Finasteride

Absorption

Finasteride is well absorbed following oral administration and displays a slow accumulation phase after multiple dosing.[lablel] In healthy male subjects receiving oral finasteride, the mean oral bioavailability was 65% for 1 mg finasteride and 63% for 5 mg finasteride, and the values ranged from 26 to 170% for 1 mg dose and from 34 to 108% for 5 mg dose, respectively. It is reported that food intake does not affect the oral bioavailability of the drug. The peak plasma concentrations (Cmax) averaged 37 ng/mL (range, 27-49 ng/mL) and was reached 1-2 hours post administration. The AUC(0-24 hr) was 53 ngxhr/mL (range, 20-154 ngxhr/mL). The plasma concentrations and AUC are reported to be higher in elderly male patients aged 70 years or older.

Toxicity

LD50
Oral LD50 is about 418 mg/kg in rats and there have been cases of lethality in rats receiving a single oral dose of 400 mg/kg in males and 1000 mg/kg in females.
Nonclinical toxicology
In a 24-month rat study, there were no signs of the tumorigenic potential of finasteride. In a 19-month carcinogenicity study in CD-1 mice, high doses of finasteride, at 1824 times the human exposure (250 mg/kg/day), resulted in an increase in the incidence of testicular Leydig cell adenomas and an increase in serum LH levels. In vitro mutagenesis assays demonstrated no evidence of mutagenicity. In an in vitro chromosome aberration assay, using Chinese hamster ovary cells, there was a slight increase in chromosome aberrations with much higher doses of finasteride.
Overdose
There were no reported significant adverse events in clinical trials of male patients receiving single oral doses of finasteride up to 400 mg and multiple doses of finasteride up to 80 mg/day for three months. As there have been no cases of overdose or clinically significant toxicity with finasteride, there are no specific recommendations in case of an overdose.
Significant adverse events
Common reproductive adverse events seen with finasteride therapy include erectile dysfunction, ejaculatory dysfunction, and loss of libido. These adverse events tend to disappear after discontinuation or chronic use of the drug. Only causal adverse event occurring at the male reproductive system that is caused by finasteride is decreased ejaculatory volume because of the predominant action of DHT on the prostate.
Special populations
Finasteride can be safely used in elderly patients or those with renal impairment with no specific dosing adjustment recommendations. Finasteride is indicated for male patients only, and it is advised that exposure to finasteride is avoided in pregnant women carrying male fetuses as it may lead to abnormal development of external genitalia in male fetuses.

Description

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.

Description

Since 1997, finasteride has been marketed under many trade names (Propecia is the most prominent) for reversing the effects of male pattern hair loss. But before that—in 1992—it was approved by the US Food and Drug Administration for treating benign prostatic hyperplasia (enlarged prostate gland) and prostate cancer. In 2008, the Swedish Medical Academy advised users that finasteride may have persistent sexual side effects.

Chemical properties

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.

Originator

Merck (U.S.A.)

The Uses of Finasteride

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.

Indications

Finasteride is indicated for the treatment of symptomatic benign prostatic hyperplasia (BPH) in men with an enlarged prostate to improve symptoms, reduce the risk of acute urinary retention, and reduce the risk of the need for surgery including transurethral resection of the prostate (TURP) and prostatectomy. A combination product with tadalafil is also used for the symptomatic treatment of BPH for up to 26 weeks.
Finasteride is also indicated for the treatment of male pattern hair loss (androgenetic alopecia, hereditary alopecia, or common male baldness) in male patients.

Background

Finasteride is a synthetic 4-azasteroid compound and specific inhibitor of steroid Type II 5α-reductase, which is an intracellular enzyme that converts the androgen testosterone into 5α-dihydrotestosterone (DHT). It works in a similar fashion as dutasteride, which is another 5-alpha-reductase inhibitor, by exerting antiandrogenic effects. Finasteride is an orally active drug that was first approved by the FDA in 1992 for the treatment of benign prostatic hyperplasia to improve symptoms and reduce the risk for acute urinary retention or the need for surgical procedures. In 1998, it was approved by the FDA to treat male pattern hair loss. Finasteride is commonly marketed under the brand names Propecia and Proscar to be used aloneo or in combination with doxazosin, an alpha-blocker.
Both benign prostatic hyperplasia and androgenic alopecia are androgen-dependent disorders that are characterized by in situ high levels of DHT. In the treatment of benign prostate hyperplasia, alpha-blockers such as tamsulosin and terazosin are also used. Compared to alpha-blockers that focus on providing the rapid relief of symptoms, 5α-reductase inhibitors aim to target the underlying disease by blocking the effects of the primary androgen involved in benign prostate hyperplasia and androgenic alopecia, thus reducing the risk for secondary complications while providing symptom control.

What are the applications of Application

Finasteride is an antiandrogen that inhibits 5α-Reductase 2

Definition

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.

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.

What are the applications of Application

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.

Manufacturing Process

In a flask equipped with an overhead stirrer, a nitrogen inlet, and reflux condenser was placed 840 ml of dry THF and 20.0 g of 17β-carboxylate 17β- carbomethoxy ester of 4-aza-5α-androst-1-en-3-one (synthesized according to Patent US 4,377,584, issued Mar. 22,1883, and J. Med. Chem., 29, 2298 (1986)). The resulting slurry was cooled to -5-10°C, and 27.6 mL of tbutylamine was added. A solution of ethylmagnesium bromide in THF (122 mL, 2 M) was added maintaining the temperature of the reaction mixture below 10°C. The reaction mixture was heated at reflux for 12 hours and was added to a cold (10°C) solution of 25% ammonium chloride in water. The mixture was warmed to 25°C and allowed to settle. The THF solution was separated and concentrated by atmospheric distillation to 200 mL and the product was crystallized by adding approximately 600 mL of dilute aqueous HCl. The resulting white solid was isolated by filtration and was dried at 70°C under vacuum to give 21.7 g (97% yield) 2-butyl-1-(4-carboxybenzyl)-4- chloroimidazole-5-acetic acid of finasteride. The finasteride can be purified by conventional procedures, e.g. recrystallization from methylene chloride/ethyl acetate or acetic acid/water, melting point 261°C.

brand name

Proscar

Therapeutic Function

Antineoplastic

Biological Activity

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.

Biochem/physiol Actions

Selective 5α-reductase inhibitor; antiandrogen.

Pharmacokinetics

Finasteride is an antiandrogenic compound that works by suppressing the production of serum and intraprostatic dihydrotestosterone (DHT) in men via inhibiting the enzyme responsible for the biosynthesis of DHT. The maximum effect of a rapid reduction in serum DHT concentration is expected to be observed 8 hours following administration of the first dose. In a single man receiving a single oral dose of 5 mg finasteride for up to 4 years, there was a reduction in the serum DHT concentrations by approximately 70% and the median circulating level of testosterone increased by approximately 10-20% within the physiologic range. In a double-blind, placebo-controlled study, finasteride reduced intraprostatic DHT level by 91.4% but finasteride is not expected to decrease the DHT levels to castrate levels since circulating testosterone is also converted to DHT by the type 1 isoenzyme expressed in other tissues. It is expected that DHT levels return to normal within 14 days upon discontinuation of the drug. In a study of male patients with benign prostatic hyperplasia prior to prostatectomy, the treatment with finasteride resulted in an approximate 80% lower DHT content was measured in prostatic tissue removed at surgery compared to placebo. While finasteride reduces the size of the prostate gland by 20%, this may not correlate well with improvement in symptoms. The effects of finasteride are reported to be more pronounced in male patients with enlarged prostates (>25 mL) who are at the greatest risk of disease progression.
In phase III clinical studies, oral administration of finasteride in male patients with male pattern hair loss promoted hair growth and prevented further hair loss by 66% and 83% of the subjects, respectively, which lasted during two years' treatment. The incidences of these effects in treatment groups were significantly higher than that of the group receiving a placebo. Following finasteride administration, the levels of DHT in the scalp skin was shown to be reduced by more than 60%, indicating that the DHT found in scalp is derived from both local DHT production and circulating DHT. The effect of finasteride on scalp DHT is likely seen because of its effect on both local follicular DHT levels as well as serum DHT levels.. There is evidence from early clinical observations and controlled studies that finasteride may reduce bleeding of prostatic origin.

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.

Veterinary Drugs and Treatments

Finasteride may be useful in treating the benign prostatic hypertrophy in canine patients. Because of the drug’s relative expense and the long duration of therapy required to see a response, its usefulness may be limited in veterinary medicine.
It may also be useful in the adjunctive treatment of adrenal disease in ferrets.

Metabolism

Finasteride undergoes extensive hepatic metabolism predominantly mediated by the cytochrome P450 3A4 (CYP3A4) enzyme to form the t-butyl side chain monohydroxylated and monocarboxylic acid metabolites. Theses metabolites retain less than 20% of the pharmacological activity of the parent compound.

Metabolism

Finasteride is metabolised primarily via the cytochrome P450 3A4 enzyme subfamily. Following an oral dose of 14C-finasteride in man, two metabolites of the drug were identified that possess only a small fraction of the 5α-reductase inhibitory activity of finasteride. 39% of the dose was excreted in the urine in the form of metabolites (virtually no unchanged drug was excreted in the urine) and 57% of total dose was excreted in the faeces.

storage

Store at RT

References

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