Information about Antiandrogens
The antiandrogens are medications that act by binding to intracellular androgen receptors, preventing the effects of endogenous androgens on target tissues such as testes, hair follicles, hypothalamus, pituitary, ovaries and prostate gland.
Mechanism of action of Antiandrogens
The antiandrogens are used for a variety of hyperandrogenic states such as acne, hirsutism, and paraphilias, but their major use is in therapy of prostate cancer. Chemically, antiandrogens are classified into steroidal (such as cyproterone acetate) and nonsteroidal (including flutamide, nilutamide and bicalutamide). Cyproterone, despite evaluation in many clinical trials, has yet to receive FDA approval for use the United States, largely because of its potential for hepatotoxicity. In contrast, flutamide, nilutamide and bicalutamide are now approved and in general clinical use for therapy of prostate cancer. The largest and longest clinical experience has been with flutamide which has been shown to produce clinical remission in patients with prostate cancer, and is also used in hyperandrogenic states including acne and hirsutism. Nilutamide has been extensively studied and is indicated for use in combination with surgical castration for the treatment of metastatic prostate cancer and is recommended to be started at the time of orchiectomy. Unlike flutamide, nilutamide has not been evaluated in detail as therapy of hirsutism or acne. Bicalutamide, the most recent antiandrogen to be approved for use in the United States, is also used in therapy of prostate cancer, but has not been approved for use in nonmalignant hyperandrogenic states.
Liver safety of Antiandrogens
All three nonsteroidal antiandrogens have been linked to instances of liver injury. Minor asymptomatic elevations in serum aminotransferase levels occur in 10% to 62% of patients on long term antiandrogen therapy, and prominent elevations (3 to 5 times the ULN) in 1% to 10%, the rates being somewhat higher for flutamide than nilutamide or bicalutamide. Instances of acute hepatitis with jaundice and even acute liver failure have been reported with all three antiandrogens. While most reports have related to flutamide, this may be due to its more extensive use. The rate of clinically apparent acute liver injury during prolonged antiandrogen therapy is reported to be as high as 9%, but is probably in the range of 0.1% to 1%. Screening for serum aminotransferase levels during the first few months of therapy is often recommended, but the effectiveness of this approach in preventing serious liver injury and death has not been shown.
Abiraterone is a more recently developed antiandrogen used to treat prostate cancer. Abiraterone is a steroid inhibitor of CYP17, an enzyme in the pathway of androgen production which has been shown to be effective in prolonging relapse free and overall survival in men with metastatic, castration-resistant prostate cancer. Abiraterone has been linked to a moderate rate of serum aminotransferasae elevations during therapy, but the abnormalities are usually mild and transient, and instances of clinically apparent liver injury have not been linked to use of this agent, although its general use has been limited.
The following are links to each drug record.