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MENOPAUSE AND HORMONE REPLACEMENT THERAPY (HRT): TYPES OF HRT

HRT preparations may be administered by mouth, as a skin cream, as a skin patch, as an implant or by vaginal creams and pessaries.

Oestrogens can be either natural or synthetic. Natural oestrogens are of animal origin, the commonest source being pregnant mares. These animals supply oestrogen in the form of equilin and equilenin. The equilin, in the form of sodium equilin sulphate, is paired (conjugated) with sodium oestrone sulphate to produce the commonly prescribed preparation Premarin.

Synthetic oestrogens are chemically dissimilar to their natural cousins and tend to have a more profound effect on the liver proteins, producing greater changes in blood clotting and blood lipid levels. Such products, for example ethinyl oestradiol, should therefore not be used for HRT.

Oral therapy

This is at present the commonest method of administration in the US and UK. By this means the hormone is taken, immediately after absorption, into the bloodstream and then to the liver, where up to one-third is converted to the less potent oestrone and oestriol. Higher doses consequently need to be given to achieve a satisfactory therapeutic blood oestradiol level. Nausea is often reported by those who take HRT by mouth.

The higher doses required by this method of administration can also influence liver metabolism, producing a rise in the sex hormone binding globulin, a sensitive indicator of liver protein function. Changes in triglyceride levels, with a rise in the VLDLs and a decrease in the antithrombin blood-clotting factor, may occur. These changes, which are dose-related, are seen when oral oestrogen is used in either the 17B-oestradiol form or the conjugated equine variety, but are more likely to occur with the latter.

Skin patch

When 17B-oestradiol, the natural oestrogen closest to human oestrogen, is administered transdermally, or by skin patch, nausea is rare, and the passage of the drug through the liver is avoided. There are no changes in the sex hormone binding globulin, or to the blood lipids or clotting factors. The skin patch was introduced to the UK in the mid-1980s under the brand name Estraderm. It consists of four layers: an outer transparent layer, a drug reservoir, a polymer membrane, and an adhesive outer rim. A continuous controlled amount of 17B-oestradiol is delivered through the skin at a rate sufficient to produce pre-menopausal blood oestradiol levels. The patch, which comes in three strengths (25, 50 and 100 micrograms, indicating relative absorption within a 24-hour period), needs changing every three to four days.

About 5 per cent of skin patch users report skin irritation and itching at the site of application, caused by the adhesive rim on the patch disc, not the drug. Another 5 per cent find that the patch loosens at the edges before it is time to change it, while approximately 10 per cent of users report difficulty in taking the disc off its backing prior to application.

Implants

Subcutaneous implants of 17B-oestradiol were first used in the 1960s. Now perfected, they are offered by many clinics, especially in the UK. This method of delivery also avoids the passage of the oestrogen through the liver. Implants last from three to six months, the reappearance of menopausal symptoms indicating when another implant is required. The implant, which is about the size of a small pea, is inserted in the fatty tissue below the skin surface of the abdominal wall or the thigh, under local skin anaesthetic. The small pellet, 25, 50 or 100 mg in strength, releases a continuous supply of oestradiol.

Occasionally a small quantity of the male hormone testosterone is combined with the oestradiol to increase sexual drive in cases where reduced libido is a significant problem at the menopause. (Testosterone should not be taken by mouth as it may adversely affect the liver.)

Major swings in the blood oestradiol level can occur with implant usage. Menopausal symptoms may reappear when oestradiol blood levels are normal: this occurrence is called 'tachyphylaxis' and may indicate either poor absorption of the oestradiol in the areas where it is taken up, or a developing dependency on oestradiol itself, though there is no evidence of oestradiol addiction. Careful and frequent monitoring of blood oestradiol levels is required so that a level of about 250 pico mols per litre can be maintained (a level similar to the mid-proliferative phase of the normal menstrual cycle). For some women monitoring can be inconvenient, because it involves frequent visits to the clinic for blood tests.

Skin creams

Skin creams (percutaneous application) are used on sites where there is a lot of fatty tissue (abdominal wall, hips, buttocks and thighs) and are very effective, but are not widely used outside France. They have been overtaken by the popularity, and effectiveness, of transdermal application (the skin patch).

Vaginal creams and pessaries

These allow oestrogen to be readily supplied to, and rapidly absorbed by, the target area. However, absorption is reduced when the vaginal wall has atrophied. Substantial amounts are required initially, but as improvement occurs (for example, fewer hot flushes are experienced) applications can be reduced to two or three times weekly or even less.

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