Sildenafil for Dogs and Cats: Uses, Dosage, and Side Effects

Sildenafil is a prescription medication veterinarians use to treat pulmonary arterial hypertension in dogs and cats. It may also be prescribed for certain other conditions, including megaesophagus and myxomatous mitral valve disease in dogs.

Here’s how sildenafil works, when it’s prescribed, possible side effects, dosing guidance, and important safety information.

What Is Sildenafil?

Sildenafil is a prescription medication used to treat pulmonary arterial hypertension (high blood pressure in the blood vessels of the lungs) in dogs and cats.

Common uses: Veterinarians may prescribe sildenafil to:

• Treat pulmonary arterial hypertension in dogs and cats
• Help improve symptoms associated with megaesophagus in dogs
• Help manage myxomatous mitral valve disease (MMVD) in dogs

FDA approval: Sildenafil is FDA-approved for human use as a generic medication and under the brand names Viagra® and Revatio®.

Although sildenafil is not FDA-approved as a veterinary medication, veterinarians may legally prescribe it extra-label (off-label) when they determine it is appropriate for a pet.

Compounded sildenafil: In some cases, your veterinarian may recommend a compounded formulation when:

• Your pet has difficulty taking the commercially available formulation.
• The required dosage strength is not commercially available.
• Your pet is allergic to an ingredient in the FDA-approved medication.

Compounded medications are not FDA-approved. They are prepared by a veterinarian or licensed pharmacist to meet an individual patient's specific needs.

How Sildenafil Works

Sildenafil works by relaxing and widening the blood vessels in the lungs, making it easier for the heart to pump blood through them.

In dogs with megaesophagus, sildenafil also helps relax the muscle at the lower end of the esophagus, allowing it to widen so food can pass into the stomach more easily.

How To Give Sildenafil

Give sildenafil exactly as directed by your veterinarian.

Administration tips:

• Follow the directions on the prescription label or those provided by your veterinarian.
• Sildenafil is typically given every eight to 12 hours, depending on the condition being treated.
• Give sildenafil on an empty stomach whenever possible.
• If your pet develops vomiting or digestive upset after receiving sildenafil on an empty stomach, contact your veterinarian. They may recommend giving it with a small amount of food.
• If vomiting continues, contact your veterinarian for further guidance.

Missed a Dose?

If you miss a dose of sildenafil, contact your veterinarian for guidance. In many cases, they may recommend giving the missed dose when you remember. 

However, if it is almost time for your pet's next scheduled dose, they may advise skipping the missed dose and resuming the normal dosing schedule.

In most cases, do not give extra or double doses.

Sildenafil Side Effects

Sildenafil is generally well tolerated, but side effects can occur. Most side effects are uncommon and are usually mild.

Possible side effects include:

• Vomiting
• Diarrhea
• Decreased appetite
• A flushed or reddened appearance of the skin, especially around the belly or groin

Human Side Effects

Sildenafil is also an FDA-approved medication for people, but human and veterinary doses, side effects, and drug interactions differ.

If you accidentally ingest sildenafil prescribed for a pet, contact your physician immediately or call the National Poison Control Center at 800-222-1222.

Monitoring Your Pet

Your veterinarian may recommend monitoring or routine testing while your pet is taking sildenafil based on their individual health needs, other medications, and the condition being treated.

When To Call Your Veterinarian

Contact your veterinarian if:

• Your pet develops severe side effects.
• Your pet's condition worsens or does not improve with treatment.
• You suspect your pet has received an overdose.
• You have additional questions or concerns about using sildenafil.

Sildenafil Overdose

A sildenafil overdose can cause dangerously low blood pressure and other serious side effects that require immediate veterinary attention.

Signs of an overdose may include:

• Very low blood pressure
• Weakness
• Vomiting
• High heart rate
• Collapse
• Lethargy

If you suspect your pet has received an overdose, seek emergency veterinary care immediately, contact your veterinarian, or call an animal poison control center. Consultation fees may apply.

• Pet Poison Helpline: (855) 764-7661
• ASPCA Animal Poison Control: (888) 426-4435

How To Store Sildenafil

Store sildenafil according to the product label to help maintain its safety and effectiveness.

Storage instructions:

• Store sildenafil at a controlled room temperature between 67 F and 77 F (19 C–25 C).
• Brief exposure to temperatures between 59 F and 86 F (15 C–30 C) is acceptable.
• Keep the container tightly closed to protect the medication from moisture and light.
• Store compounded formulations according to the instructions provided by the compounding pharmacy.
• Keep out of reach of children and pets.