Finasteride

Pronunciation: fih-NASS-teer-IDE
Class: Androgen hormone inhibitor

Trade Names

Propecia
- Tablets 1 mg

Proscar
- Tablets 5 mg

Pharmacology

Inhibits conversion of testosterone into 5-alpha-dihydrotestosterone, a potent androgen.

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Pharmacokinetics

Absorption

Mean bioavailability is 65% (range, 26% to 170%). C _max at steady state is 4.9 to 13.7 ng/mL (mean, 9.2 ng/mL) ( Propecia ). C _max is 37 ng/mL (range, 27 to 49 ng/mL) ( Proscar ). T _max is 1 to 2 h. AUC _0-24 is 20 to 154 ng•h/mL (mean, 53 ng•h/mL).

Distribution

Vd _ss is 44 to 96 L (mean, 76 L) and is about 90% bound to plasma proteins. The drug crosses the blood-brain barrier but does not appear to distribute preferentially to the CSF.

Metabolism

Extensively metabolized in the liver, primarily via the CYP-450 3A4 enzyme subfamily. Two metabolites have been identified: t-butyl side chain monohydroxylated and monocarboxylic acid; each possesses no more than 20% activity.

Elimination

Plasma Cl is 70 to 279 mL/min (mean, 165 mL/min). Mean t _½ is 4.8 h (range, 3.3 to 13.4 h) ( Propecia ). Mean t _½ is 6 h (range, 3 to 16 h) ( Proscar ); 32% to 46% is excreted in the urine as metabolites, and 51% to 64% is excreted in the feces.

Special Populations

Mean t _½ increases to 8 h (70 yr of age and older). Mean AUC _0-24 increases 15%.

Indications and Usage

Treatment of male pattern hair loss (androgenic alopecia) in men only.

Treatment of symptomatic benign prostatic hyperplasia (BPH) in men with enlarged prostate; in combination with doxazosin to reduce the risk of symptomatic progression of BPH.

Contraindications

Use during pregnancy; use in women or children.

Dosage and Administration

PO Propecia : 1 mg daily. Proscar : 5 mg daily.

Drug Interactions

None well documented.

Laboratory Test Interactions

Decreased prostate-specific antigen levels.

Adverse Reactions

Cardiovascular

Postural hypotension (9%); hypotension (1%).

CNS

Decreased libido (2%).

Decreased libido (10%); dizziness (7%); headache, somnolence (2%).

Genitourinary

Erectile dysfunction, ejaculation disorders (1%); breast tenderness/enlargement in men (postmarketing).

Impotence (19%); abnormal ejaculation (7%); decreased volume of ejaculate (4%); abnormal sexual function (3%); breast enlargement in men (2%).

Hypersensitivity

Pruritus, urticaria, swelling of lips and face, testicular pain (postmarketing).

Metabolic

Peripheral edema (1%).

Respiratory

Rhinitis (1%).

Miscellaneous

Asthenia (5%).

Precautions

Pregnancy

Category X .

Lactation

Undetermined.

Children

Safety and efficacy not established.

Hepatic Function

Use with caution.

Carcinogenesis

Based on animal studies, may have carcinogenic or mutagenic potential.

Duration of therapy

Minimum 6 mo therapy may be necessary to see effect ( Proscar ). Minimum 3 mo therapy may be necessary to see effect ( Propecia ).

Obstructive uropathy

Carefully monitor patients with large residual urine volume or severely diminished urinary flow.

Prostate-specific antigen (PSA) levels

Carefully evaluate any increase in PSA level, consider noncompliance with therapy.

Patient Information

• Advise patient to read patient information leaflet before starting therapy and with each refill.
• Advise patient to take prescribed dose once daily without regard to meals but to take with food if stomach upset occurs.
• Caution patient that women of childbearing potential should not handle crushed or broken tablets.
• Advise patient being treated for BPH that finasteride may be used by itself or in combination with doxazosin.
• Advise patient being treated for BPH that although symptoms may improve early in treatment, it may take 6 to 12 mo for full benefit to be noted.
• Advise patient being treated for male pattern baldness that it may take 3 mo or more of daily therapy before improvement is noted and that continued use is required to maintain benefit. Advise patient that stopping therapy will result in reversal of effect within 12 mo.
• Advise patient being treated for BPH to notify health care provider if urinary symptoms do not improve or worsen while taking this medication.
• Advise patient that volume of ejaculate may be decreased but that this does not appear to interfere with normal sexual function in most patients. Advise patient to notify health care provider if sexual dysfunction (eg, decreased libido, impotence) develops while taking finasteride.
• Instruct patient to immediately report breast lumps, breast pain, or nipple discharge.

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