Brand names: Entadfi; , Proscar
Drug class: 5-alpha-Reductase Inhibitors

Medically reviewed by Drugs.com on May 10, 2024. Written by ASHP.

Introduction

Inhibitor of 5α-reductase, an intracellular enzyme necessary for conversion of testosterone to 5α-dihydrotestosterone (DHT).

Uses for Finasteride (BPH)

Benign Prostatic Hyperplasia

Used as monotherapy for treatment of symptomatic benign prostatic hyperplasia (BPH) in men with an enlarged prostate to improve symptoms, reduce risk of acute urinary retention, and reduce risk of surgery including transurethral resection of theprostate (TURP) and prostatectomy.

May be used in combination with an α-blocker (e.g., doxazosin) to reduce risk of symptomatic progression of BPH (a confirmed ≥4 point increase inAmerican Urological Association [AUA] symptom score).

Also may be used in combination with tadalafil, a phosphodiesterase (PDE) type 5 inhibitor, for treatment of signs and symptoms of BPH. A fixed-combination preparation (finasteride/tadalafil; Entadfi) is commercially available for initial treatment of signs and symptoms of BPH in men with an enlarged prostate for up to 26 weeks; the incremental benefit of tadalafil beyond 26 weeks is unknown.

AUA guidelines consider 5α-reductase inhibitor monotherapy an appropriate option for symptomatic treatment of lower urinary tract symptoms in patients with BPH who have evidence of prostatic enlargement. A 5α-reductase inhibitor, alone or in combination with an α₁-adrenergic blocker, is recommended as a treatment option to prevent progression of lower urinary tract symptoms and/or reduce risks of urinary retention and need for future prostate-related surgery in patients with demonstrable prostatic enlargement.

AUA guidelines state that the combination of low-dose daily tadalafil 5 mg with finasteride may be considered for treatment of lower urinary tract symptoms of BPH; however, long-term data are lacking and such combination therapy is thought to offer little to no advantages in symptom improvement over finasteride alone in the short term.

Not indicated for use in female patients or in pediatric patients.

Not approved for prevention of prostate cancer.

Related/similar drugs

tamsulosin, finasteride, estradiol, tadalafil, Flomax, prazosin, Cialis

Finasteride (BPH) Dosage and Administration

General

Pretreatment Screening

• Prior to initiating treatment for BPH, consider other urological conditions that may cause similar symptoms. In addition, consider that prostate cancer and BPH may coexist.

Patient Monitoring

• Carefully monitor patients with a large residual urinary volume and/or severely diminished urinary flow for obstructive uropathy; such patients may not be candidates for finasteride.

Dispensing and Administration Precautions

Handling and Disposal

• Females who are pregnant or who may become pregnant should not handle crushed or broken finasteride tablets because of the possibility of drug absorption and subsequent potential risk to a male fetus.

Administration

Administer finasteride orally without regard to meals. Administer finasteride/tadalafil orally on an empty stomach.

Dosage

Adults

Benign Prostatic Hypertrophy

Oral

5 mg once daily, either alone or in combination with doxazosin.

While early symptomatic improvement may occur, 6 months or more of therapy may be necessary to determine clinical benefit.

Dosage of the fixed-combination finasteride/tadalafil preparation is 5 mg of finasteride and 5 mg of tadalafil taken once daily on an empty stomach at approximately the same time every day for up to 26 weeks; use not recommended for more than 26 weeks because incremental benefit of tadalafil after this time period not known.

Special Populations

Hepatic Impairment

Use with caution.

Renal Impairment

No dosage adjustment necessary.

Geriatric Patients

No dosage adjustment necessary.

Cautions for Finasteride (BPH)

Contraindications

• Pregnancy.

• Hypersensitivity to any components of the medication.

Warnings/Precautions

Effects on Prostate Specific Antigen (PSA)

Finasteride decreases PSA levels. Consider such reductions when interpreting PSA values in men receiving the drug.

Establish a new PSA baseline at least 6 months after starting treatment and monitor PSA periodically thereafter.

Any confirmed increase in serum PSA concentration from the lowest PSA value while taking finasteride may signal presence of prostate cancer and should be evaluated, even if PSA levels are still within the normal range for men not taking a 5α-reductase inhibitor.

Noncompliance with therapy can also affect PSA results.

Finasteride also may cause decreased PSA levels in the presence of prostate cancer.

Increased Risk of High-grade Prostate Cancer with 5α-Reductase Inhibitors

May increase risk of high-grade prostate cancer. Not labeled by FDA for prevention of prostate cancer.

Risk to Male Fetus

Not indicated for use in women. Females should not handle crushed or broken finasteride tablets if pregnant or potentially pregnant because of possibility of drug absorption and risk to a male fetus. (See Pregnancy under Cautions.)

Finasteride tablets are coated and will prevent contact with the active ingredient during normal handling, provided the tablets have not been broken or crushed.

Effect on Semen

No clinically meaningful effects on sperm parameters (e.g., concentration, mobility, morphology, or pH) observed in healthy volunteers. Although decreased ejaculate volume and concomitant reduction in total sperm per ejaculate observed, these parameters remained within normal range and were reversible upon drug discontinuation.

Consideration of Other Urological Conditions

Prior to initiating treatment, consider other urological conditions that may cause similar symptoms. In addition, consider that prostate cancer and BPH may coexist.

Monitor patients with a large residual urinary volume and/or severely diminished urinary flow carefully for obstructive uropathy; such patients may not be candidates for finasteride.

Use of Fixed Combinations

When finasteride is used in fixed combination with tadalafil, the usual cautions, precautions, and contraindications associated with tadalafil must be considered in addition to those associated with finasteride.

Specific Populations

Pregnancy

Contraindicated in women who are or may become pregnant. Because Type II 5α-reductase inhibitorsinhibit conversion of testosterone to DHT, finasteridemay cause abnormalities of the external genitalia in male fetuses.

If used during pregnancy, or patient becomes pregnant while taking the drug, apprise patient of potential hazard to male fetus.

In animal studies, finasteride caused abnormal development of external genitalia in male fetuses.

Lactation

Not indicated for use in females. Not known whether drug is distributed into human milk.

Females and Males of Reproductive Potential

Not indicated for use in women. Contraindicated in women who are or may become pregnant.

Pediatric Patients

Not indicated for use in pediatric patients.

Geriatric Use

Although elimination is decreased in geriatric patients, no dosage adjustment necessary.

Hepatic Impairment

Extensively metabolized in the liver; effect of hepatic impairment on finasteride pharmacokinetics not established.

Renal Impairment

Finasteride AUC, peak plasma concentration, elimination half-life, and protein binding in patients with chronic renal failure (Cl_cr 9–55 mL/minute) were similar to those in healthy individuals; no dosage adjustment necessary in patients with renal insufficiency.

Common Adverse Effects

Most common adverse effects (≥1%): impotence, decreased libido, decreased volume of ejaculate, breast enlargement, breast tenderness, rash.

Drug Interactions

Does not affect CYP enzyme system. No clinically meaningful drug interactions identified. Drugs that have been tested for drug interaction potential include antipyrene, digoxin, propranolol, theophylline, and warfarin.

Although specific drug interaction studies not performed, finasteride was used concomitantly with the following drugs in clinical studies without evidence of clinically significant adverse interactions: acetaminophen, acetylsalicylic acid, α-blockers, analgesics, angiostensin-converting enzyme (ACE) inhibitors, anticonvulsants, benzodiazepines, beta-blockers, calcium-channel blockers, cardiac nitrates, diuretics, H₂antagonists, HMG-CoA reductase inhibitors, NSAIAs, and quinolone anti-infectives.

Finasteride (BPH) Pharmacokinetics

Absorption

Bioavailability

Mean bioavailability of 5-mg tablets is 63%.

Plasma Concentrations

Peak plasma concentrations achieved within 1 to 2 hours following a dose.

Food

Bioavailability not affected by food.

Distribution

Extent

Crosses blood-brain barrier.

Plasma Protein Binding

Approximately 90% of circulating finasteride is bound to plasma proteins.

Elimination

Metabolism

Extensively metabolized, primarily by CYP3A4.

Active metabolites retain no more than 20% of the 5α-reductase inhibitory activity of parent drug.

Elimination

Excreted in the urine (mean 39%, range 32-46%) and feces (mean 57%, range 51-64%).

Half-life

6 (range, 4-12) hours in patients 45-60 years of age.

8 (range, 6-15) hours in patients ≥70 years of age.

Stability

Storage

Tablets

Store at room temperature (below 30°C); protect from light and keep container tightly closed.

Actions

• Competitive and specific inhibitor of Type II 5α-reductase, an intracellular enzyme that converts testosterone to 5α-dihydrotestosterone (DHT).

• DHT is the principal androgen responsible for stimulation of prostatic growth.

• Finasteride inhibits 5α-reductase by forming a stable enzyme complex; turnover from the complex is slow (half-life of about 30 days).

• No affinity for the androgen receptor.

Advice to Patients

• Advise the patient to read the FDA-approved patient labeling (Patient Information).

• Inform patients that there was an increase in high-grade prostate cancer in men treated with 5α-reductase inhibitors indicated for BPH treatment, including finasteride, compared to those treated with placebo in studies evaluating use of these drugs for prevention of prostate cancer. Advise patients that laboratory monitoring of prostate-specific antigen is recommended.

• Inform patients that females who are pregnant or may potentially be pregnant should not handle crushed or broken finasteride tablets because of the possibility of absorption of finasteride and the subsequent risk to the male fetus. Finasteride tablets are coated and will prevent contact with the active ingredient during normal handling, provided that the tablets have not been broken or crushed. If a female who is pregnant or may potentially be pregnant comes in contact with crushed or broken finasteride tablets, the contact area should be washed immediately with soap and water.

• Inform patients that the volume of ejaculate may be decreased during treatment with finasteride. This does not appear to interfere with normal sexual function. However, impotence and decreased libido may occur in patients treated with the drug.

• Instruct patients to promptly report any changes in their breasts such as lumps, pain or nipple discharge. Breast changes including breast enlargement, tenderness and neoplasm have been reported.

• Advise that some patients do not respond to finasteride. Patients should inform their clinican if they experience large residual urinary volume and/or severly diminshed urinary flow.

• Advise patient to inform their clinician of existing or contemplated concomitant therapy, including prescription and OTC drugs and dietary or herbal supplements, as well as any concomitant illnesses.

• Inform patients of other important precautionary information.

Additional Information

The American Society of Health-System Pharmacists, Inc. represents that the information provided in the accompanying monograph was formulated with a reasonable standard of care, and in conformity with professional standards in the field. Readers are advised that decisions regarding use of drugs are complex medical decisions requiring the independent, informed decision of an appropriate health care professional, and that the information contained in the monograph is provided for informational purposes only. The manufacturer’s labeling should be consulted for more detailed information. The American Society of Health-System Pharmacists, Inc. does not endorse or recommend the use of any drug. The information contained in the monograph is not a substitute for medical care.

Preparations

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

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