Flutamide is an oral antiandrogen drug primarily used to treat prostate cancer. It competes with testosterone and its powerful metabolite, dihydrotestosterone (DHT) 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 side-effect profile. Flutamide may also be used to treat excess androgen levels in women. It is marketed by Schering-Plough under the brand name Eulexin.
Structure
Unlike the hormones with which it competes, flutamide is not a
steroid; rather, it is a substituted
anilide. After absorption, the molecule is quickly α-hydroxylated to its primary active form, hydroxyflutamide. Flutamide is excreted in various forms in the
urine, the primary form being 2-amino-5-nitro-4-(trifluoromethyl) phenol.
Use in prostate cancer
Gonadotropin-releasing hormone (GnRH) is released by the
hypothalamus in a
pulsatile fashion; this causes the anterior
pituitary to release
leutinizing hormone (LH) and
follicle-stimulating hormone (FSH). LH stimulates the
testes to produce testosterone, which is metabolized to DHT by the enzyme
5α-reductase.
DHT, and to a much smaller extent, testosterone, stimulate prostate cancer cells to grow. Therefore, blocking these
androgens can provide powerful treatment for prostate cancer, especially
metastatic disease. Normally administered are
analogues of GnRH, such as
leuprolide or
goserilin. Although they stimulate the same receptors that GnRH does, since they are present continuously and not in a pulsatile manner, they serve to inhibit the pituitary and therefore block the whole chain. However, they initially cause a surge in activity; this is not solely a theoretical risk but may cause the cancer to flare. Flutamide was initially used at the beginning of GnRH-analogue therapy to block this surge, and it and other nonsteroidal anti-androgens continue in this use.
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