can be inserted into the vagina and as a low-dose vaginal ring.
The vaginal route of administration is particularly useful for women who cannot use either oral oestrogen, skin creams or patches because they need very low doses of oestrogen due to particular risk factors such as breast cancer.
The vaginal ring in particular, delivers a very low dose of oestrogen over a period of a month, with very little absorption in the rest of the body.
This is useful where the main postmenopausal complaints are related to thinning of the vaginal walls and to problems with the urinary tract. The oestrogen which is made available to the tissue from the vaginal ring can counteract vaginal dryness and constant urinary tract infections.
Implants
These have been around for a while, but are controversial. They are little pellets containing oestrogen which are surgically implanted under the skin – usually in the upper arm or in the buttocks – where the hormones are broken down and delivered to the system at variable rates.
The main problems with this method of delivery are that a surgical procedure is needed and that something called tachyphlaxis occurs. Tachyphylaxis is the lessening of effects produced by a particular drug during continuous use. This means that the effects of the oestrogen become weaker with time and the implant needs to be constantly replaced.
Implants should be replaced no less than every six months, or when the level of oestrogen falls below certain levels.
Because the oestrogen from the implants can stimulate the endometrium (lining of the womb) which cannot be easily controlled even by removing the implants, many people do not recommend their use in women who have an intact womb.
Tibolone
Tibolone is an oestrogen mimic, which mimics the steroid hormones produced by the ovaries. It has properties which are similar to oestrogen, progesterone and the androgens such as testosterone. It is very effective for preventing bone loss and treating hot flushes. It also prevents vaginal dryness and seems to have a positive effect on libido.
Because it is not an oestrogen, it does not have the bad effects on the endometrium which oestrogen has. In fact it causes the endometrium to decrease in thickness. It may also have protective effects against breast cancer since it stops the increase in size and number of breast cells. This effect needs to be researched further before definite answers are available.
The main disadvantage of tibolone is that it tends to reduce HDL-cholesterol in the short term. However, just how much effect this has on coronary artery disease is not known.
The main advantage of tibolone is that women seldom bleed while taking the drug. But this is only true if it is started at least one year after the final menstrual period.
A recent Canadian study has found that almost a quarter of women ovulate more than once every 28 days, which is why the rhythm method is ineffective as contraception for many couples.
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