Class: Androgen hormone inhibitor
- Tablets 1 mg
- Tablets 5 mg
Inhibits conversion of testosterone into 5-alpha-dihydrotestosterone, a potent androgen.
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).
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.
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.
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.
Mean t ½ increases to 8 h (70 yr of age and older). Mean AUC 0-24 increases 15%.
Indications and UsagePropecia
Treatment of male pattern hair loss (androgenic alopecia) in men only.Proscar
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.
Use during pregnancy; use in women or children.
Dosage and AdministrationAdults
PO Propecia : 1 mg daily. Proscar : 5 mg daily.
None well documented.
Laboratory Test Interactions
Decreased prostate-specific antigen levels.
Postural hypotension (9%); hypotension (1%).
Decreased libido (2%).Proscar
Decreased libido (10%); dizziness (7%); headache, somnolence (2%).
Erectile dysfunction, ejaculation disorders (1%); breast tenderness/enlargement in men (postmarketing).Proscar
Impotence (19%); abnormal ejaculation (7%); decreased volume of ejaculate (4%); abnormal sexual function (3%); breast enlargement in men (2%).
Pruritus, urticaria, swelling of lips and face, testicular pain (postmarketing).
Peripheral edema (1%).
Category X .
Safety and efficacy not established.
Use with caution.
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 ).
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.
- 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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