finasteride

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: 63% absorbed following oral administration.

Distribution: Enters prostatic tissue and crosses the blood-brain barrier. Remainder of distribution not known.

Protein Binding: 90%.

Metabolism/Excretion: Mostly metabolized; 39% excreted in urine as metabolites; 57% excreted in feces.

Half-Life: 6 hr (range 6–15 hr; slightly ↑ in patients >70 yr).

Time/Action Profile ⬆ ⬇

(↓ 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 months and remain for 4 mo after discontinuation.

Contraind./Precautions ⬆ ⬇

Contraindicated in:

Hypersensitivity.

Use Cautiously in:

Hepatic impairment;
Obstructive uropathy.

Adv. Reactions/Side Effects ⬆ ⬇

Endo: gynecomastia

GU: ↓libido, ↓volume of ejaculate, erectile dysfunction, infertility, PROSTATE CANCER (HIGH-GRADE)

Misc: ANGIOEDEMA, BREAST CANCER

Interactions ⬆ ⬇

Drug-drug:

None reported.

Route/Dosage ⬆ ⬇

Benign Prostatic Hypertrophy

PO (Adults ): Proscar: 5 mg once daily.

Androgenetic Alopecia

PO (Adults ): Propecia: 1 mg once daily.

Availability ⬆ ⬇

(Generic available)

Tablets (Proscar): 5 mg
Tablets (Propecia): 1 mg
In combination with: tadalafil (Entadfi). See Appendix [not included in this PDA edition].

Assessment ⬆ ⬇

Assess for symptoms of prostatic hyperplasia (urinary hesitancy, feeling of incomplete bladder emptying, interruption of urinary stream, impairment of size and force of urinary stream, terminal urinary dribbling, straining to start flow, dysuria, urgency) before and periodically during therapy.
Digital rectal examinations should be performed before and periodically during therapy for BPH.

Lab Test Considerations:

Establish a new baseline serum prostate-specific antigen (PSA) concentration ≥6 mo after initiating treatment and periodically during therapy. Finasteride may cause a ↓ in serum PSA levels. Any confirmed ↑ from lowest PSA value while on Propecia may be a sign of prostate cancer and should be evaluated, even if PSA levels are within the normal range for men not taking a 5α-reductase inhibitor.

Implementation ⬆ ⬇

Do not confuse Proscar with Prograf or Provera.
When cutting, crushing, or handling tablets, wear double chemotherapy gloves, protective gown, and hair and shoe covers. Prepare in a ventilated engineering control, if possible, and consider crushing tablets in a pill pouch. Use respiratory (N95) protection and eye and face protection, if not prepared in a ventilated engineering control. During administration, wear double chemotherapy gloves and protective gown when handling uncoated, cut, or crushed tablets. Eye/face protection is need if there is risk of patient vomiting or spitting up. Single chemotherapy gloves are appropriate if handling and administering intact tablets from a unit-dose package. Those who are actively trying to conceive, who are pregnant or may become pregnant, and who are breastfeeding should avoid handling finasteride.
PO: Administer once daily with or without meals.

Patient/Family Teaching ⬆ ⬇

Explain the purpose and side effects of finasteride. Instruct patient to take as directed, even if symptoms improve or are unchanged. ≥6–12 mo of therapy may be necessary to determine whether or not an individual will respond to finasteride. If a dose is missed, omit and take next tablet at usual time. Advise patient to read the Patient Information prior to starting therapy and with each Rx refill in case of changes.
Emphasize the importance of periodic follow-up exams to determine whether a clinical response has occurred.
Inform patient that the volume of ejaculate may be ↓ and erectile dysfunction and ↓ libido may occur during therapy and after therapy is completed.
Advise patient to notify health care professional promptly if changes in breasts (lumps, pain, nipple discharge) occur.
Inform patient that there is an ↑ risk of high-grade prostate cancer in men taking this drug.
Advise patient to notify health care professional of all Rx or OTC medications, vitamins, or herbal products being taken and to consult with health care professional before taking other medications.
Rep: May cause fetal harm. Caution patient that finasteride poses a potential risk to a male fetus. Women who are pregnant or may become pregnant should avoid exposure to semen of a partner taking finasteride and should not handle crushed finasteride due to potential absorption.

section name header

Pronunciation ⬇

Classifications ⬆ ⬇

Indications ⬆ ⬇

Action ⬆ ⬇