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Finasteride, a novel 4-azasteroid, is a breakthrough in the treatment and control of benign prostatic hyperplasia. Mechanistically, it inhibits the prostatic-specific enzyme 5-alpha reductase, thereby decreasing the conversion of testosterone to dihydrotestosterone. It is reportedly effective in reducing urinary symptoms and prostatic volume and increasing maximal urinary flow rate. Finasteride is also being investigated as a treatment for prostatic cancer.

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White or off-white crystalline powder. Soluble in chloroform, dimethyl sulfoxide, ethanol, methanol, or n-propanol. Insoluble in propylene glycol or polyethylene glycol 400. Very slightly soluble in 0.1mol/L hydrochloric acid, 0.1mol/L sodium hydroxide solution, or water.

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Finasteride is an antialopecia agent that Inhibitor of 5α-reductase, the enzyme which converts testosterone to the more potent androgen, 5α-dihydrotestosterone. It is used to treatment of benign prostatic hyperplasia and androgenetic alopecia.

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ChEBI: Finasteride is an aza-steroid that is a synthetic drug for the treatment of benign prostatic hyperplasia. It has a role as an androgen antagonist, an EC 1.3.1.22 [3-oxo-5alpha-steroid 4-dehydrogenase (NADP(+))] inhibitor and an antihyperplasia drug. It is an aza-steroid, a 3-oxo steroid and a delta-lactam. It derives from a hydride of a 5alpha-androstane.

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Finasteride is a specific inhibitor of steroid type II 5α-reductase, an intracellular enzyme that converts testosterone to DHT. By inhibiting type II 5α-reductase, this conversion is blocked, resulting in significant decreases in serum and tissue DHT concentrations. Merck & Co. developed finasteride as an oral treatment for androgenetic alopecia after men taking finasteride (5 mg/ day) for prostate enlargement noticed regrowth of their hair. Finasteride is indicated for use in men only. Women of childbearing age cannot take finasteride because it may cause hypospadia (a developmental abnormality of the penis) in the male offspring if taken during pregnancy.

Indications

Finasteride (Proscar) is a 5-reductase inhibitor that blocks the conversion of testosterone to DHT in target tissues. Since DHT is the major intracellular androgen in the prostate, finasteride is effective in suppressing DHT stimulation of prostatic growth and secretory function without markedly affecting libido. It is approved for the treatment of benign prostatic hyperplasia. Although there is usually some regression in the size of the prostate gland following administration of finasteride, clinical response may take 6 to 12 months. If the obstructive symptoms are severe, there is often not enough time to allow this compound to work.The principal adverse effects of finasteride are impotence, decreased libido, and decreased volume of ejaculate. The compound is generally well tolerated in men.

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Antiandrogen that inhibits type II 5 α reductase (IC 50 = 65 nM). Suppresses the conversion of testosterone to dihydrotestosterone. Reduces prostatic dihydrotestosterone levels and prostate size in vivo . Orally active.

Pharmacokinetics

The mean oral bioavailability of finasteride is 65%, as shown in Table 45.4, and is not affected by food. Approximately 90% of circulating finasteride is bound to plasma proteins. Finasteride has been found to cross the blood-brain barrier, but levels in semen were undetectable (<0.2 ng/mL). Finasteride is extensively metabolized in the liver, primarily via CYP3A4 to two major metabolites: monohydroxylation of the t-butyl side chain, which is further metabolized via an aldehyde intermediate to the second metabolite, a monocarboxylic acid. The metabolites show approximately 20% the inhibition of finasteride for 5α-reductase. The mean terminal half-life is approximately 5 to 6 hours in men between 18 and 60 years of age and 8 hours in men older than 70 years of age. Following an oral dose of finasteride, approximately 40% of the dose was excreted in the urine as metabolites and approximately 57% in the feces. Even though the elimination rate of finasteride is decreased in the elderly, no dosage adjustment is necessary. No dosage adjustment is necessary in patients with renal insufficiency. A decrease in the urinary excretion of metabolites was observed in patients with renal impairment, but this was compensated for by an increase in fecal excretion of metabolites. Caution should be used during administration to patients with liver function abnormalities, because finasteride is metabolized extensively in the liver.

Clinical Use

The selective inhibition of the type 2 5α-reductase isozyme produces a rapid reduction in plasma DHT concentration, reaching 65% suppression within 24 hours of administering a 1-mg oral tablet (106). At steady state, finasteride suppresses DHT levels by approximately 70% in plasma and by as much as 85 to 90% in the prostate. The remaining DHT in the prostate likely is the result of type 1 5α-reductase. The mean circulating levels of testosterone and estradiol remained within their physiological concentration range. Long-term therapy with finasteride can reduce clinical significant end points of BPH, such as acute urinary retention or surgery. Finasteride is most effective in men with large prostates. Finasteride has no affinity for the AR and no androgenic, antiandrogenic, estrogenic, antiestrogenic, or progestational effects.

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Perifollicular fibrosis: Pathogenetic role in androgenetic alopecia; H.G. Yoo, et al.; Biol. Pharm. Bull. 29, 1246 (2006). DOI:10.1248/BPB.29.1246
Finasteride induces apoptosis via Bcl-2, Bcl-xL, Bax and caspase-3 proteins in LNCaP human prostate cancer cell line: J.M. Golbano, et al.; Int. J. Oncol. 32, 919 (2008) DOI:10.3892/IJO.32.4.919
Steroid 5α-reductase as a novel therapeutic target for schizophrenia and other neuropsychiatric disorders: S. Paba, et al.; Curr. Pharm. Des. 17, 151 (2011) DOI:10.2174/138161211795049589
Finasteride: An update of its use in the management of symptomatic benign prostatic hyperplasia (a review). M. I. Wilde, K. L. Goa, Drugs 1999, 57, 557. DOI:10.2165/00003495-199957040-00008
Finasteride: a review of its use in male pattern hair loss. K. J. McClellan, A. Markham, Drugs 1999, 57, 111. DOI:10.2165/00003495-199957010-00014
Type 1 and type 2 5α-reductase expression in the development and progression of prostate cancer (a review). L. N. Thomas, R. C. Douglas, C. B. Lazier, C. K. L. Too, R. S. Rittmaster, D. J. Tindall, Eur. Urol. 2008, 53, 244. DOI:10.1016/J.EURURO.2007.10.052

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