Temporary chemical castration is the depletion of male hormones called androgens, which include the hormone testosterone. As such, the therapy is also called androgen deprivation therapy. The therapy is typically used to treat certain cancers or to delay early puberty. Various drugs have been created to achieve androgen deprivation.
Hormone Agonists
Signals from the brain and pituitary cause the testes to make androgens. The drugs leuprolide, goserelin and triptorelin bind to receptors in the brain, signalling them to release the hormones that increase androgen levels according to "Basic and Clinical Pharmacology" by Bertram Katzung. As a result, for over a week the androgen levels will rise. However, after this time, fewer and fewer receptors become available and androgen levels fall. The initial rise in androgens may cause worsening of the condition being treated, such as bone or urinary obstruction in prostate cancer. As the levels of hormones fall, other side effects may occur. These include allergic reactions, nausea, weight gain, headaches, hot flashes and osteoporosis.
Hormone Antagonist
Degarelix binds to the same receptors as the drugs above, but has a slightly different mechanism of action. It blocks the receptors, preventing the brain from releasing hormonal signals to the testes. As a result, there is no initial surge of hormones, which may be preferable to avoid symptoms such as bone pain during the first week of therapy. Side effects are similar to those above.
Antiandrogens
Alternatively, drugs may be given to block the effects of testosterone and other androgens in the body. These drugs work by binding to receptors in the cells that normally bind testosterone, thus blocking testosterone from binding. The receptors are not activated, and androgens will not affect the body. Examples of these drugs include cyproterone acetate, bicalutamide, nilutamide and flutamide. Side effects include enlargement of breast tissue, decreased sexual desire and mood swings.
References
- "Harrison's Principles of Internal Medicine"; Anthony S. Fauci; 17th Edition 2008
- "Basic and Clinical Pharmacology" Bertram Katzung et al; 17th Ed 2009
