5 Alpha Reductase Inhibitors

5-alpha reductase is responsible for converting testosterone to dihydrotestosterone (DHT).  DHT is more potent than testosterone and mediates normal sexual development in males, prostate gland growth, male pattern baldness, and pubic and facial hair growth.  Blockage of 5-alpha reductase reduces DHT levels.  As would be expected, 5-alpha reductase inhibitors are used to reduce prostate gland growth. Finasteride also has indications for topical treatment of male pattern baldness.  Side effects include decreased libido, impotence, and gynecomastia.

Class Drugs

• Dutasteride

• Finasteride

Class Mechanism of Action

Blocks 5-alpha reductase, reducing production of dihydrotestosterone (DHT)

• DHT mediates normal sexual development in males, prostate gland growth, male pattern baldness, and pubic and facial hair growth.

Class Applications

Benign prostatic hypertrophy (BPH)

Alopecia (dihydrotestosterone stimulates hair loss)

Class Adverse Effects

Oligospermia, erectile dysfunction

Decreased libido

Gynecomastia

Teratogenic potential

• Women who are or may become pregnant should not handle or ingest

Can cause defects in formation of male genitalia (hypospadias)

Drug Table

Drug Name	Application	Comments	Image
Dutasteride			"Duty Free" "Asteroid"
Finasteride	Applied topically to reduce DHT levels in hair follicles		"Fin" "Asteroid"