The 5α-reductase inhibitor finasteride blocks the conversion of testosterone to dihydrotestosterone (DHT), the androgen responsible for male pattern hair loss (androgenetic alopecia) in genetically predisposed men.
Results of phase III clinical studies in 1879 men have shown that oral finasteride 1 mg/day promotes hair growth and prevents further hair loss in a significant proportion of men with male pattern hair loss. Evidence suggests that the improvement in hair count reported after 1 year is maintained during 2 years’ treatment. In men with vertex hair loss, global photographs showed improvement in hair growth in 48% of finasteride recipients at 1 year and in 66% at 2 years compared with 7% of placebo recipients at each time point. Furthermore, hair counts in these men showed that 83% of finasteride versus 28% of placebo recipients had no further hair loss compared with baseline after 2 years.
The clinical efficacy of oral finasteride has not yet been compared with that of topical minoxidil, the only other drug used clinically in patients with male pattern hair loss.
Therapeutic dosages of finasteride are generally well tolerated. In phase III studies, 7.7% of patients receiving finasteride 1 mg/day compared with 7.0% of those receiving placebo reported treatment-related adverse events. The overall incidence of sexual function disorders, comprising decreased libido, ejaculation disorder and erectile dysfunction, was significantly greater in finasteride than placebo recipients (3.8 vs 2.1%). All sexual adverse events were reversed on discontinuation of therapy and many resolved in patients who continued therapy. No other drug-related events were reported with an incidence ≥1% in patients receiving finasteride. Most events were of mild to moderate severity. Oral finasteride is contraindicated in pregnant women because of the risk of hypospadias in male fetuses.
Conclusions:Oral finasteride promotes scalp hair growth and prevents further hair loss in a significant proportion of men with male pattern hair loss. With its generally good tolerability profile, finasteride is a new approach to the management of this condition, for which treatment options are few. Its role relative to topical minoxidil has yet to be determined.
Finasteride specifically inhibits the type II 5α-reductase enzyme which converts testosterone to dihydrotestosterone (DHT), the androgen responsible for the development of male pattern hair loss in genetically predisposed men. Oral finasteride 1 mg/day significantly reduced serum DHT levels by a median 68.4% in men with male pattern hair loss treated for 1 year. A corresponding 9.1% (median) increase in testosterone levels from baseline was reported, but these levels remained within the normal physiological range.
Oral finasteride 0.2 to 5 mg/day for 4 to 6 weeks reduced DHT levels by up to 65% in the scalp, the desired site of action of finasteride in men with male pattern hair loss.
Finasteride did not affect serum luteinising hormone or follicle-stimulating hormone responses to gonadotropin-releasing hormone stimulation in healthy volunteers, and therefore does not appear to influence the hypothalamic-pituitary-testicular axis. In addition, the drug did not alter serum prolactin, sex hormone-binding globulin, aldosterone or cortisol levels in healthy volunteers. Slight increases in serum estradiol levels were seen but, like testosterone levels, these remained within the normal physiological range and the ratio of testosterone to estradiol was unaltered.
Finasteride 1 mg/day does not appear to significantly affect ejaculate volume or other measures of testosterone-mediated semen production such as sperm motility, morphology and number. In addition, this dosage of finasteride had no clinically significant effects on prostate volume in healthy men aged ≤41 years, but caused a slight reduction in serum prostate-specific antigen levels. Evidence suggests that finasteride has no adverse effects on lipid or bone metabolism.
Peak plasma concentrations of finasteride (9.2 µg/L) were reached 1 to 2 hours after drug administration in healthy volunteers who received a 1 mg/day dosage of finasteride for 17 days. Modest accumulation of finasteride in plasma was reported with repeated administration, but trough concentrations appeared to reach steady state within 3 days.
The oral bioavailability of finasteride (80%) is not affected by the presence of food.
Finasteride undergoes wide tissue distribution (volume of distribution = 76L), with ≈90% of circulating finasteride being protein bound. The drug has been detected in nanogram quantities in seminal fluid but these low levels have no clinical significance.
After oral administration, finasteride is extensively metabolised in the liver to compounds which are then eliminated in the bile (56.8%) and the urine (39.1%). Virtually no unchanged drug is recovered after an oral dose of finasteride. The mean terminal elimination half-life of finasteride 1 mg/day after repeated administration is 4.8 hours.
The elimination of finasteride is slower in elderly (≥70 years) than in younger (45 to 60 years) volunteers, but no dosage adjustment is warranted in the former age group, nor in patients with renal impairment. Reduced renal excretion of finasteride is compensated for by an increase in faecal elimination. There are currently no data on the pharmacokinetic properties of finasteride in patients with hepatic impairment.
Although finasteride is principally metabolised by cytochrome P450 3A4 enzymes within the liver, no clinically significant interactions have been reported between finasteride and digoxin, propranolol, aminophylline, warfarin, glibenclamide (glyburide) or antipyrine.
Oral finasteride 1 mg/day has shown efficacy in men with male pattern hair loss. The clinical use of this dosage of finasteride has been assessed in 3 phase III studies involving 1879 men with vertex or frontal hair loss who were treated for up to 2 years. Finasteride produced statistically significant increases in scalp hair growth from baseline within several months of starting treatment, a finding documented by hair count, patient self-assessment, investigator assessment and pre- and post-treatment clinical assessment based on standardised photos. Importantly, finasteride prevented the further hair loss seen in placebo recipients. In men with vertex hair loss, the mean improvement in hair count reported after 1 year with finasteride was maintained during a further 12 months’ treatment. Global photographs of the vertex area showed improvement in hair growth in 48% of finasteride recipients at 1 year (versus 7% with placebo) and in 66% at 2 years (versus 7% with placebo). Furthermore, vertex hair counts showed that 83% of finasteride versus 28% of placebo recipients had no further hair loss compared with baseline after 2 years. Hair growth was enhanced in patients who switched from placebo to finasteride after 12 months but declined progressively in those switched from finasteride to placebo.
Available data from 1879 patients with male pattern hair loss who received either finasteride 1 mg/day or placebo for 1 year in phase III studies show that finasteride is generally well tolerated. Overall, 7.7% of finasteride and 7.0% of placebo recipients reported mild to moderate treatment-related adverse events (1.4 and 1.6% withdrew). The only events reported more frequently in finasteride than placebo recipients were sexual disorders (3.8 vs 2.1%; p = 0.041), which comprised decreased libido (1.8 vs 1.3%), ejaculation disorders (1.2 vs 0.7%) and erectile dysfunction (1.3 vs 0.7%). These resolved in many men who reported them but remained on therapy and in all men who discontinued therapy because of these adverse events. No other drug-related events were reported with an incidence ≥1% in finasteride recipients.
The incidence of drug-related laboratory events was similar in finasteride and placebo groups (2.6 vs 2.4%). Finasteride had no significant effects on non-scalp body hair.
Dosage and Administration
Finasteride is indicated for the treatment of men with male pattern hair loss. The recommended dosage of finasteride in male pattern hair loss is 1 mg/day, taken with or without food. Daily treatment for 3 months or more is necessary before results are seen, and continued treatment is essential to sustain benefit. Furthermore, the effects of the drug are reversed within 12 months after treatment cessation.
There are no current data to support the use of finasteride in women with androgenetic alopecia. Moreover, pregnant women should not be directly exposed to finasteride by using or handling crushed tablets because of the risk of hypospadias developing in a male fetus.
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Various sections of the manuscript reviewed by: W.F. Bergfeld, Department of Dermatology, Cleveland Clinic Foundation, Cleveland, Ohio, USA; R.P.R. Dawber, Dermatology Department, Oxford Radcliffe Hospital, Oxford, England; R. Hoffmann, Department of Dermatology, Philipp University, Marburg, Germany; F. Mazzarella, Department of Dermatology, University of Bari, Bari, Italy; E. Olsen, Division of Dermatology, Duke University Medical Center, Durham, North Carolina, USA; J.F. Steiner, School of Pharmacy, University of Wyoming, Laramie, Wyoming, USA; R.S. Rittmaster, Department of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada.
Sources: Medical literature published in any language since 1966 on finasteride, identified using AdisBase (a proprietary database of Adis International, Auckland, New Zealand), Medline and EMBASE. Additional references were identified from the reference lists of published articles. Bibliographical information, including contributory unpublished data, was also requested from the company developing the drug.
Search strategy: AdisBase search terms were ‘finasteride’ or ‘MK-906’ and ‘alopecia’. Medline and EMBASE search terms were ‘finasteride’. Searches were last updated 1 Nov 1998.
Selection: Studies in patients with male pattern baldness who received finasteride. Inclusion of studies was based mainly on the methods section of the trials. When available, large, well controlled trials with appropriate statistical methodology were preferred. Relevant pharmacodynamic and pharmacokinetic data are also included.
Index terms: finasteride, androgenetic alopecia, male pattern baldness, pharmacokinetics, pharmacodynamics, therapeutic use, tolerability, dosage and administration.
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McClellan, K.J., Markham, A. Finasteride. Drugs 57, 111–126 (1999). https://doi.org/10.2165/00003495-199957010-00014
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