Finasteride

INTRODUCTION

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.

Adverse Reactions/Side Effects

GU: decreased libido, decreased volume of ejaculate, erectile dysfunction.

PHYSICAL THERAPY IMPLICATIONS

Examination and Evaluation

• When treating BPH, monitor signs such as difficulty starting a urine stream, painful urination, weak urine flow, feeling that the bladder is not completely empty, frequent nighttime urination, and an urge to urinate again soon after urinating. Document any change in BPH symptoms to help assess the effects of drug therapy.

Interventions

• When appropriate, design and implement resistive exercise programs to help maintain muscle strength and bone integrity to offset the musculoskeletal effects of diminished 5-alpha-dihydrotestosterone biosynthesis.

Patient/Client-Related Instruction

• When treating BPH, advise patient that urinary symptoms (retention, dribbling, hesitancy, urgency) should improve, and to contact the physician if these symptoms continue to worsen.

• Instruct patient to report other bothersome side effects such as decreased libido or erectile dysfunction.

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; slightly increased in patients >70 yr).

Contraindications/Precautions

Contraindicated in: Hypersensitivity; Women.

Use Cautiously in: Patients with hepatic impairment or obstructive uropathy.

Interactions

Drug-Drug: None noted.

Route/Dosage

PO (Adults): BPH—5 mg once daily (Proscar); androgenetic alopecia—1 mg/day (Propecia).

Availability (generic available)

Tablets: 1 mg (Propecia), 5 mg (Proscar).