Finasteride (Hair Growth) (Monograph)

Drug class: Cell Stimulants and Proliferants

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

Introduction

5α-reductase inhibitor.

Uses for Finasteride (Hair Growth)

Androgenetic Alopecia

Treatment of male pattern hair loss (androgenetic alopecia). Use in men only; not indicated in women or pediatric patients.

Based on current evidence demonstrating efficacy, finasteride is recommended as a first-line treatment of androgenetic alopecia in men. Assess response to treatment at 6 months; in some men, response may not become evident until 12 months.

If treatment is successful, continued therapy required to maintain efficacy.

For greater efficacy, may consider combination of oral finasteride and topical minoxidil.

Finasteride (Hair Growth) Dosage and Administration

General

Dispensing and Administration Precautions

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

Administration

Adminster orally without regard to meals.

Dosage

Adults

Androgenetic Alopecia in Men

Oral

1 mg once daily.

Daily administration for 3 months or longer generally necessary before benefit is observed. Continued use is recommended to sustain benefit, which should be reevaluated periodically; reversal of clinical benefit occurs within 1 year after discontinuance of finasteride.

Special Populations

Hepatic Impairment

Use with caution.

Renal Impairment

No dosage adjustment necessary.

Geriatric Patients

No dosage adjustment necessary.

Cautions for Finasteride (Hair Growth)

Contraindications

Pregnancy.
Hypersensitivity to any components of the medication.

Warnings/Precautions

Risk to Male Fetus

Not indicated for use in women. Females should not handle crushed or broken finasteride tablets if they are pregnant or potentially pregnant because of possibility of absorption and potential 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.

Effects on Prostate Specific Antigen (PSA)

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

Any confirmed increase in serum PSA concentration 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 to therapy with finasteride may also affect PSA results.

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

May increase risk of high-grade prostate cancer.

Specific Populations

Pregnancy

Contraindicated in women who are or may become pregnant. Type II 5α-reductase inhibitors inhibit conversion of testosterone to DHT and may cause abnormalities of the external genitalia of a male fetus.

If used during pregnancy, or if 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 women. 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

Clinical studies did not include patients ≥65 years of age. Manufacturer states no dosage adjustment is necessary in the elderly; however, efficacy of finasteride not established in this population.

Hepatic Impairment

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

Use with caution in patients with liver dysfunction.

Renal Impairment

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

Common Adverse Effects

Most common adverse reactions (≥1%): decreased libido, erectile dysfunction, ejaculation disorder.

Drug Interactions

Does not affect CYP enzyme system. No clinically meaningful drug interactions identified. Drugs tested for drug interaction potential with finasteride 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 (Hair Growth) Pharmacokinetics

Absorption

Bioavailability

Mean bioavailability of 1 mg tablets is 65%.

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 in liver primarily via CYP enzymes to 2 metabolites (t-butyl side chain monohydroxylated and monocarboxylic acid metabolites); metabolites exhibit no more than 20% of the 5α-reductase inhibitory activity of finasteride.

Elimination

Approximately 39% excreted in urine as metabolites and 57% excreted in feces.

Half-life

Approximately 5–6 hours in men 18–60 years of age and 8 hours in men >70 years of age.

Stability

Storage

Tablets

Store at room temperature (15–30°C); keep container closed and protect from moisture.

Actions

Competitive and specific inhibitor of Type II 5α-reductase, an intracellular enzyme that converts testosterone to DHT.
Type II isoenzyme is found predominantly in prostate, seminal vesicles, epididymides, and liver, and is detectable in the inner root sheath of hair follicles and epidermal keratinocytes.
Mechanism of action is based on preferential inhibition of Type II 5α-reductase, which blocks peripheral conversion of testosterone to DHT, resulting in substantial reductions in serum and tissue DHT concentrations.
In men with androgenetic hair loss, increased amounts of DHT and 5α-reductase lead to miniaturized hair follicles and shortened hair growth cycle.
Finasteride decreases scalp DHT concentrations to levels found in hairy scalp, reduces serum DHT, increases hair regrowth, and slows hair loss.
No affinity for androgen receptor and exhibits no androgenic, antiandrogenic, estrogenic, antiestrogenic, or progestational effects.

Advice to Patients

Advise patients to read the FDA-approved patient labeling (Patient Information).
Inform patients that women 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 potential risk to a male fetus. The tablets are coated and will prevent contact with the active ingredient during normal handling, provided the tablets have not been broken or crushed. If a woman 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 there was an increase in high-grade prostate cancer in men treated with 5α-reductase inhibitors indicated for BPH treatment, compared to those treated with placebo in clinical studies. The screening blood test for prostate cancer (PSA) may be affected by finasteride. Advise patients to inform providers if they are taking finasteride or if they have not taken finasteride as prescribed prior to having a PSA test performed.
Inform patients that finasteride may cause symptoms of sexual dysfunction such as decreased libido, erectile dysfunction, and ejaculation disorder, including decreased ejaculate volume.
Breast changes including breast enlargement, tenderness, and neoplasm have been reported. Advise patients to promptly report any changes in their breasts such as lumps, pain, or nipple discharge.
Instruct patients to read the patient package insert before starting therapy with finasteride and to read it again each time the prescription is renewed so that they are aware of current information regarding the drug.
Advise patients 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.