finasteride
Propecia, Proscar

Available forms
Available by prescription only
Tablets: 1 mg, 5 mg

Indications and dosages
 Symptomatic BPH. Proscar. Adult men: 5 mg P.O. daily, usually for 6 to 12 months.
 Male pattern baldness. Propecia. Adult men: 1 mg P.O. daily, usually for 3 months or longer. Continued use is recommended to sustain benefit. Withdrawal of treatment leads to reversal of effect within 12 months.

Pharmacodynamics
Androgen synthesis inhibition action: Finasteride competitively inhibits steroid 5α-reductase, an enzyme responsible for formation of the potent androgen 5α-dihydrotestosterone (DHT) from testosterone. Finasteride has a greater affinity for Type II 5α-reductase than Type I and lacks affinity for the androgen receptor. Because DHT influences development of the prostate gland, decreasing levels of this hormone in men should relieve the symptoms associated with BPH. In men with male pattern baldness, the balding scalp contains miniaturized hair follicles and increased amounts of DHT. Finasteride decreases scalp and serum DHT levels in these men.

Pharmacokinetics
Absorption: Average bioavailability of drug was 63% in one study.
Distribution: About 90% bound to plasma proteins. Drug crosses the blood-brain barrier.
Metabolism: Extensively metabolized by the liver; at least 2 metabolites have been identified. Metabolites are responsible for less than 20% of total activity of the drug.
Excretion: Part of oral dose (39%) is excreted in urine as metabolites; 57% is excreted in feces. No unchanged drug is found in urine.

Contraindications and precautions
Contraindicated in patients hypersensitive to drug and in women (pregnant and not pregnant) and children. Use cautiously in patients with hepatic impairment.

Interactions
Drug-drug. Theophylline: Causes clinically insignificant increases in theophylline clearance and decreased half-life (10%). Use together cautiously.

Adverse reactions
GU: impotence, decreased ejaculate volume.
Other: decreased libido.

Effects on lab test results
• May decrease prostate-specific antigen (PSA) serum levels.

Overdose and treatment
Experience with overdose is limited. Patients have received single doses of 400 mg and doses of up to 80 mg daily for 3 months without adverse effects.

Special considerations
• Closely evaluate patient for conditions that might mimic BPH before therapy, including hypotonic bladder, prostate cancer, infection, stricture, or other neurologic conditions.
 ALERT All women of childbearing age should avoid exposure to drug and semen of patient receiving this drug. Exposure to broken or crushed tablets or to semen of treated patient during pregnancy presents hazard to male fetus.
 ALERT Finasteride has different trade names for products with different indications using the same active ingredient. Be alert for duplication or triplication of medication.
• Because it isn’t possible to identify prospectively which patients will respond to finasteride, a minimum of 6 months of therapy may be needed.
• Long-term effects of drug on the complications of BPH, including acute urinary obstruction or the need for surgery, aren’t known.
• Current investigations aim to determine effectiveness of drug as adjuvant therapy after radical prostatectomy; as adjunctive treatment of prostate cancer; acne, and hirsutism.
• PSA levels are decreased by 50% in patients with BPH who are taking finasteride.
• Carefully monitor patients who have large residual urine volumes or severely diminished urine flows. Not all patients respond to drug, and these patients may not be candidates for finasteride therapy.
• Carefully evaluate sustained increases in serum PSA. In patients receiving finasteride therapy, this could indicate noncompliance to therapy.
Pregnant patients
• Not indicated for use in women; potential hazard to male fetus when pregnant women come in contact with broken or crushed tablet or semen of male patient receiving drug.
Breast-feeding patients
• It isn’t known whether drug appears in breast milk; however, it isn’t indicated for use in women.
Pediatric patients
• Drug isn’t indicated for use in children.
Geriatric patients
• Although elimination of drug is decreased in elderly patients, dosage adjustments aren’t needed.

Patient education
• Advise patient that anyone who is or may become pregnant must not handle crushed tablets or have contact with patient’s semen because of risk of adverse effects on a male fetus.
• Explain that drug may decrease the volume of ejaculate but doesn’t appear to impair normal sexual function. However, impotence and decreased libido have occurred in less than 4% of patients treated with drug.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use