finasteride (fi-nas-teer-ide) Propecia, Proscar

 Indications

Benign prostatic hyperplasia (BPH); can be used with

doxazosin. Androgenetic alopecia (male pattern baldness)

in men only.

Action

Inhibits the enzyme 5-alpha-reductase, which is responsible

for converting testosterone to its potent metabolite

5-alpha-dihydrotestosterone in prostate, liver,

and skin; 5-alpha-dihydrotestosterone is partially responsible

for prostatic hyperplasia and hair loss.

Therapeutic Effects: Reduced prostate size with

associated decrease in urinary symptoms. Decreases

hair loss; promotes hair regrowth.

Pharmacokinetics

Absorption: Well absorbed after oral administration

(63%).

Distribution: Enters prostatic tissue and crosses the

blood-brain barrier. Remainder of distribution not

known.

Protein Binding: 90%.

Metabolism and Excretion: Mostly metabolized;

39% excreted in urine as metabolites; 57% excreted in

feces.

Half-life: 6 hr (range 6–15 hr; slightlyqin patients

70 yr).

TIME/ACTION PROFILE (p in

dihydrotestosterone levels†)

ROUTE ONSET PEAK DURATION

PO rapid 8 hr 2 wk

†Clinical effects as noted by urinary tract symptoms and hair

regrowth may not be evident for several mo and remain for 4

mo after discontinuation.

Contraindications/Precautions

Contraindicated in: Hypersensitivity; Women.

Use Cautiously in: Patients with hepatic impairment

or obstructive uropathy.

Adverse Reactions/Side Effects

Endo: gynecomastia. GU: PROSTATE CANCER (HIGHGRADE),

plibido,pvolume of ejaculate, erectile dysfunction,

infertility. Misc: ANGIOEDEMA, BREAST CANCER.

Interactions

Drug-Drug: None noted.

Route/Dosage

PO (Adults): BPH—5 mg once daily (Proscar); Androgenetic

alopecia—1 mg once daily (Propecia).

Availability (generic available)

Tablets: 1 mg (Propecia), 5 mg (Proscar). Cost: Generic—

1 mg $134.61/100, 5 mg $21.85/100.