By Rania Gollakner, BS, DVM, MPH

What is finasteride?

Finasteride (brand names Proscar®, Propecia®) is a medication used in dogs to restore infertility issues caused by benign prostatic hypertrophy (an enlargement of the prostate gland caused by hormones) and to treat the general clinical signs associated with it. Finasteride can reduce the size of the prostate without affecting the production of testosterone or the quality of semen in dogs used for breeding. In intact, non-breeding dogs, finasteride can be used to help with signs related to benign prostatic hypertrophy, such as an increased urge to urinate, straining to defecate, and blood in the urine. Finasteride is also used to treat adrenal disease in ferrets.

Its use in dogs and ferrets is ‘off-label’. Many drugs are commonly prescribed for off-label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully.

How do I give my pet finasteride?

Finasteride comes in pill form and is given by mouth. It may be given with or without food. If your pet vomits or seems unwell after receiving the medication on an empty stomach, give the next dose with a small amount of food.

Finasteride should be temporarily discontinued prior to and during breeding to minimize any potential issues with offspring.

This medication can take up to a few weeks before full effects are noted, but gradual improvements are usually appreciable after a few days.

What if I miss giving my pet the medication?

Give the missed dose as soon as you remember, and then wait the recommended amount of time between doses; if it is close to the next scheduled dose when you remember, skip the dose you missed and give it at the next scheduled time. After that, return to the regular schedule. Never give your pet two doses at once or give extra doses.

Are there any potential side effects from finasteride?

No side effects have been reported in dogs.

This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this medication?

In dogs: Young/sexually developing dogs should not be given this medication, nor should it be given to sexually mature, pregnant, or nursing females. Finasteride should not be given to dogs that are known to be hypersensitive to it. Use cautiously in dogs with significant liver disease.

In humans: Finasteride is a known teratogen that can be absorbed through the skin, so pregnant or potentially pregnant women must handle this medication with EXTREME CAUTION. Gloves should be worn when handling the medication. DO NOT crush pills, as inhaling the drug is just as dangerous as touching or consuming it – crushing the pills creates powders that can become airborne. If your pet vomits after giving this drug, wear gloves while cleaning up. Women hoping to become pregnant should also avoid the sperm of male partners exposed to finasteride.

"DO NOT crush pills, as inhaling the drug is just as dangerous as touching or consuming it..."

Are there any drug interactions I should be aware of?

No drug interactions with finasteride have been reported. Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this medication?

Prostate exams should be done to determine if the drug is working. If used to treat clinical signs, monitor for relief of symptoms.

How do I store finasteride?

Store in a tightly sealed container, protected from light, at room temperature (below 30°C or 86°F).

What should I do in case of an emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility

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