Medicated

Viagra for Dogs: An Unusual Choice of Treatment


written by Dr.Jo De Klerk - Mar 1, 2021
medically reviewed by Dr. Christine Bishara, MD - Sep 7, 2021

Photo Credit: by Mikhail Tsypkin, flickr.com
Photo Credit: by Mikhail Tsypkin, flickr.com

For many ailments, dogs can be prescribed human medications to treat or manage their condition. This is known as “off-licence” or “extra-label” prescribing, as the medication is not licenced for use in animals by the FDA. On many occasions, off-licence medications are used for similar ailments as their use in humans, but this is not always the case. Viagra, for example, is a classic example.

Viagra may seem an unusual choice of treatment, however it is remarkably effective at improving the quality of life in dogs with a certain heart and lung condition: pulmonary hypertension.

What is Viagra?

It may come as a surprise to see Viagra as a treatment choice for dogs. In humans, it is typically used to treat erectile dysfunction, however, in dogs this is not a condition of concern.

The active ingredient, Sildenafil, can be used in dogs where there is an increased pressure in the lung blood vessels. This is known as pulmonary hypertension. Viagra, and the generic form Sildenafil, is available in 25mg, 50mg or 100mg sized tablets.

What is pulmonary hypertension in dogs?

Pulmonary hypertension is a condition in which increased blood pressure in the lungs causes the right side of the heart to be put under increased pressure. Typically, dogs with pulmonary hypertension are middle aged or older, or small breed dogs. The most common symptoms are cough, breathing difficulties and loss of consciousness. In more severe cases, a heart murmur, blue discolouration of the lungs and build-up of fluid in the abdomen may also be present.

How does Viagra treat pulmonary hypertension in dogs?

Sildenafil is a drug known as a phosphodiesterase type V inhibitor. It affects a substance known as cGMP, which is found in the vessels in the lungs. Inhibiting phosphodiesterase V increases the amount of cGMP present, which in turn causes smooth muscle relaxation. Smooth muscle is found in the walls of blood vessels, particularly arteries and arterioles, and when the smooth muscle relaxes, the blood vessels dilate. This in turn leads to a decrease in blood pressure.

Pulmonary hypertension is a condition with a poor prognosis. The median survival time is 91 days, however, treatment with Sildenafil can significantly improve quality of life, energy and length of survival.

How to give Viagra to dogs?

Viagra, or any other form of Sildenafil, is not licenced for dogs, and therefore there is not a standard dose or dosing regimen. Your veterinarian will prescribe a dose and course duration which is appropriate for your individual dog, and it is important to follow this accurately. Do not cease giving your dog Sildenafil unless directed by your veterinarian.

Viagra tablets are usually administered orally, however research suggests that it also has an effect when administered rectally, although this is not the preferred route.

To give the tablet orally, place it in a small amount of strong-smelling food that your dog likes. If your dog will not eat the tablet willingly, you can carefully place the tablet at the back of your dog’s tongue and gently hold his mouth shut until he swallows. It’s important that fresh water is always available to help wash down the tablet.

After giving your dog the medication, ensure you thoroughly wash your hands to prevent any of the medication being absorbed by your skin.

The onset of action of sildenafil is approximately 30-60 minutes after administration.

Sildenafil should be stored at room temperature, away from sight and reach of children and animals.

Does Viagra interact with other medications in dogs?

It is important to make your veterinarian aware if your dog is receiving other medications, as sildenafil can interact with certain drugs.

Any drugs which lower the blood pressure should not be taken with sildenafil, which include nitrates, alpha-adrenergic blockers (e.g., phentolamine, phenoxybenzamine, phenothiazines) and calcium-channel blockers (e.g., amlodipine and diltiazem).

In addition to this, sildenafil is known to also interact with cimetidine, erythromycin, itraconazole, phenobarbital (phenobarbitone), clarithromycin and rifampin.

Side effects of Viagra for dogs

Because sildenafil is off-licence for dogs, the side effects have not been fully documented. However, in humans, it may cause vomiting, nasal congestion, breathing difficulties, dizziness, priapism and headaches.

It is assumed dogs may experience some of these symptoms also, however, they may go undetected. The most commonly noticed side effects in dogs have been gastrointestinal upsets and reddening of the skin, and less commonly, a prolonged erection.

If your dog is experiencing any side effects, you should contact your veterinarian immediately for advice.

What to do in a case of an overdose of Viagra in dogs?

If your dog has accidentally consumed higher than the prescribed dose of sildenafil, you should immediately take him to your local vet.

An overdose of sildenafil can cause tachycardia (a high heart rate) which can cause changes in blood pressure, and increased stress on the cardiorespiratory system which is being treated.

To prevent overdoses of sildenafil, ensure the medication is stored somewhere that your dog cannot access it, and that the doses are given at exactly the same times every day. If you miss a dose, do not give a double dose to make up for it. It is important not to exceed the total prescribed dose within a 24-hour timeframe.

Where can you buy Viagra for dogs?

If your pet needs Viagra, for which your veterinarian has provided a prescription, you can order their medication from Canada Pharmacy Online. We are a certified and trusted online pharmacy, which provides high quality medications at competitive and affordable prices.

References

1. Bach JF, Rozanski EA, MacGregor J, Betkowski JM, Rush JE. Retrospective evaluation of sildenafil citrate as a therapy for pulmonary hypertension in dogs. J Vet Intern Med 20(5):1132-5. Available at: https://pubmed.ncbi.nlm.nih.gov/17063705/

2. Yang, HJ, Oh, YI, Jeong, JW, 2018. Comparative single-dose pharmacokinetics of sildenafil after oral and rectal administration in healthy beagle dogs. BMC Vet Res 14: 291. Available at: https://bmcvetres.biomedcentral.com/articles/10.1186/s12917-018-1617-7

3. Wells B, Wright S, 2017. Sildenafil Exposure in a dog. Today’s Veterinary Nurse. Available at: https://todaysveterinarynurse.com/articles/sildenafil-exposure-in-a-dog/

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Dr Jo de Klerk is a veterinarian and a writer. She works with all species and enjoys writing articles for websites and journals. In her spare time she likes to horse ride and spend time with her young family.


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