Finasteride

Finasteride (Proscar and Propecia (Merck), as well as generic names) is a synthetic 5-alpha-reductase inhibitor, an inhibitor of the enzyme that converts testosterone to dihydrotestosterone (DHT). Finasteride is approved for the treatment of benign prostatic hyperplasia (BPH) and male pattern baldness (MPB).

Medical uses

Benign prostatic hyperplasia

Physicians use finasteride for the treatment of benign prostatic hyperplasia (BPH) (also known as enlarged prostate). The usual dose is 5 mg once a day. Six months or more of treatment may be required to see the full effects of finasteride. If the drug is discontinued, any therapeutic benefits will be reversed. Finasteride may improve the symptoms associated with BPH such as difficulty urinating, getting up during the night to urinate, hesitation at the start of urination, and decreased urinary flow.^[1]

Male pattern baldness

In a 5-year study of men with mild to moderate hair loss, 2 out of 3 of the men who took 1 mg of finasteride daily regrew some hair, as measured by hair counts. In contrast, all of the men in the study who were not taking finasteride lost hair. In the same study, based on photographs that were reviewed by an independent panel of dermatologists, 48% of those treated with finasteride experienced visible regrowth of hair, and a further 42% had no further loss. Average hair count in the treatment group remained above baseline, and showed an increasing difference from hair count in the placebo group, for all five years of the study. Finasteride is effective only for as long as it is taken; the hair gained or maintained is lost within 6–12 months of ceasing therapy.^[2] In clinical studies, finasteride, like minoxidil, was shown to work on both the crown area and the hairline,^[3] but is most successful in the crown area.

Some users, in an effort to save money, buy Proscar (finasteride 5 mg) instead of Propecia, and split the Proscar pills into several parts to approximate the Propecia dosage.^[4] The pills are coated to prevent contact with the active ingredient during handling, and the dust or crumbs from broken Proscar tablets should be kept away from pregnant women or women who may become pregnant.^[5]

Adverse effects

Side effects of finasteride include impotence (1.1% to 18.5%), abnormal ejaculation (7.2%), decreased ejaculatory volume (0.9% to 2.8%), abnormal sexual function (2.5%), gynecomastia (2.2%), erectile dysfunction (1.3%), ejaculation disorder (1.2%) and testicular pain. According to the product package insert, resolution occurred in men who discontinued therapy with finasteride due to these side effects and in most men who continued therapy. The PPI also states that patients have reported persisting erectile dysfunction despite discontinuing the drug. In December 2010, Merck added depression as a side effect of finasteride.^[6]

Prostate cancer

The FDA has added warning to finasteride about an increased risk of high-grade prostate cancer.^[7] Whilst the potential for positive, negative or neutral changes to the potential risk of developing prostate cancer with finasteride has not been established, evidence has suggested it may temporarily reduce the growth and prevalence of benign prostate tumors, but could also mask the early detection of prostate cancer. The primary area for concern is for patients who may develop prostate cancer whilst taking finasteride for benign prostatic hyperplasia, which in turn could delay diagnosis and early treatment of the prostate cancer, thereby potentially increasing the risk of these patients developing high-grade prostate cancer.^[8]

The 2005 Prostate Cancer Prevention Trial (PCPT) showed at a dosage of 5 mg per day, as is commonly prescribed for BPH, participants taking finasteride were 25% less likely to have developed prostate cancer at the end of the trial compared to those taking a placebo.^[9] It appeared (incorrectly) that finasteride increased the specificity and selectivity of prostate cancer detection, thus creating an apparently increased rate of high Gleason grade tumor. A 2008 update of this study found that finasteride reduces the incidence of prostate cancer by 30%. In the original study, it turns out that the smaller prostate caused by finasteride means that a doctor is more likely to hit upon cancer nests and more likely to find aggressive looking cells. Most of the men in the study who had both low and high-grade prostate cancer chose to be treated, and many had their prostates removed. A pathologist then carefully examined each of those 500 prostates and compared the kinds of cancers found at surgery to those initially diagnosed at biopsy. This study concluded that finasteride did not increase the risk of high-grade prostate cancer.^[10][11]

Sexual side effects

There have been case reports of persistent diminished libido or erectile dysfunction, even after stopping the drug.^[12] In December 2008, the Swedish Medical Products agency concluded a safety investigation of finasteride and subsequently advised that the use of finasteride may result in irreversible sexual dysfunction. The Agency's updated safety information lists difficulty in obtaining an erection that persists indefinitely, even after the discontinuation of finasteride, as a possible side effect of the drug.^[13] The UK's Medical and Healthcare Products Regulatory Agency (MHRA) say that erectile dysfunction that persists once use of finasteride has stopped has been reported to them.^[14] Similar labeling changes have been made by the Italian government. For a period of time there was a discrepancy between European and North American warning labels regarding the risks of developing persistent sexual side effects from taking Propecia but after two years Merck revised the United States' warning label to report that they had received reports of patients facing "difficulty in achieving an erection that continued after stopping the medication".^[15]

Male breast cancer

In December 2009, the Medicines and Healthcare products Regulatory Agency in the UK announced new drug safety advice on finasteride and the potential risk of male breast cancer. The agency concluded that, although overall incidence of male breast cancer in clinical trials for finasteride 5 mg was not significantly increased, a higher risk of male breast cancer with finasteride use cannot be excluded. A warning on this risk will be included in the product information.^[16]

Teratogenicity

Finasteride is in the FDA pregnancy category X. This means that it is known to cause birth defects in an unborn baby. Women who are or who may become pregnant must not handle crushed or broken finasteride tablets, because the medication could be absorbed through the skin. Finasteride is known to cause birth defects in a developing male baby. Exposure to whole tablets should be avoided whenever possible, however exposure to whole tablets is not expected to be harmful as long as the tablets are not swallowed. It is not known whether finasteride passes into breast milk, and thus should not be taken by breastfeeding women. Finasteride may pass into the semen of men, but Merck states that a pregnant woman's contact with the semen of a man taking finasteride is not an issue for concern. Finasteride is known to affect blood donations, and potential donors are typically restricted for at least a month after their most recent dose.^[17]

Interference with doping assays

Many sports organizations have banned finasteride because it can be used to mask steroid abuse.^[18] Since 2005, finasteride has been on the World Anti-Doping Agency's list of banned substances. However, it was removed from the list in 2009.^[19] Notable athletes who used finasteride for hair loss and were banned from international competition include skeleton racer Zach Lund, bobsledder Sebastien Gattuso, footballer Romário and ice hockey goaltender José Théodore.^[20]

Mechanism of action

Testosterone in males is produced primarily in the testicles, but also in the adrenal glands. The majority of testosterone in the body is bound to sex hormone-binding globulin (SHBG), a protein produced in the liver that transports testosterone in the bloodstream, prevents its metabolism, and prolongs its half-life. Once it becomes unbound from SHBG, free testosterone can enter cells throughout the body. In certain tissues, notably the scalp, skin, and prostate, testosterone is converted into dihydrotestosterone (DHT) by the enzyme 5-alpha reductase. DHT is a more powerful androgen than testosterone (as it has a much higher affinity for the androgen receptor), so 5-alpha reductase can be thought to amplify the androgenic effect of testosterone in the tissues in which it's found. In addition to blocking the 5-alpha reductase enzyme, finasteride is a competitive inhibitor of the 5-beta reductase type 2 enzyme.^[21]

Finasteride is an inhibitor of 5-alpha reductase by being an aza analog of testosterone, thereby initially binding to 5-alpha reductase similarly to testosterone, but with the effect of remaining bound to it rather than being converted, thereby blocking the space that testosterone would otherwise have taken. By blocking 5-alpha reductase, finasteride blocks the conversion of testosterone into the more powerful androgen DHT. This reduces androgenic activity in the scalp, treating hair loss at its hormonal source. In the prostate, inhibition of 5-alpha reductase leads to a reduction of prostate volume, which improves the symptoms of benign prostatic hyperplasia (BPH) and reduces the risk of prostate cancer. Inhibition of 5-alpha reductase also leads to a reduction in the weight of the epididymis and a decrease in the percentage of motile and morphologically normal spermatozoa found in the epididymis.^[22]

By inhibiting 5AR in the central nervous system, finasteride has been shown to diminish the biosynthesis of neurosteroids, which require 5AR function. Neurosteroids and neuroactive steroids play a role in memory enhancement, sedative, hypnotic, anesthetic, anxiolytic, antistress, sleep modulating, anticonvulsant, and antidepressant properties. It has therefore been suggested that alterations in neurosteroid levels explain some of the mental and sexual side-effects of finasteride.^[12]

Preparations

Drug trade names include Propecia and Proscar, the former marketed for male pattern baldness (MPB) and the latter for benign prostatic hyperplasia (BPH), both are products of Merck & Co. There is 1 mg of finasteride in Propecia and 5 mg in Proscar. Merck's patent on finasteride for the treatment of BPH expired on June 19, 2006.^[23] Merck was awarded a separate patent for the use of finasteride to treat MPB. This patent is set to expire in November 2013.^[24]

Some studies have shown that the dose of finasteride needed to treat male pattern baldness may be smaller than 1 mg.^[25] Petitions to the FDA to re-examine the approved dosage in light of the statistical evidence and possible long-term risks,^[26] were met with the response that a study had shown increased effect of a 1 mg dose compared to 0.2 mg without added risks; the same study also concluded that doses of 0.01 mg per day were found to be ineffective in treating hair loss.^[26]

Chemical synthesis

Finasteride is synthesized from progesterone: ^{[27] [28]}

History

In 1974, Julianne Imperato-McGinley of Cornell Medical College in New York attended a conference on birth defects. She reported on a group of hermaphroditic children in the Caribbean who appeared sexually ambiguous at birth, and were initially raised as girls, but then grew external male genitalia and other masculine characteristic post-onset of puberty. Her research group found that these children shared a genetic mutation, causing deficiency of the 5-alpha reductase enzyme and male hormone dihydrotestosterone (DHT), which was found to have been the etiology behind abnormalities in male sexual development. Upon maturation, these individuals were observed to have smaller prostates which were underdeveloped, and were also observed to lack incidence of male pattern baldness.^[29][30]

In 1975, copies of Imperato-McGinley's presentation were seen by P. Roy Vagelos, who was then serving as Merck's basic-research chief. He was intrigued by the notion that decreased levels of DHT led to the development of smaller prostates. Dr. Vagelos then sought to create a drug which could mimic the condition found in the pseudo-hermaphroditic children in order to treat older men who were suffering from benign prostatic hyperplasia.^[31]

In 1992, finasteride (5 mg) was approved by the U.S. Food and Drug Administration (FDA) for treatment of benign prostatic hyperplasia (BPH), which Merck marketed under the brand name Proscar.

In 1997, Merck was successful in obtaining FDA approval for a second indication of finasteride (1 mg) for treatment of male pattern baldness (MPB), which was marketed under the brand name Propecia.

See also

• Dutasteride, related 5-alpha reductase inhibitor.

References

External links

• Proscar | Official website
• Propecia | Official website