Finasteride

5α-reductase inhibitor, Benign prostatic hyperplasia treatment, Androgen modulator

Finasteride

Proscar (5 mg, BPH), Propecia (1 mg, alopecia)

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Summary

Classes

5α-reductase inhibitor, Benign prostatic hyperplasia treatment, Androgen modulator

Common uses

Benign prostatic hyperplasia0, Androgenetic alopecia (male pattern hair loss)0, Off-label: hirsutism, feminizing GAHT adjunct0

Pharmacy

Starting dose

5 mg PO daily for BPH; 1 mg PO daily for androgenetic alopecia

Preparations

1 mg, 5 mg tablets

US FDA Max

5 mg/d

Pharmacology

Routes

Oral

Onset

BPH symptom improvement at 3-6 months; prostate volume reduction over 6-12 months; hair regrowth at 6-12 months

Duration

24 hours

Half-life

~5-6 hours in young men, ~8 hours in elderly^[1]

Bioavailability

~63% (oral)^[1]

Pregnancy

Pregnant individuals should not handle crushed/broken tablets (skin absorption risk); can cause hypospadias in male fetus. Not used in pregnancy.^{[citation needed]}

Legal status

Rx-only in US

Purported mechanism

Finasteride is a selective inhibitor of type II 5α-reductase, the dominant prostatic isoform converting testosterone to dihydrotestosterone (DHT); DHT lowering ~70% shrinks androgen-dependent prostatic tissue and the dermal papilla of androgen-sensitive hair follicles.0 Dutasteride inhibits both type I and II isoforms with deeper DHT suppression but a similar clinical effect. Post-finasteride syndrome (persistent sexual and mood effects after discontinuation) is a controversial but recognized clinical concern that the FDA acknowledged in 2012 labeling^[1].

References

↑ ^1.0 ^1.1 ^1.2 FDA Prescribing Information, Proscar (finasteride), Merck, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2014/020180s044lbl.pdf

[proscar-label-1] 1.0 ^1.1 ^1.2 FDA Prescribing Information, Proscar (finasteride), Merck, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2014/020180s044lbl.pdf

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