Class: 5-alpha-Reductase Inhibitors
VA Class: HS900
Chemical Name: (5α,17β)-N-(1,1-dimethylethyl)-3-oxo-4-azaandrost-1-ene-17-carboxamide
CAS Number: 98319-26-7
Brands: Propecia, Proscar
Medically reviewed on February 2, 2018
Uses for Finasteride
Benign Prostatic Hypertrophy (BPH)
Treatment of symptomatic BPH to improve symptoms and reduce the risk of acute urinary retention and the need for surgery.1 8 15 16 17 19 Ineffective in patients who do not have evidence of prostatic enlargement.25
Used alone or in combination with an α1-adrenergic blocking agent (e.g., doxazosin).1 20 25 Combination therapy with a 5α-reductase inhibitor and an α1-blocker has been more effective than therapy with either drug alone in preventing long-term BPH symptom progression.1 20 25 Men at risk for BPH progression are most likely to benefit from combination therapy.20 25
Steroid 5α-reductase inhibitors may be a useful alternative to surgery in patients with obstructive manifestations who are awaiting or unwilling to undergo surgical correction of BPH; may aid those who are at increased risk from or are not candidates for prostate surgery.3 14 25 Also may be considered in patients who have symptomatic prostatic enlargement but whose symptoms are not bothersome (i.e., do not interfere with activities of daily living) in order to prevent progression of the disease.25
Although drug therapy usually is not as effective as surgical therapy, it may provide adequate symptomatic relief with fewer and less serious adverse effects compared with surgery.25
Effective in promoting hair regrowth in young and middle-aged men (18–41 years of age) with mild to moderate androgenetic alopecia and hair loss on the vertex of the scalp and/or anterior mid-scalp area; the effects on bitemporal recession are not established.d
Withdrawal of the drug leads to reversal of clinical benefit within 1 year.d Therapy must be continued to sustain initial regrowth and subsequent slowing of hair loss.d Maximum improvement in hair count occurs during first 2 years of therapy.d
Finasteride Dosage and Administration
5 mg once daily, alone or in combination with doxazosin mesylate.1
1 mg once daily.d
Continued use recommended to sustain benefit, which should be re-evaluated periodically.d
Discontinuance leads to reversal of effect within 12 months.d
Cautions for Finasteride
May cause fetal harm; teratogenicity demonstrated in animals.1
Animal studies indicate adverse effects on embryofetal development of male fetuses exposed to the drug during pregnancy (e.g., abnormalities of the external genitalia, decreased prostatic and seminal vesicular weights, delayed preputial separation, transient nipple development).1
No abnormalities were observed in female offspring exposed to any finasteride dosage in utero.1
Because of the potential for absorption through the skin and the subsequent potential risk to a male fetus, pregnant women or women who potentially may be pregnant should avoid direct contact with broken (e.g., crushed) tablets of the drug.1 21 d If such contact occurs, wash affected area immediately with soap and water.1 21
If used during pregnancy or if pregnancy occurs, apprise the pregnant woman of potential fetal hazard to the male fetus.1
Evaluate candidates for finasteride therapy for other urologic conditions that might mimic BPH, such as infection, prostate cancer, stricture disease, hypotonic bladder, other neurogenic disorders.1
Perform digital rectal examinations, as well as other screening tests for prostate cancer (e.g., serum prostate-specific antigen [PSA] concentration), before initiating therapy for BPH and periodically thereafter.1 27 28 29 (See Prostate-specific Antigen under Cautions and also see Specific Drugs and Laboratory Tests under Interactions.)
High-grade Prostate Cancer
In 2 placebo-controlled trials evaluating finasteride (5 mg daily for 7 years) or dutasteride (0.5 mg daily for 4 years) for prevention of prostate cancer, overall occurrence of prostate cancer was reduced (due to reduction in lower-grade tumors) but incidence of high-grade tumors (Gleason score 8–10) was increased in men receiving finasteride or dutasteride.1 22 29 d Not known whether detection bias (e.g., drug-induced reduction in prostate volume might have aided biopsy detection) or study-related factors influenced results.1 30 31
Breast cancer reported in several men receiving finasteride 5 mg daily (alone or in combination with doxazosin) and several placebo recipients in long-term trials of finasteride.1 19 20 d Also reported during postmarketing experience in men receiving finasteride 1 mg daily.d Not known whether a causal relationship exists between long-term finasteride use and breast neoplasia in men.1 d
No substantial differences in safety and efficacy for treatment of BPH in men ≥65 or ≥75 years of age relative to younger men.1 Efficacy for promoting hair regrowth in geriatric men with androgenetic alopecia not established.d
Common Adverse Effects
Interactions for Finasteride
Specific Drugs and Laboratory Tests
Drug or Test
Test for PSA
PSA decreased from 0.7 ng/mL at baseline to 0.5 ng/mL at 12 months with 1-mg daily dosage for androgenetic alopeciad
No substantial change in ratio of free to total PSA (percentage of free PSA)1
Take decrease into account for interpretation of PSA values in men receiving finasterided
For clinical interpretation of PSA values in men with BPH receiving finasteride 5 mg daily for ≥6 months, double the reported PSA value for comparison with normal values in men not receiving the drug1
No adjustment of reported values of ratio appears to be required1
Rapid, with maximum decrease in serum DHT concentrations at 8 hours following oral administration of first dose of 5 mg, and 65% suppression of serum DHT within 24 hours after oral administration of 1 mg.1 d
DHT suppression maintained throughout 24-hour dosage interval; DHT decreased by about 70% with 5-mg daily dosage for at least 4 years.1
Distributed into semen in amounts estimated to be 50- to 100-fold less than the dose (5 mcg) that had no effect on circulating DHT concentrations in men.1
Plasma Protein Binding
In patients with chronic renal impairment (Clcr 9–55 mL/minute), pharmacokinetics after single-dose administration appear to be similar to those in healthy individuals except that the proportion excreted in feces versus urine is increased in those with impairment.1
5-mg tablets: Tight, light resistant containers at room temperature <30°.1
1-mg tablets: Tight, light resistant containers at 15–30°C.d
Type 2 steroid 5α-reductase isoenzyme converts testosterone to DHT in the prostate gland, seminal vesicles, epididymides, liver, and the inner root sheath of hair follicles and is responsible for the formation of about two-thirds of circulating DHT.d g k l m n o
In men with androgenetic alopecia, decreases scalp DHT concentrations to levels found in hairy scalp, reduces serum DHT, increases hair regrowth, and slows hair loss.d g k l m o However, exact mechanism of action not fully elucidated.g l
Advice to Patients
Importance of informing patients that finasteride decreases serum PSA concentrations.1 21 r Importance of appropriate medical evaluation of any increase in PSA concentration.1 21 r If a PSA test is performed, importance of patient informing the clinician that he is taking a 5α-reductase inhibitor.1 21 r
Importance of informing patients that the incidence of high-grade prostate cancer was increased in men receiving 5α-reductase inhibitors (including finasteride) in clinical trials evaluating efficacy of these drugs for prostate cancer prevention.1
Risk to male fetuses.1 21 d r Importance of advising patients that pregnant women or women who may be pregnant should avoid direct contact with broken or crushed tablets of the drug; if such contact occurs, wash affected area immediately with soap and water and inform clinician.1 21 d f r (See Fetal/Neonatal Morbidity under Cautions.)
Advise that ≥6 months of continuous therapy may be required before improvement in BPH symptoms occurs and a decrease in prostate size may not noticeably improve urine flow or symptoms.21
Advise that ≥3 months of continuous therapy may be required before improvement in androgenetic baldness occurs, and if no improvement is observed after 12 months, further treatment is unlikely to be of benefit.r
Advise that hair growth gained during treatment for androgenetic baldness will likely be lost within 12 months after discontinuing the drug.r
Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.
Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.
* available from one or more manufacturer, distributor, and/or repackager by generic (nonproprietary) name
Propecia (available in regular and Pro-Pak)
AHFS DI Essentials. © Copyright 2018, Selected Revisions February 2, 2012. American Society of Health-System Pharmacists, Inc., 4500 East-West Highway, Suite 900, Bethesda, Maryland 20814.
1. Merck & Co, Inc. Proscar (finasteride) tablets prescribing information. Whitehouse Station, NJ; 2011 Jun.
2. Stoner E. The clinical development of a 5α-reductase inhibitor, finasteride. J Steroid Biochem Mol Biol. 1990; 37:375-8. http://www.ncbi.nlm.nih.gov/pubmed/1701660?dopt=AbstractPlus
3. Gormley GJ, Stoner E. The role of 5α-reductase inhibitors in the treatment of benign prostatic hyperplasia. Probl Urol. 1991; 5:436-40.
4. Catalone WJ, Smith DS, Ratliff TL et al. Measurement of prostate-specific antigen in serum as a screening test for prostate cancer. N Engl J Med. 1991; 324:1156-61. http://www.ncbi.nlm.nih.gov/pubmed/1707140?dopt=AbstractPlus
5. Stoner E. The clinical effects of a 5 alpha reductase inhibitor, finasteride, on benign prostatic hyperplasia. J Urol. 1992; 147:1298-302. http://www.ncbi.nlm.nih.gov/pubmed/1373779?dopt=AbstractPlus
6. De Schepper PJ, Imperato-McGinley J, Van Hecken A et al. Hormonal effects, tolerability, and preliminary kinetics in men of MK-906, a 5 alpha reductase inhibitor. Steroids. 1991; 56:469-71. http://www.ncbi.nlm.nih.gov/pubmed/1666698?dopt=AbstractPlus
7. McConnell JD, Wilson JD, George FW et al. Finasteride, an inhibitor of 5 alpha-reductase, suppresses prostatic dihydrotestosterone in men with benign prostatic hyperplasia. J Clin Endocrinol Metab. 1992; 74:505-8. http://www.ncbi.nlm.nih.gov/pubmed/1371291?dopt=AbstractPlus
8. The MK-906 (Finasteride) Study Group. One-year experience in the treatment of benign prostatic hyperplasia with finasteride. J Androl. 1991; 12:372-5. http://www.ncbi.nlm.nih.gov/pubmed/1722792?dopt=AbstractPlus
9. Vermeulen A, Giagulli VA, De Schepper P et al. Hormonal effects of a 5 alpha-reductase inhibitor (finasteride) on hormonal levels in normal men and in patients with benign prostatic hyperplasia. Eur Urol. 1991; 20(Suppl 1):82-6. http://www.ncbi.nlm.nih.gov/pubmed/1722168?dopt=AbstractPlus
10. Gormley GJ, Stoner E, Rittmaster RS et al. Effects of finasteride (MK-906), a 5 alpha-reductase inhibitor, on circulating androgens in male volunteers. J Clin Endocrinol Metab. 1990; 70:1136-41. http://www.ncbi.nlm.nih.gov/pubmed/2156887?dopt=AbstractPlus
11. Rittmaster RS, Stoner E, Thompson DL et al. Effect of MK-906, a specific 5 alpha-reductase inhibitor, on serum androgens and androgen conjugates in normal men. J Androl. 1989; 10:259-62. http://www.ncbi.nlm.nih.gov/pubmed/2550402?dopt=AbstractPlus
12. Geller J. Effect of finasteride, a 5 alpha-reductase inhibitor on prostate tissue androgens and prostate-specific antigen. J Clin Endocrinol Metab. 1990; 71:1552-5. http://www.ncbi.nlm.nih.gov/pubmed/1699965?dopt=AbstractPlus
13. Vermeulen A, Giagulli VA, De Schepper P et al. Hormonal effects of an orally active 4-azasteroid inhibitor of 5 alpha-reductase in humans. Prostate. 1989; 14:45-53. http://www.ncbi.nlm.nih.gov/pubmed/2538808?dopt=AbstractPlus
14. Chapple C. Medical treatment for benign prostatic hyperplasia. BMJ. 1992; 304:1198-9. http://www.ncbi.nlm.nih.gov/pubmed/1381250?dopt=AbstractPlus http://www.pubmedcentral.nih.gov/picrender.fcgi?tool=pmcentrez&artid=1881763&blobtype=pdf
15. Gormley GJ, Stoner E, Bruskewitz RC et al. The effect of finasteride in men with benign prostatic hyperplasia. N Engl J Med. 1992; 327:1185-91. http://www.ncbi.nlm.nih.gov/pubmed/1383816?dopt=AbstractPlus
16. Steiner JF. Finasteride: a 5α-reductase inhibitor. Clin Pharm. 1993; 12:15-23. http://www.ncbi.nlm.nih.gov/pubmed/7679063?dopt=AbstractPlus
17. Peters DH, Sorkin EM. Finasteride: a review of its potential in the treatment of benign prostatic hyperplasia. Drugs. 1993; 46:177-208. http://www.ncbi.nlm.nih.gov/pubmed/7691505?dopt=AbstractPlus
18. Merck Sharpe & Dohme. Proscar (finasteride) tablets prescribing information. West Point, PA; 1992 Sep.
19. McConnell JD, Bruskewitz R, Walsh P et al. The effect of finasteride on the risk of acute urinary retention and the need for surgical treatment among men with benign prostatic hyperplasia. N Engl J Med. 1998; 338:557-63. http://www.ncbi.nlm.nih.gov/pubmed/9475762?dopt=AbstractPlus
20. McConnell JD, Roehrborn CG, Bautista OM et al. The long-term effect of doxazosin, finasteride, and combination therapy on the clinical progression of benign prostatic hyperplasia. N Engl J Med. 2003; 349:2387-98. http://www.ncbi.nlm.nih.gov/pubmed/14681504?dopt=AbstractPlus
21. Merck & Co, Inc. Patient information about Proscar (finasteride). Whitehouse Station NJ; 2011 Jun.
22. Thompson IM, Goodman PJ, Tangen CM et al. The influence of finasteride on the development of prostate cancer. N Engl J Med 2003; 349:215-24.. http://www.ncbi.nlm.nih.gov/pubmed/12824459?dopt=AbstractPlus
23. Prostate cancer. From: PDQ. Physician data query (database). Bethesda, MD: National Cancer Institute; 2006 Jul 21.
24. Scardino PT. The prevention of prostate cancer—the dilemma continues. N Engl J Med 2003; 349:297-9. http://www.ncbi.nlm.nih.gov/pubmed/12824458?dopt=AbstractPlus
25. American Urological Association. Guideline on the management of benign prostatic hyperplasia (BPH)(2003/updated 2006). Available at: http://www.auanet.org. Accessed 2006 Aug 10.
26. Vaughan ED. Medical management of benign prostatic hyperplasia—are two drugs better than one? N Engl J Med. 2003; 349:2440-51. Editorial.
27. de la Rossette JJ, Alivizatos G, Madersbacher S et al. EAU guidelines on benign prostatic hyperplasia (BPH). Eur Urol. 2001; 40:256-63. http://www.ncbi.nlm.nih.gov/pubmed/11684840?dopt=AbstractPlus
28. Agency for Health Care Policy and Research. Benign prostatic hyperplasia: diagnosis and treatment. J Am Geriatric Soc. 1998; 46:1163-5.
29. Food and Drug Administration. FDA drug safety communication: 5-alpha reductase inhibitors (5-ARIs) may increase the risk of a more serious form of prostate cancer. Rockville, MD; 2011 Jun 9. From FDA website. http://www.fda.gov/Drugs/DrugSafety/ucm258314.htm
30. Theoret MR, Ning YM, Zhang JJ et al. The risks and benefits of 5α-reductase inhibitors for prostate-cancer prevention. N Engl J Med. 2011; 365:97-9. http://www.ncbi.nlm.nih.gov/pubmed/21675880?dopt=AbstractPlus
31. Lucia MS, Epstein JI, Goodman PJ et al. Finasteride and high-grade prostate cancer in the Prostate Cancer Prevention Trial. J Natl Cancer Inst. 2007; 99:1375-83. http://www.ncbi.nlm.nih.gov/pubmed/17848673?dopt=AbstractPlus
a. AHFS drug information 2005. McEvoy GK, ed. Finasteride. Bethesda, MD: American Society of Health-System Pharmacists; 2005:3561-2.
b. AHFS drug information 2005. McEvoy GK, ed. Finasteride. Bethesda, MD: American Society of Health-System Pharmacists; 2005:3472-3.
d. Merck & Co. Propecia (finasteride) tablets prescribing information. Whitehouse Station, NJ; 2011 Jun.
f. Anon. Propecia and Rogaine Extra Strength for alopecia. Med Lett Drugs Ther. 1998; 40:25-7. http://www.ncbi.nlm.nih.gov/pubmed/9505960?dopt=AbstractPlus
g. Dallob AL, Sadick NS, Unger W. The effect of finasteride, a 5α-reductase inhibitor, on scalp skin testosterone and dihydrotestosterone concentrations in patients with male pattern baldness. J Clin Endocrinol Metab. 1994; 79:703-6. http://www.ncbi.nlm.nih.gov/pubmed/8077349?dopt=AbstractPlus
h. Stoner E. The clinical development of a 5α-reductase inhibitor, finasteride. J Steroid Biochem Mol Biol. 1990; 37:375-8. http://www.ncbi.nlm.nih.gov/pubmed/1701660?dopt=AbstractPlus
i. Gormley GJ, Stoner E, Rittmaster RS et al. Effects of finasteride (MK-906), a 5 α- reductase inhibitor, on circulating androgens in male volunteers. J Clin Endocrinol Metab. 1990; 70:1136-41. http://www.ncbi.nlm.nih.gov/pubmed/2156887?dopt=AbstractPlus
j. Rittmaster RS, Stoner E, Thompson DL et al. Effect of MK-906, a specific 5 alpha- reductase inhibitor, on serum androgens and androgen conjugates in normal men. J Androl. 1989; 10:259-62. http://www.ncbi.nlm.nih.gov/pubmed/2550402?dopt=AbstractPlus
k. Rittmaster RS. Finasteride. New Engl J Med. 1994; 330:120-5. http://www.ncbi.nlm.nih.gov/pubmed/7505051?dopt=AbstractPlus
l. Walsh DS, Dunn CL, James WD. Improvement in androgenetic alopecia (stageV) using topical minoxidil in a retinoid vehicle and oral finasteride. Arch Dermatol. 1995; 131:1373-5. http://www.ncbi.nlm.nih.gov/pubmed/7492124?dopt=AbstractPlus
m. Chen W, Zouboulis CC, Orfanos CE. The 5α-reductase system and its inhibitors: recent development and its perspective in treating androgen-dependent skin disorders. Dermatology. 1996; 193:177-84. http://www.ncbi.nlm.nih.gov/pubmed/8944337?dopt=AbstractPlus
n. Gormley GJ. Finasteride: a clinical review. Biomed Pharmacother. 1995; 49:319-24. http://www.ncbi.nlm.nih.gov/pubmed/8562856?dopt=AbstractPlus
o. Amichai B, Grunwald MH, Sobel R. 5α-reductase inhibitors—a new hope in dermatology. Int J Dermatol. 1997; 36:182-4. http://www.ncbi.nlm.nih.gov/pubmed/9158996?dopt=AbstractPlus
p. Drake LA, Dinehart SM, Farmer ER et al for the American Academy of Dermatology. Guidelines of care for andogenetic alopecia. J Am Acad Dermatol. 1996; 35:465-8. http://www.ncbi.nlm.nih.gov/pubmed/8784287?dopt=AbstractPlus
r. Merck & Co. Propecia (finasteride) patient information. Whitehouse Station, NJ; 2011 Jun.
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