Dog Health
Sildenafil (Viagra) for Dogs: A Medication to Lower Blood Pressure in the Lungs
Key takeaways:
Sildenafil (Viagra) is a medication used in dogs to lower blood pressure in the lungs and treat megaesophagus, a condition that leads to difficulty swallowing.
Sildenafil is generally safe for most dogs, but it can cause low blood pressure if used improperly. It should only be given to a dog under the direct supervision of a licensed veterinarian.
Use of sildenafil in dogs is considered “off-label,” which means that the medication is not FDA approved as a treatment for dogs.
Viagra is a well-known erectile dysfunction treatment for humans. Sildenafil, the active ingredient in Viagra, is also used in humans to treat pulmonary hypertension. Pulmonary hypertension is a condition that leads to high blood pressure in the lungs.
But what about sildenafil for dogs? It turns out that there are veterinary uses for sildenafil as a treatment for specific disorders in dogs.
Common names | Sildenafil (Viagra, Revatio) |
What it treats | Megaesophagus, pulmonary arterial hypertension |
How it comes (forms) | Tablets, liquid suspension, injection |
Common side effects | Stomach upset Reduced appetite Vomiting Diarrhea Skin flushing |
Average cost | $10-$21 for a 30-day supply of pills |
Sildenafil belongs to a class of medications called phosphodiesterase (PDE) inhibitors. These medications help dilate (expand) blood vessels and relax muscles in the body. Specifically, sildenafil is a PDE5 inhibitor that targets cells in the lungs and penis.
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PDE inhibitors work by blocking the enzyme phosphodiesterase. This helps decrease the level of calcium inside your dog’s cells, resulting in benefits for certain conditions.
In dogs, sildenafil is primarily prescribed for two conditions:
Pulmonary hypertension
Megaesophagus
As mentioned, sildenafil targets blood vessels in the lungs. The medication has been effectively used in dogs to treat pulmonary hypertension. Pulmonary hypertension is a life-threatening condition that occurs when blood pressure is too high in a dog’s lungs.
Pulmonary hypertension is usually the result of another health condition, such as heart disease. Therefore, treatment is aimed at lowering blood pressure in the lungs and managing the underlying condition, if possible.
Sildenafil is the only blood pressure medication thought to be effective at treating pulmonary hypertension in dogs. Other blood pressure medications do not specifically target blood vessels in the lungs, like sildenafil does. And, in some cases, these medications may make the problem worse.
At the moment, there are few studies that demonstrate sildenafil’s ability to actually lower blood pressure. And some studies suggest sildenafil doesn’t help with pulmonary hypertension as much as researchers originally hoped. Despite this, several studies have found that dogs with pulmonary hypertension who take sildenafil have a higher quality of life.
Sildenafil was also recently shown to be a promising treatment for canine megaesophagus. Canine megaesophagus is a rare condition in dogs that affects the esophagus, the tube that connects the mouth to the stomach. The condition causes the esophagus to widen, which makes it difficult for food to move to the stomach. This causes dogs to regurgitate food, making them more prone to:
Aspiration pneumonia
Weight loss
Wasting (becoming weak or emaciated)
Poor quality of life
Historically, there hasn’t been a medication that has been helpful for dogs with megaesophagus. But sildenafil seems to help this difficult-to-manage condition.
Sildenafil is available in 10 mg, 20 mg, 25 mg, and 100 mg tablets. It can also be compounded into a liquid. An injectable form of sildenafil is available for use in veterinary clinics.
The standard dosage of sildenafil for pulmonary hypertension in dogs ranges from 0.5 mg to 3 mg per kg of body weight every 8 to 24 hours. The dosage of sildenafil for megaesophagus is 1 mg per kg of a dog’s body weight every 12 hours.
Sildenafil for dogs should be given on an empty stomach at least 1 hour before feeding or 2 hours after feeding. And the medication typically takes effect within 1 to 2 hours.
If your dog has been prescribed sildenafil in a liquid form, shake well before use, if indicated. Measure your dog’s dose carefully, and follow all instructions about giving them the medication and storing it.
Use of sildenafil in dogs is considered “off-label” or “extra-label.” This means that sildenafil is not FDA approved for use in dogs. But there are many medications that are prescribed off-label safely and effectively for dogs.
Sildenafil is generally safe for most dogs and doesn’t cause too many side effects. The most common reported side effects in dogs include:
Skin flushing
Decreased appetite
Vomiting
Diarrhea
If your dog vomits when you give them sildenafil on an empty stomach, give them their future doses with food. If they’re still vomiting after taking the medication, call your veterinarian for additional advice.
Sildenafil is a short-acting medication that stops working within 24 hours for most dogs. However, the effects of sildenafil may last longer in dogs with liver or kidney disease.
The most serious side effect associated with sildenafil in dogs is low blood pressure. This is rare, but it can happen. Therefore, sildenafil should not be given to dogs that also take medication for high blood pressure, including nitrate medications.
In addition, sildenafil should be used with caution in dogs who have:
Heart disease
Low blood pressure
Dehydration
Bleeding disorders
Experts don’t know if sildenafil is safe for dogs that are pregnant or nursing. So it may be best to avoid giving the medication to pregnant or nursing dogs.
The following medications are known to have interactions with sildenafil:
Medications for heart disease, kidney disease, and high blood pressure
Antifungal medications that end in “-azole,”such as ketoconazole
Fluoroquinolone antibiotics, such as ciprofloxacin
Macrolide antibiotics, such as clarithromycin and erythromycin
Rifampin
Seizure medications, such as phenobarbital
Chemotherapy medications, such as paclitaxel
Be sure to tell your veterinarian about any medications that your dog takes before giving your dog sildenafil. This includes letting your vet know if your dog takes any vitamins, supplements, or herbs.
If your dog misses a dose of sildenafil, give them the dose as soon as you remember. Then, wait the prescribed amount of time between doses after that.
In other words, if you give your dog sildenafil every 12 hours, wait 12 hours from the time you gave them the missed dose until their next one. Never give your dog two doses of the medication at the same time.
Sildenafil (Viagra) is used to treat lower blood pressure in the lungs and megaesophagus in dogs. Sildenafil is generally safe and well tolerated by most dogs. Use of sildenafil in dogs is considered “off-label” and should only be done under the direct supervision of a licensed veterinarian.
British Small Animal Veterinary Association. (2014). Sildenafil.
Brown, A. J., et al. (2010). Clinical efficacy of sildenafil in treatment of pulmonary arterial hypertension in dogs. Journal of Veterinary Internal Medicine.
Häggström, J. (2017). Diagnosis and management of pulmonary hypertension in dogs. World Small Animal Veterinary Association Congress Proceedings.
Johnson, L. R., et al. (2019). Clinical features and outcome in 25 dogs with respiratory-associated pulmonary hypertension treated with sildenafil. Journal of Veterinary Internal Medicine.
Kellum, H. B., et al. (2007). Sildenafil citrate therapy in 22 dogs with pulmonary hypertension. Journal of Veterinary Internal Medicine.
Mehain, S. O., et al. (2022). A randomized crossover study of compounded liquid sildenafil for treatment of generalized megaesophagus in dogs. American Journal of Veterinary Research.
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