Antiandrogen

An anti-androgen, (or androgen antagonist) is any of a group of hormone antagonist compounds that are capable of preventing or inhibiting the biological effects of androgens, (male sex hormones) on normally responsive tissues in the body, which maintain male secondary sex characteristics. When the tissues do not respond normally to androgens, this is known as Androgen Insensitivity Syndrome.

Anti-androgens preferentially block the appropriate receptors, competing for binding sites on the cell's surface, effectively inhibiting the androgens' pathway. The effect of this is to lower the overall "free-testosterone" level within the body and thus when used in conjunction with estrogen Therapy in hormone replacement therapy (HRT) allows the estrogen to act in feminising the body. In the instance that puberty has either just started or is in progress, a strong anti-androgen will either reduce, or in some cases, stop the further development of secondary sex characteristics. It will not however, reverse changes already done. An anti-androgen will also result in reduced activity or function of the accessory male sex organs, and hyposexuality (diminished sexual desire or libido).

Anti-androgens are often indicated to treat severe male sexual disorders, such as hypersexuality, (excessive sexual desire) "sexual deviation", and in hormonal therapy in prostate cancer, where there is a direct link between testosterone and the spread of cancer. They can also be used for treatment of benign prostatic hyperplasia (prostate enlargement), acne, androgenetic alopecia (male pattern baldness), and hirsutism (excessive hairiness). They can be found in several female contraceptive pills, specifically to reduce hirstuitism, which may result from medical conditions such as hormone imbalance or Polycystic Ovary syndrome.

Like all drugs used in HRT, they must be taken under supervision of a medical professional, as they can have long term effects on liver and sexual function (impotence, sterility).

Strong Anti-androgens

These two anti-androgens are most popular as primary treatment for HRT, Spironolactone and Cyproterone Acetate.

Spironolactone

Spironolactone (17-spirolactone corticosteroid) - is a a synthetic 17-spirolactone corticosteroid, which is a renal competitive aldosterone antagonist in a class of pharmaceuticals called potassium-sparing diuretics. It causes the kidneys to eliminate unneeded water and sodium from the body into the urine, but reduces the loss of potassium from the body. They used primarily to treat low-renin hypertension, hypokalemia, and Conn's syndrome, but have an added property when used for HRT, in that they act as an anti-androgen, suppressing testosterone levels.

Spironolactone is known amongst the following name brands. It is also made by a variety of generic drug producing companies.

• Aldactone (available in 25mg, 50mg and 100 mg tablets)
• Novo-Spiroton (available in 25mg or 100 mg tablets)
• Spiractin (available in 25mg or 100mg tablets)
• Spirotone (available in 25mg or 100mg tablets)

Cyproterone acetate

Cyproterone acetate is a very powerful anti-androgen which block the actions of testosterone (and by proxy, dihydrotestosterone) on tissues and prevents androgens from binding to them suppressing luteinizing hormone (hence reducing testosterone levels). Its main uses have been in treating prostate cancer, benign prostatic hyperplasia, priapism, hypersexuality. There is a confirmed medical link between long term usage of Cyproterone Acetate and liver toxicity and in some cases, has been associated with depressive mood changes in some patients, presumably due to androgen deprivation.

Abrupt withdrawal of cyproterone acetate can be harmful, and some makers of this drug recommend that the daily dose be reduced by no more than 50 mg, at intervals of several weeks. The primary concern is the manner in which cyproterone acetate affects the adrenal gland. Due to its glucocorticoid activity, high levels of cyproterone acetate may reduce ACTH, resulting in adrenal insufficiency if discontinued suddenly. In addition, although cyproterone acetate reduces androgen production in the gonads, it can increase adrenal androgen production, in some cases resulting in an overall rise in testosterone levels. Thus the sudden withdrawal of cyproterone acetate may result in undesirable androgenic effects. This is a particular concern because androgens, especially dihydrotestosterone, suppress adrenal function, further reducing cortisol production. In theory, 5-alpha-reductase inhibitors such as finasteride and dutasteride may be able to mitigate this effect somewhat by preventing the conversion of testosterone to the more potent DHT.

A paradoxical effect called antiandrogen withdrawal response (AAWR) occurs with certain prostate cancer cells which have genetic mutations in their androgen receptors. These altered androgen receptors can be stimulated, rather than inhibited, by cyproterone. In such cases, withdrawal of cyproterone results in a reduction in cancer growth, rather than the opposite.

This drug is not licensed for use throughout the world, but is common in Europe, where it is the preferred anti-androgen used in HRT. Cyproterone Acetate is known amongst the following name brands; Androcur, Cyprostat, Cyproteron, Procur, Cyprone, Cyprohexal, Ciproterona, Cyproteronum, Neoproxil, and Siterone. It is manufactured in 50mg and 100mg tablets.
Information on this drug may be found at UK electronic Medicines Compendium.[1]

Due to its anti-androgen effect, (to treat hirsutism) Cyproterone Acetate may also be combined with an Estrogen in some female contraceptives. Birth control pills are not suitable for use as HRT.

• Climen 2mg Cyproterone Acetate and 1mg Estradiol Valerate
• Diane 35, Ginette 35 2mg of Cyproterone acetate and 0.035mg of Ethinyl Estradiol

Weaker Anti-androgens

There are a class of anti-androgens, less commonly used in HRT, due to their weaker anti-androgen effect. They do not lower testosterone levels but rather prevent testosterone and dihydrotestosterone (DHT) from binding to androgen receptors and because these have a weak action at the brain they do not lower libido or decrease erections and are generally used in Prostate Cancer treatment.

They are non-steroidal in their nature, all being derivatives with active Amine or Amide sites (N-H functional Groups) and are normally prescribed as part of an overall HRT reassignment regime.

Flutamide

Flutamide is sold in the form of 125mg tablets under the brands, Eulexin and Flutamide.
The drug is used in the treatment of prostate cancer. It competes with testosterone and dihydrotestosterone for binding to androgen receptors in the prostate gland. By doing so, it prevents them from stimulating the prostate cancer cells to grow. Flutamide has been largely replaced by a newer member of this class, bicalutamide, due to a better/less side-effects. More Information is available at RxList.[2]

Nilutamide

Nilutamide is sold in the form of 150mg tablets under the brands, Anandron (in Canada) and Nilandron. (in the United States)

The drug is used in the treatment of advanced stage prostate cancer. Nilutamide blocks the androgen receptor, preventing its interaction with testosterone. More Information is available at RxList.[3]

Bicalutamide

Bicalutamide, (marketed as Casodex, Cosudex, Calutide, Kalumid) is available in 50mg or 150mg tablets.

It was first launched in 1995 as a combination treatment (with surgical or medical castration) for advanced prostate cancer and subsequently launched as monotherapy for the treatment of earlier stages of the disease. It has grown in use both due to its effectiveness and the lower side effects that have been observed with other anti-androgen treatment of prostate cancer drugs. More Information is available at the website of the manufacture.[4]

Other androgen inhibitors

There are another group of chemical compounds used in conjunction with an accepted HRT regime. These class of compounds have very weak anti-androgen properties, but their suppression of dihydrotestosterone (DHT) has lead to successful hair regrowth in a number of patients with prolonged use.

They belong to a class of drugs called 5α(alpha)-reductase inhibitors, which block the action of the 5α-reductase isoenzymes that convert testosterone into DHT.

Finasteride

Finasteride is a weak anti-androgen which acts by inhibiting 5-α-reductase type II, the enzyme that converts testosterone to DHT. It is used to treat benign prostatic hypertrophy (BPH, enlargement of the prostate gland) in low doses, and some forms of prostate cancer in higher doses. It is registered in many countries for male-pattern baldness. Is sold in the form of 1mg tablets under the brands, Propecia and Proscar. (the latter also available in 5mg tablets) It is also available as a generic. More information may be found at the US National Institute of Health.[5]

Dutasteride

Dutasteride is sold under the brand Avodart, and is available in 0.5mg Capsules. It is used to treat conditions caused by DHT, such as benign prostatic hyperplasia, by blocking both 5-α-reductase type I and II. It also has hair regrowth properties.

See also

Androgen

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