Finasteride

Finasteride is a type-II 5-alpha-reductase inhibitor used principally for benign prostatic hyperplasia in intact male dogs. It reduces androgen-driven prostatic enlargement while generally preserving circulating testosterone and reproductive function. This makes it useful in selected breeding dogs or other patients in which medical reduction of prostate size is preferred.

Group

5-alpha-reductase inhibitor

Mechanism of Action

Finasteride inhibits conversion of testosterone to dihydrotestosterone within androgen-responsive tissues. Because dihydrotestosterone is a potent driver of prostatic growth, reduced intraprostatic availability decreases androgen stimulation and promotes gradual involution of hyperplastic tissue. The reduction in prostate volume can lessen compression and bleeding associated with benign enlargement without directly eliminating testicular testosterone production.

Dose Rates

Dog

Use / stage	Dose	Route	Schedule	Instructions
Benign prostatic hyperplasia	0.1 mg/kg	PO	Every 24 h	Do not use in: Pregnancy
Benign prostatic hyperplasia	0.1–0.5 mg/kg	PO	Every 24 h	Do not use in: Pregnancy; Alternative studied range.
Benign prostatic hyperplasia	5 mg/animal	PO	Every 24 h	Do not use in: Pregnancy; Source fixed regimen for dogs weighing 10–50 kg.
Size-selected prostatic hyperplasia regimen	Reference only	PO		Alternative daily fixed amounts: 1.5 mg if under 15 kg, 2.5 mg at 15–30 kg, or 5 mg above 30 kg. The source describes 1.5 mg as approximately one-third of a 5 mg tablet, which is arithmetically inexact; the milligram amount and fraction must not be treated as equal.

Ferret

Use / stage	Dose	Route	Schedule	Instructions
Adrenal-disease adjunct	5 mg	PO	Every 24 h

Indications

Medical treatment of benign prostatic hyperplasia in intact male dogs, including breeding dogs, to reduce prostate size and associated signs such as bloody urethral discharge, hematuria or defecatory straining.

Contraindications

Pregnancy
Food-producing animals

Interactions

May be used with an alpha-blocker such as tamsulosin.

Adverse effects

No specific canine adverse effects reported in the supplied limited studies.

Preparations

Preparation	Form	Strength	Route
Finasteride 1 mg	Tablet	1 mg / tablet	PO
Finasteride 5 mg	Tablet	5 mg / tablet	PO

Monitoring and Administration

Assess prostate size and clinical signs; semen quality and testosterone production were preserved in cited canine studies.