Finasteride is a 5-alpha reductase inhibitor used to treat symptomatic benign prostatic hyperplasia (BPH), a condition found in the majority of men over the age of 50. Finasteride has been shown to increase and maintain maximum urine flow rate in men with BPH, although less than 50% of men show improvement despite a reduction in prostate size. In a typical patient undergoing treatment for BPH with finasteride (>= 6 months), a 50% decrease in serum PSA concentrations can be expected; however, individual patients may experience varying decreases in PSA values. During treatment, serum PSA concentrations may decrease even in the presence of prostate cancer. If clinicians use serum PSA concentrations as an aid in the detection of prostate cancer in men receiving finasteride, values should be doubled for comparison with normal ranges in untreated men. Any increase from baseline, even if the value is within the normal range for untreated men, may signal the presence of prostate cancer. If clinicians elect to use percent free PSA (free to total PSA ratio) as a marker, no adjustment in PSA values appear to be necessary as the value is not significantly decreased by finasteride. In June 2011, a review of two large, randomized controlled trials, the Prostate Cancer Prevention Trial (PCPT) and the Reduction by Dutasteride of Prostate Cancer Events (REDUCE) trial prompted the FDA to alert healthcare professionals of the potential risk of an increased incidence of high-grade prostate cancer in patients receiving finasteride or dutasteride treatment. Results from the PCPT trial showed that men receiving finasteride had a 26% decreased risk of being diagnosed with prostate cancer overall when compared to placebo (p < 0.0001); however, the risk reduction was limited to Gleason score (GS) <= 6 cancers. There was an increased incidence of GS 8-10 prostate cancers with finasteride compared to placebo (1.8% vs. 1.1%, respectively). Finasteride is also used for treating hair loss in men and has been shown to be effective for mild to moderate hair loss of the vertex and anterior mid-scalp area; efficacy in bitemporal recession has not been established. Finasteride (Proscar) was approved by the FDA in June 1992 for the treatment of BPH. Another finasteride oral dosage form, Propecia, was approved by the FDA in December 1997 for the treatment of male pattern baldness (i.e., androgenetic alopecia). Finasteride is also used investigationally as an alternative agent for treating hirsutism.
General Administration Information
For storage information, see the specific product information within the How Supplied section.
Hazardous Drugs Classification
-NIOSH 2016 List: Group 3
-NIOSH (Draft) 2020 List: Table 2
-Observe and exercise appropriate precautions for handling, preparation, administration, and disposal of hazardous drugs.
-Use gloves to handle. Cutting, crushing, or otherwise manipulating tablets will increase exposure and require additional protective equipment. Oral liquid drugs require double chemotherapy gloves and protective gown. Eye/face and respiratory protection may be needed during preparation and administration.
Route-Specific Administration
Oral Administration
-Finasteride may be administered without regard to meals.
-Women who are pregnant or may get pregnant must not handle/administer broken or crushed finasteride tablets; the active ingredient could harm the unborn baby. Exposure to whole tablets is not expected to cause harm as long as they are not swallowed.
In a long-term (4 years) clinical trial in men with benign prostatic hypertrophy (BPH), the most frequently reported adverse reactions to finasteride were related to sexual function and breast-related events. At 1 year, the adverse reactions reported to be drug-related were impotence (erectile dysfunction), libido decrease, decreased ejaculate volume, ejaculation dysfunction, breast enlargement, and breast tenderness (mastalgia). There was no significant difference between finasteride and placebo in the incidences of impotence, decreased libido, and ejaculation dysfunction in years 2 to 4 of the study. In controlled trials of finasteride for the treatment of male pattern hair loss, 1.4% of patients discontinued therapy due to adverse events; discontinuation of therapy because of a drug-related sexual adverse experience occurred in 1.2% of patients. The following adverse events were reported in finasteride-treated patients: libido decrease (1.8%), erectile dysfunction (impotence) (1.3%), and ejaculation disorder (1.2%), primarily decreased ejaculate volume. The incidence of each of the above adverse effects decreased to 0.3% or less by the fifth year of treatment. Gynecomastia has been the most frequently reported adverse effect with use of finasteride since the drug was marketed. Data indicate the onset of gynecomastia has ranged from 14 days to 2.5 years (median: 180 days) of treatment. Thirty percent had unilateral gynecomastia, 25% had bilateral involvement, and in other cases this information was not specified. Twenty-seven percent of patients were also taking other medications that are known to cause gynecomastia. Gynecomastia resolved either completely or partially in 80% of subjects after finasteride was discontinued; however, in at least 2 cases, a new primary malignancy of primary intraductal breast cancer subsequently developed. Male breast cancer has been reported during postmarketing experience. In one trial where patients were randomized to receive finasteride 5 mg/day, doxazosin 4 or 8 mg/day, a combination of the two drugs, or placebo, four patients reported breast cancer as an adverse experience; three of the patients were receiving finasteride therapy and one patient was receiving combination therapy. Other postmarketing adverse reactions reported with finasteride use have included decreased libido and libido disorders that continued after discontinuation of treatment, depression, suicidal ideation and behavior, hematospermia, testicular pain that continued after discontinuation of treatment, problems with ejaculation or erectile dysfunction that continued after stopping the medication, and orgasm dysfunction or other orgasm disorders.
Finasteride may cause poor sperm quality, including spermatogenesis inhibition or oligospermia, decreased sperm motility, or decreased semen volume. Consider the potential effects on semen when assessing a male with infertility who is receiving finasteride treatment. In a 52-week, randomized, double-blind, placebo-controlled study in healthy men, finasteride (5 mg PO once daily) significantly decreased total sperm count (-34.3%) compared to baseline at 26 weeks but not at 52 weeks or at the 24-week follow-up. Semen volume was decreased at 52 weeks for finasteride (-14.5%), but the effect was not statistically significant. Sperm concentration was decreased by finasteride (-7.4%) but was not significant for either drug. Significant reductions of 6% to 12% in sperm motility were observed during treatment. Sperm morphology was not affected. One subject taking finasteride had decreases in sperm count of more than 90% of baseline values at 52 weeks; partial recovery was noted at the 24-week follow-up. During postmarketing surveillance, male infertility and/or poor seminal quality following treatment discontinuation have been reported. Normalization or improvement of seminal quality has also been reported after discontinuation of finasteride.
During clinical trials, rash (unspecified) was reported in approximately 0.5% of patients receiving finasteride treatment. Hypersensitivity reactions have been reported with finasteride use postmarketing and have included rash, pruritus, urticaria, and angioedema (including swelling of the lips, tongue, throat, and face).
By inhibiting the conversion of testosterone to DHT, finasteride and other 5-alpha-reductase inhibitors have the ability to cause teratogenesis, specifically abnormalities in the external genitalia of the male fetus (e.g., hypospadias).
Finasteride is not FDA-approved for use in females of childbearing potential and is contraindicated during pregnancy. Finasteride may cause fetal harm. Finasteride and other 5-alpha-reductase inhibitors, by inhibiting the conversion of testosterone to 5-alpha-dihydrotestosterone (DHT), have the ability to cause abnormalities in the external genitalia of the male fetus if administered to pregnant females. Pregnant women or females trying to conceive should not handle crushed or broken finasteride tablets. The distribution of finasteride into human semen has been assessed and appears to be well below the threshold concentration associated with fetal anomalies in animals.
Finasteride is not FDA-approved for use in females of childbearing potential and is recommended to be avoided during breast-feeding. It is not known whether finasteride is excreted in human milk. Therefore, the effects of finasteride on breast-feeding or a nursing infant cannot be determined.
Finasteride is not indicated for use in adolescents, children, or infants. Safety and effectiveness have not been established in pediatric patients under 18 years of age.
Finasteride should be used with caution in patients with hepatic disease, since finasteride is metabolized extensively in the liver. Data are lacking regarding the incidence of adverse effects or drug accumulation in patients with hepatic impairment.
Finasteride reduces total serum prostate specific antigen (PSA). In a typical patient undergoing treatment for BPH with finasteride (>= 6 months), a 50% decrease in serum PSA concentrations can be expected; however, individual patients may experience varying decreases in PSA values. During treatment, serum PSA concentrations may decrease even in the presence of prostate cancer. If clinicians use serum PSA concentrations as an aid in the detection of prostate cancer in men receiving finasteride, values should be doubled for comparison with normal ranges in untreated men. Any increase from baseline, even if the value is within the normal range for untreated men, may signal the presence of prostate cancer. If clinicians elect to use percent free PSA (free to total PSA ratio) as a marker, no adjustment in PSA values appear to be necessary as the value is not significantly decreased by finasteride. In June 2011, a review of two large, randomized controlled trials, the Prostate Cancer Prevention Trial (PCPT) and the Reduction by Dutasteride of Prostate Cancer Events (REDUCE) trial prompted the FDA to alert healthcare professionals of the potential risk of an increased incidence of high-grade prostate cancer in patients receiving finasteride or dutasteride treatment. Results from the PCPT trial showed that men receiving finasteride had a 26% decreased risk of being diagnosed with prostate cancer when compared to placebo (p < 0.0001); however, the risk reduction was limited to Gleason score (GS) <= 6 cancers. There was an increased incidence of GS 8-10 prostate cancers with finasteride compared to placebo (1.8% vs. 1.1%, respectively). Therefore, in initiating or continuing treatment with finasteride, clinicians should weigh the known benefits of treatment against the potential risk and be aware that finasteride may increase the risk of high-grade prostate cancer. Further, lower urinary tract symptoms of BPH can be indicative of other urological diseases, including prostate cancer. Patients should be assessed to rule out other urological diseases prior to treatment with finasteride. Patients with a large residual urinary volume and/or severely diminished urinary flow may not be good candidates for 5-alpha-reductase inhibitor therapy and should be carefully monitored for urinary tract obstruction.
Men treated with finasteride should refrain from blood donation while taking finasteride. The purpose of this is to prevent administration of finasteride to a pregnant female transfusion recipient.
Clinical efficacy studies of finasteride for hair loss did not include subjects aged 65 and over. Based on the pharmacokinetics of finasteride 5 mg, no dosage adjustment is necessary in the geriatric patient. However, the efficacy of finasteride for hair loss in the elderly has not been established.
The clinical significance of the effect of finasteride on semen characteristics for an individual male patient's fertility is not known; consider the potential effects on semen when assessing a male with infertility. Finasteride may cause spermatogenesis inhibition or oligospermia, decreased sperm motility, or decreased semen volume. In a 52-week, randomized, double-blind, placebo-controlled study in healthy men, finasteride (5 mg PO once daily) significantly decreased total sperm count (-34.3%) compared to baseline at 26 weeks but not at 52 weeks or at the 24-week follow-up. Semen volume was decreased at 52 weeks for finasteride (-14.5%), but the effect was not statistically significant. Sperm concentration was decreased by finasteride (-7.4%) but was not significant for either drug. Significant reductions of 6% to 12% in sperm motility were observed during treatment. Sperm morphology was not affected. One subject taking finasteride had decreases in sperm count of more than 90% of baseline values at 52 weeks; partial recovery was noted at the 24-week follow-up. Other data obtained from the manufacturer showed 24 weeks of finasteride treatment to healthy male volunteers resulted in no clinically meaningful effects on sperm concentration, mobility, morphology, or pH; however, a median decrease in ejaculate volume of 0.6 mL (22.1%) with a concomitant reduction in total sperm per ejaculate was observed. These values remained within normal range and were reversible upon treatment discontinuation (average time to baseline volume, 84 weeks). During post marketing surveillance, male infertility and poor seminal quality following treatment discontinuation have been reported. It should be noted that normalization or improvement of seminal quality has also been reported after discontinuation of finasteride.
For the treatment of benign prostatic hyperplasia (BPH):
Oral dosage (e.g., Proscar and generic equivalents):
Adults: 5 mg PO once daily.
For the treatment of male pattern hair loss (i.e., androgenetic alopecia), in patients with mild to moderate hair loss of the vertex and anterior mid-scalp area:
Oral dosage (e.g., Propecia and generic equivalents):
Adult males: 1 mg PO once daily. Daily use for 3 months or more is necessary before benefit is observed. Continued use is recommended to sustain benefit. Withdrawal of treatment leads to reversal of effect within 12 months.
For the second-line treatment of hirsutism*:
Oral dosage:
Adult, non-pregnant women: 5 mg PO once daily either alone or in combination with oral contraceptives was shown to reduce hirsutism in women with mild hirsutism. Women with moderate to severe hirsutism either do not respond or only respond initially. Adverse effects from finasteride were minimal compared to other antiandrogens such as cyproterone, flutamide, and spironolactone.
For prostate cancer prophylaxis*:
Oral dosage:
Adults: The risks of finasteride for prostate cancer prevention outweigh the benefits. In a 7-year placebo-controlled study, finasteride 5 mg PO once daily was shown to prevent or delay the development of prostate cancer in healthy men (>= 55 years of age) with a low risk of prostate cancer (PSA <= 3 ng/mL). Prostate specific antigen (PSA) levels, digital rectal exams, and biopsies were used to aid in the diagnosis of prostate cancer. Results showed that men receiving finasteride had a 26% decreased risk of being diagnosed with prostate cancer compared to placebo (p < 0.0001); however, the risk reduction was limited to Gleason score (GS) <= 6 cancers. There was an increased incidence of high-grade prostate cancer (GS 7-10) with finasteride compared to placebo (6.4% vs. 5.2%, respectively, p = 0.005). Finasteride was also associated with a higher incidence of sexual side effects versus placebo.
Maximum Dosage Limits:
-Adults
Males: 5 mg/day PO for benign prostatic hyperplasia (BPH); the manufacturer literature states that patients have received up to 80 mg/day PO for three months without adverse effects; however, it is not clear if the dose was used therapeutically or provided additional benefit over the usual dose range. Maximum dose-response is 1 mg/day PO for alopecia.
-Elderly
Males: 5 mg/day PO for benign prostatic hyperplasia (BPH); the manufacturer literature states that patients have received up to 80 mg/day PO for three months without adverse effects; however, it is not clear if the dose was used therapeutically or provided additional benefit over the usual dose range. Maximum dose-response is 1 mg/day PO for alopecia.
-Adolescents
Not indicated.
-Children
Not indicated.
Patients with Hepatic Impairment Dosing
Finasteride should be initiated with caution in patients with hepatic disease. Since finasteride is metabolized extensively in the liver, reduced metabolism is possible. The effect of hepatic impairment on finasteride pharmacokinetics has not been studied.
Patients with Renal Impairment Dosing
Specific guidelines for dosage adjustments in renal impairment are not available; it appears that no dosage adjustments are needed.
*non-FDA-approved indication
Saw Palmetto, Serenoa repens: (Moderate) Saw palmetto may inhibit 5 alpha-reductase, preventing the conversion of testosterone to dihydrotestosterone. This action is similar to the action of 5-alpha reductase inhibitors, such as dutasteride and finasteride. Co-use is likely to be common by patients, but the effects of co-use are not known. In theory, the effects could be additive, but it is not known if the added effects would be beneficial or harmful. Clinicians should be alert for any unusual effects if patients ingest saw palmetto supplements while taking 5-alpha reductase inhibitors.
Soy Isoflavones: (Minor) Theoretically, because the soy isoflavones appear to inhibit type II 5-alpha-reductase, the soy isoflavones may have additive effects with other 5-alpha reductase inhibitors.
Terazosin: (Minor) Terazosin has been reported to increase peak concentrations of finasteride by 16% and AUC by 31% when the two agents are coadministered. The interaction is of minor importance.
Finasteride is a synthetic 4-aza analog of testosterone that acts as a competitive, specific inhibitor of type II 5-alpha-reductase, an intracellular enzyme that converts testosterone to the potent androgen 5-alpha-dihydrotestosterone (DHT). The type II 5alpha-reductase isozyme is primarily found in prostate, seminal vesicles, epididymides, and hair follicles, as well as liver. The type II isozyme is responsible for two-thirds of circulating DHT. DHT is the primary androgen that stimulates the development of prostate tissue. When used for the treatment of benign prostatic hyperplasia, as the enzymatic conversion from testosterone to DHT is inhibited, a desirable reduction in prostate hypertrophy is achieved, and urine flow should be improved. In male pattern hair loss, the balding scalp contains miniaturized hair follicles and increased amounts of DHT compared with hairy scalp. Finasteride decreases scalp and serum DHT concentrations, thus interrupting a key factor in the development of androgenetic alopecia in those patients genetically predisposed. Finasteride does not appear to affect circulating concentrations of cortisol, estradiol, prolactin, thyroid-stimulating hormone, thyroxine or cholesterol. Research to date also suggests that finasteride does not affect the hypothalamic-pituitary-testicular-axis.
Finasteride is administered orally in men. Approximately 90% is bound to plasma proteins; yet the drug has been found to cross the blood-brain barrier. Finasteride generally does not affect other hormones. Finasteride has minimal distribution into semen. Data from 2 studies found semen drug concentrations ranged from undetectable (less than 0.1 ng/mL) to 10.54 ng/mL following daily treatments for 6 to 24 weeks. Daily dosing causes accumulation to occur, with plasma concentrations increasing by 50% over those observed from a single dose. The mean plasma elimination half-life of finasteride is 6 hours (range, 3 to 16 hours); however, the turnover rate for the type II 5-alpha-reductase enzyme complex is slow, with a turnover half-life of approximately 30 days. After oral dosing, about half of the unchanged drug is excreted in the feces, and one-third is metabolized in the liver to the 17-carboxylic acid, which is then excreted in the urine (39%) and the feces (57%).
A single 5 mg oral dose rapidly reduces serum DHT concentrations by as much as 70%, with the maximum reduction occurring at about 8 hours. The effect lasts for at least 24 hours, so once daily dosing is appropriate. Actual clinical effects, however, are not realized for 3 to 6 months after beginning therapy.
Affected cytochrome P450 (CYP450) isoenzymes and drug transporters: CYP3A4, UGT1A4
While finasteride is metabolized by hepatic CYP3A4 isoenzymes, no drug interactions of clinical importance have been identified, likely due to the hormonal mechanisms of action and relatively large therapeutic window of effect. Finasteride does not appear to affect the CYP450-linked drug metabolizing enzyme system. Compounds that have been tested in man have included antipyrine, digoxin, propranolol, theophylline, and warfarin and no clinically meaningful interactions were found. Finasteride has not been associated with clinically important drug interactions during clinical trials, including a 4-year safety trial of 3,040 males aged 45 to 78 years. Finasteride markedly inhibited UGT1A4 activity in vitro in a drug transporter study; however, the data strongly suggested that finasteride is unlikely to cause clinically significant drug-drug interactions mediated via inhibition of the hepatic UGT enzymes involved in drug metabolism in vivo.
-Route-Specific Pharmacokinetics
Oral Route
The mean bioavailability following a single dose of finasteride is about 63%; however, bioavailability is highly variable (range, 34% to 108%). Bioavailability is not affected by food, and maximum plasma concentrations (Cmax) are attained within 1 to 2 hours post dose.
-Special Populations
Hepatic Impairment
The effect of hepatic impairment on finasteride pharmacokinetics has not been studied.
Renal Impairment
Following administration of a single dose, the pharmacokinetics of finasteride (i.e., exposure, peak concentration, half-life, and protein binding) in patients with chronic renal impairment with a creatinine clearance (CrCl) 9 to 55 mL/minute were similar to those observed in healthy volunteers; however, plasma concentrations of the metabolites were significantly higher in patients with renal impairment. No dose adjustments are needed for decreased renal function.
Geriatric
Elimination of finasteride is reduced somewhat in the elderly, but no dosage adjustment is necessary.