5α-reductase inhibitors (or 5-alpha-reductase inhibitors) are a group of drugs with antiandrogenic activity, used in the treatment of benign prostatic hyperplasia and androgenic (or androgenetic) alopecia. These drugs decrease the levels of available 5α-reductase prior to testosterone binding with the enzyme, thus reducing levels of dihydrotestosterone that derives from such a bond.

Clinical use

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Indications

5α-reductase inhibitors are clinically used in the treatment of conditions which are exacerbated by dihydrotestosterone. Specifically, these indications may include: (Rossi, 2004)

• mild-to-moderate benign prostatic hyperplasia
• androgenic (or androgenetic) alopecia

Adverse drug reactions

Adverse drug reactions (ADRs) experienced with 5α-reductase inhibitors are generally dose-dependent. Common ADRs include impotence, decreased libido, decreased ejaculate volume. Rare ADRs include: breast tenderness and enlargement, and allergic reaction. (Rossi, 2004)

Pharmacology

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The enzyme 5α-reductase is involved in the conversion of testosterone to the active form dihydrotestosterone by reducing the Δ4,5 double-bond. In benign prostatic hyperplasia, dihydrotestosterone acts as a potent cellular androgen and promotes prostate growth - inhibiting the enzyme reduces the excessive prostate growth. In alopecia, pattern-baldness is one of the effects of androgenic receptor activation. Reducing the levels of dihydrotestosterone thus reduces alopecia.

Examples

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• finasteride (Proscar, Propecia)
• dutasteride (Avodart)
• FCE 28260, an experimental compound

Reference

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• Rossi S (Ed.) (2004). Australian Medicines Handbook 2004. Adelaide: Australian Medicines Handbook. ISBN 0-9578521-4-2

5-alpha-reductase inhibitors