sildenafil
Sildenafil (Viagra) is a phosphodiesterase 5 (PDE5) blocker that veterinarians prescribe off-label to treat pulmonary hypertension (high blood pressure in the lungs) in dogs and cats. In dogs, it’s also used to help manage megaesophagus, a condition where the esophagus becomes abnormally large. This medication is commercially available as a tablet, liquid, and injection. It’s typically given two or three times a day. Common side effects include diarrhea, vomiting, and reduced appetite.
What is Sildenafil for pets?
What is Sildenafil for pets used for?
Pulmonary hypertension (high blood pressure in the lungs) in dogs and cats
Megaesophagus in dogs
How Sildenafil for pets works
Sildenafil is a phosphodiesterase 5 (PDE5) blocker, which means it blocks an enzyme called PDE-5 found in certain parts of the body. It works by relaxing smooth muscle, including in the blood vessels of the lungs and the muscles in the esophagus.
Because of this, it helps lower blood pressure in the lungs, making it useful for treating pulmonary hypertension. In dogs with megaesophagus, the medication helps by relaxing the esophagus, making it easier for them to eat and swallow food.
Drug Facts
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What are the side effects of Sildenafil for pets?
Common Side Effects
- Skin flushing
- Reduced appetite
- Vomiting
- Diarrhea
Other Side Effects
- Tiredness
- Weakness
- Low blood pressure
The following side effects have also been reported
Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.
Check with your doctor immediately if any of the following side effects occur:
Less common
Bladder pain
burning feeling in the chest or stomach
burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings
cloudy or bloody urine
dizziness
increased frequency of urination
indigestion
pain on urination
stomach upset
tenderness in the stomach area
Rare
Abnormal vision
behavior change similar to drunkenness
bleeding of the eye
blurred vision
bone pain
breast enlargement
chills
cold sweats
confusion
convulsions (seizures)
cool and pale skin
deafness or hearing loss
decrease in amount of urine or the frequency of urination
decreased vision
difficulty in concentrating
dizziness or lightheadedness, especially when getting up suddenly from a lying or sitting position
double vision
drowsiness
dryness, redness, scaling, or peeling of the skin
excessive hunger
fainting or faintness
fast, irregular, or pounding heartbeat
feeling of something in the eye
fever or chills
headache (severe or continuing)
increase in the size of the pupil
increased sweating
increased thirst
lower back or side pain
migraine headache
nausea (severe or continuing)
nervousness
nightmares
numbness of the hands
painful, swollen joints
prolonged, painful erection of penis
redness, burning, or swelling of the eyes
redness, itching, or tearing of the eyes
restless sleep
seeing shades of colors differently than before
sensitivity to light
shakiness
skin lesions with swelling
skin paleness
skin ulcers
slurred speech
sudden weakness
swelling of the face, hands, feet, or lower legs
trouble breathing
twitching of the muscles
unusual feeling of burning or stinging of the skin
unusual tiredness or weakness
vision changes
vision loss, temporary
Incidence not known
Blindness
Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:
More common
Aches or pains in the muscles
bloody nose
difficult or labored breathing
flushing
headache
pain or tenderness around the eyes and cheekbones
redness of the skin
stomach discomfort following meals
stuffy or runny nose
trouble sleeping
unusually warm skin
Rare
Abdominal or stomach pain
abnormal dreams
clumsiness or unsteadiness
diarrhea or stomach cramps (severe or continuing)
difficulty in swallowing
ear pain
increased amount of saliva
increased skin sensitivity
lack of coordination
loss of bladder control
mental depression
numbness or tingling of the hands, legs, or feet
rectal bleeding
redness or irritation of the tongue
redness, soreness, swelling, or bleeding of the gums
ringing or buzzing in the ears
sensation of motion, usually whirling, either of one's self or of one's surroundings
sexual problems in men (continuing), including failure to experience a sexual orgasm
sleepiness
sores in the mouth and on the lips
tense muscles
trembling and shaking
vomiting
waking to urinate at night
worsening of asthma
Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.
Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.
Pros and cons of Sildenafil for pets
Pros
Helps to improve symptoms and energy in dogs with pulmonary hypertension
One of the few medications that treat megaesophagus in dogs
Can be compounded into a liquid
Cons
Must be given two or three times per day
Common side effects are diarrhea and vomiting
Doesn’t cure the underlying medical condition
Pharmacist tips for Sildenafil for pets
Sildenafil can be given with food to make it easier for your pet to take. If your pet won’t eat it, you can also try placing the tablet on their tongue and gently holding their mouth closed until it dissolves.
Sildenafil can be compounded into a liquid form. Follow your pharmacist’s instructions on how to store it and when it expires. Always use a medication syringe or dosing tool (not a household spoon) to make sure your pet gets the correct dose.
Sildenafil is often used with other medications. Tell your vet and pharmacist about all medications and supplements your pet takes to make sure they're safe to use together.
It isn’t known if sildenafil is safe for pregnant animals. It should only be given if the benefits outweigh the risks. Talk to a vet before giving this medication to your pet if they’re pregnant.
The dose of sildenafil depends partly on how your pet responds to it. Keep your vet updated on how it’s working so they can adjust the dose if needed.
Frequently asked questions about Sildenafil for pets
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What are the risks and warnings for Sildenafil for pets?
Sildenafil can cause some serious health issues. This risk might be even higher for certain pets. If this worries you, talk to your veterinarian about other options.
Low blood pressure
Risk factors: Taking with other medications that lower blood pressure
Sildenafil can cause low blood pressure in pets, especially if they’re taking other medications that affect blood pressure. It shouldn’t be given with nitrate medications as this can cause a dangerous drop in blood pressure. Watch for symptoms like weakness, fainting, shaking, or trouble standing. If you notice any of these signs, contact your veterinarian right away.
Sildenafil dosage forms
Typical dosing for Sildenafil for pets
The dose is based on your pet’s weight and medical condition.
Dogs:
Pulmonary hypertension: The typical dose is 1 mg/kg to 3 mg/kg by mouth every 8 to 12 hours.
Megaesophagus: The typical dose is 1 mg/kg by mouth every 12 hours.
Cats:
Pulmonary hypertension: The typical dose is 1 mg/kg to 2 mg/kg a day by mouth every 12 hours.
Interactions between Sildenafil and other drugs for pets
Using this medicine with any of the following medicines is not recommended. Your doctor may decide not to treat you with this medication or change some of the other medicines you take.
- Amprenavir
- Amyl Nitrite
- Atazanavir
- Boceprevir
- Cobicistat
- Darunavir
- Erythrityl Tetranitrate
- Fosamprenavir
- Indinavir
- Isosorbide Dinitrate
- Isosorbide Mononitrate
- Lopinavir
- Molsidomine
- Nelfinavir
- Nitroglycerin
- Nitroprusside
- Pentaerythritol Tetranitrate
- Propatyl Nitrate
- Riociguat
- Ritonavir
- Saquinavir
- Telaprevir
- Tipranavir
Using this medicine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Cannabis
- Ceritinib
- Clarithromycin
- Conivaptan
- Dihydrocodeine
- Duvelisib
- Fluconazole
- Fosnetupitant
- Idelalisib
- Itraconazole
- Ivosidenib
- Larotrectinib
- Lefamulin
- Lorlatinib
- Lumacaftor
- Nefazodone
- Netupitant
- Simeprevir
- Telithromycin
- Voriconazole
Using this medicine with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Alfuzosin
- Bosentan
- Bunazosin
- Ciprofloxacin
- Delavirdine
- Doxazosin
- Erythromycin
- Etravirine
- Ketoconazole
- Moxisylyte
- Nebivolol
- Prazosin
- Rifapentine
- Silodosin
- Tamsulosin
- Terazosin
- Trimazosin
How much does Sildenafil cost?
Sildenafil contraindications for pets
Pets taking nitrate medications
What are alternatives to Sildenafil for pets?
Pulmonary hypertension (high blood pressure in the lungs) in dogs and cats
Megaesophagus in dogs
Congestive heart failure (CHF) in dogs and cats
High blood pressure in dogs and cats
Kidney problems in dogs and cats
Sildenafil images
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References
Best studies we foundBritish Small Veterinary Association. (2017). Sildenafil.
Gordon, S. G., et al. (2024). Vasoactive drugs for use in animals. Merck Manual Veterinary Manual.
Häggström, J. (2017). Diagnosis and management of pulmonary hypertension in dogs. World Small Animal Veterinary Association Congress Proceedings, 2017.
Huynh, J., et al. (2024). A retrospective study of sildenafil administration in 55 cats with cardiopulmonary disease (2009-2021). Animals.
Kittleson, M. D. (2024). Systemic and pulmonary hypertension dogs and cats. Merck Manual Veterinary Manual.
Reinero, C., et al. (2020). ACVIM consensus statement guidelines for the diagnosis, classification, treatment, and monitoring of pulmonary hypertension in dogs. Journal of Veterinary Internal Medicine.
Saetang, K., et al. (2020). Short-term effects of sildenafil in the treatment of dogs with pulmonary hypertension secondary to degenerative mitral valve disease. Veterinary World.
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