Author: Dr Nicholas M Birchall, Dermatologist, Auckland, New Zealand, 1998.
Male pattern hair loss, or androgenetic alopecia, is an androgen-dependent disorder. In genetically susceptible men, dihydrotestosterone (DHT), a potent metabolite of the male androgen testosterone, contributes to male pattern hair loss. The conversion of testosterone to DHT is regulated by the enzyme 5-alpha reductase.
Finasteride (Propecia® and others) is a specific type II 5-alpha reductase inhibitor. That is, it inhibits the enzyme responsible for regulating the conversion of testosterone to dihydrotestosterone (DHT). By reducing DHT levels in the scalp, the drug decreases DHT's effects on the hair follicles, reversing the process of hair loss.
Finasteride is indicated for the treatment of men with male pattern hair loss (androgenetic alopecia) to prevent further hair loss and increase hair growth.
Finasteride inhibits expression of the enzyme, 5-alpha reductase, which regulates the production of dihydrotestosterone (DHT). By lowering DHT levels in the scalp, it reduces DHT's harmful effect on hair follicles. Finasteride decreases DHT concentrations in the serum and the scalp by up to 70 and 60%, respectively.
Finasteride is an oral pill to be taken once a day. The usual dose is 1mg daily taken with or without food, at any time during the day.
A topical formulation of finasteride has been approved in India and has been found to be as effective as oral finasteride.
Finasteride is not indicated for use in women with hair loss (female pattern hair loss) but is occasionally used (off-label) postmenopause. Finasteride is contraindicated in women when they are or may potentially be pregnant, because it may cause abnormalities of the external genitalia of a male fetus (Pregnancy Category X, i.e., drugs that have such a high risk of causing permanent damage to the fetus that they should not be used in pregnancy or when there is a possibility of pregnancy.)
The data are from three large, multicentre, placebo-controlled studies of 1,879 men with mild-to-moderate, but not complete, male pattern hair loss. The men received either oral finasteride once daily or placebo for one year. The endpoints for the studies were objective hair counts taken from a 1-inch diameter circular area, and subjective assessments of improvement by patients, investigators, and an independent panel of dermatology experts who evaluated pre- and post-treatment photographs.
The trials showed that finasteride can prevent hair loss in men with mild-to-moderate male pattern hair loss. In two of the clinical studies involving men with mild-to-moderate male pattern hair loss, 86% of men treated with finasteride maintained or showed an increase in the amount of their hair based on hair counts during the course of the studies. Only 14% of men treated with finasteride had further hair loss after 12 months of treatment, compared with 58% of placebo patients.
On-going studies have demonstrated that finasteride halts hair loss or regrows hair in 9 out of 10 men taking it longterm every day.
It is difficult to predict which patients will respond and to what extent. Patients studied in clinical trials had mild-to-moderate, but not complete, hair loss, and ranged in age from 18 to 41.
Daily use for three months or more may be necessary before a patient will notice the prevention of further hair loss or increased hair growth.
No clinical data exist for completely bald men.
No clinical trials have been conducted in men over the age of 41 to treat male pattern hair loss with finasteride.
Daily use of finasteride for three months or more may be necessary before a patient will notice the prevention of further hair loss or increased hair growth. There are no controlled clinical data on treatment for longer than 12 months. It probably will be necessary to continue treatment indefinitely to maintain the benefits.
If a patient stops taking finasteride, DHT levels will rise again in the scalp, and it is likely that hair loss will resume.
Finasteride is a specific inhibitor of type II 5-alpha reductase, which is found primarily in scalp hair follicles. In clinical trials, there was no reported effect on the hair on the other parts of the body.
Women who are or may potentially be pregnant must not use finasteride since it may cause a specific birth defect in a male fetus (hypospadias).
In clinical trials, finasteride was very well tolerated in men, with most patients reporting no serious side effects. The principal side effects associated with finasteride were decreased libido (1.8% of finasteride patients versus 1.3% on placebo) and erectile dysfunction (1.3% finasteride versus 0.7% placebo). In addition, decreased volume of ejaculate was reported in 0.8% of men treated with finasteride and 0.4% of those on placebo. Gynaecomastia (breast enlargement) has also been reported. All of these side effects resolved upon discontinuation of therapy, and also resolved in many men who preferred to continue therapy. Postmarketing reports have included some patients complaining of depression, but the risk of this is likely very small.
Finasteride was evaluated in 3,200 men and it was very well tolerated, including patients on therapy for up to two years. Long-term suppression of DHT does not appear to be harmful. This is based on extensive research, dating back to 1974, of men born with a deficiency of 5-alpha reductase.
Finasteride results in an average reduction of 50% for the prostate specific antigen score (PSA test). The score should be doubled to work out the risk of prostate cancer. The risk of prostate cancer related to finasteride use has been very carefully reviewed. Current evidence is reassuring and it does not seem to increase the risk or cancer nor result in more serious disease than in those that do not take the drug. Although some cases of breast cancer have been reported in patients on finasteride, there is no evidence that the drug was the cause.
Update (2017). Finasteride can occasionally result in erectile dysfunction during treatment. Persistent erectile dysfunction lasting more than 3 months has been reported in about 1% of men taking low-dose finasteride for more than 205 days who had discontinued the treatment. Other symptoms rarely reported include depression, suicidal ideation, anxiety, panic attacks, Peyronie disease, penile shrinkage, gynaecomastia, muscle atrophy, cognitive impairment, insomnia, severely dry skin and tinnitus. However, these persistent side effects have been noted at similar rates in clinical trials in patients taking placebo medications. Causative association is uncertain.
Finasteride is not indicated for use in women or children. However, it is sometimes prescribed off-label for postmenopausal women without problems. Finasteride is contraindicated in women who are or may potentially be pregnant. Finasteride is contraindicated in patients who are hypersensitive to any component of the product.
It is not recommended in men that are subfertile. In men planning to have children, some doctors check sperm counts prior to starting finasteride and repeat it after 6 months of treatment. If the sperm count has reduced, finasteride should be stopped.
No drug interactions of clinical importance have been identified. Studies have been conducted with finasteride and antipyrine, digoxin, glyburide, propranolol, theophylline, and warfarin, and no interactions were found. In clinical trials, finasteride was used concomitantly with ACE inhibitors, acetaminophen, alpha blockers, benzodiazepines, beta blockers, calcium channel blockers, cardiac nitrates, diuretics, H2 antagonists, HMG-CoA Reductase inhibitors, prostaglandin synthesase inhibitors (NSAIDs), and quinolones, without evidence of clinically significant adverse interactions.
There are no human data supporting the use of the combination of finasteride and minoxidil. Scientific studies would be required to assess the safety and efficacy of such a combination.
However, the combination has been safely prescribed to many patients and has appeared useful. If switching from one treatment to the other, it is best to overlap by six months to reduce the chance of hair loss from the withdrawal of the first treatment while waiting for a response to the new product.
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