Home/Medicines/Sildenafil

Sildenafil

Prescription

Phosphodiesterase-5 (PDE5) inhibitor

Last reviewed 19 Apr 2026 · PetCare.AI Editorial Team

Species

Dog, Cat

Brands

3 available

Interactions

2 documented

Formulations

Mechanism of action

Selectively inhibits PDE5, increasing cGMP levels in pulmonary vascular smooth muscle, causing vasodilation and reducing pulmonary arterial pressure

At a glance

Class

Phosphodiesterase-5 (PDE5) inhibitor

Schedule

Prescription

Storage

Store below 30°C, protect from moisture

Dosing

🐕

Dog

Pulmonary hypertension

Dose

1–3 mg/kg

Route

Frequency

BID to TID

Max dose

75 mg/dose; 225 mg/day

Duration: Long-term

🐈

Cat

Pulmonary hypertension

Dose

1–2 mg/kg

Route

Frequency

BID to TID

Max dose

10 mg/dose; 30 mg/day

Duration: Long-term

Educational reference only

This information is provided for educational purposes and is not a substitute for professional veterinary advice, diagnosis, or treatment. Always consult a qualified veterinarian before administering any medication to your pet. Find a vet near you →

Formulations

💊

Tablet — 3

Strength

25mg

Available in India

Strength

50mg

Available in India

Strength

100mg

Available in India

Storage

Store below 30°C, protect from moisture

Safety

Absolute contraindications — do not use

Concurrent nitrate therapy
Severe hypotension risk
Nitroglycerin

Use with caution

Systemic hypotension
May worsen

Adverse effects

Common

Facial flushing

GI upset

Nasal congestion

Serious

Systemic hypotension

Priapism (rare)

Monitoring parameters

Blood pressureHeart rateExercise toleranceEchocardiography for pulmonary pressures

Educational reference only

Interactions

Contraindicated — 1

Nitroglycerin (Transdermal)

contraindicated

Sildenafil + nitrate: synergistic cGMP-mediated vasodilation causing severe, potentially fatal hypotension.

Management: NEVER combine. Allow 24h washout of sildenafil before nitrate.

Moderate — 1

Amlodipine

moderate

Additive vasodilation and hypotension; both lower blood pressure via different mechanisms

Management: Monitor blood pressure. May need to reduce amlodipine dose.

Educational reference only

Brands

International

Viagra

Pfizer

India

Penegra

Zydus

Manforce

Mankind

FAQs

Frequently asked questions

›What is Sildenafil?

Sildenafil is a phosphodiesterase-5 (pde5) inhibitor used in pets. Selectively inhibits PDE5, increasing cGMP levels in pulmonary vascular smooth muscle, causing vasodilation and reducing pulmonary arterial pressure

›What is Sildenafil used for in pets?

Sildenafil is used in veterinary medicine for: Pulmonary hypertension.

›What is the Sildenafil dose for dogs?

For dogs, Sildenafil is typically dosed as follows — Pulmonary hypertension: 1–3 mg/kg PO BID to TID. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.

›What is the Sildenafil dose for cats?

For cats, Sildenafil is typically dosed as follows — Pulmonary hypertension: 1–2 mg/kg PO BID to TID. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.

›What are the side effects of Sildenafil?

Common: Facial flushing, GI upset, Nasal congestion. Serious (call your vet immediately): Systemic hypotension, Priapism (rare).

›Does Sildenafil need a prescription?

Yes. Sildenafil is a prescription medication and should only be administered under veterinary supervision.

›When should Sildenafil not be used?

Do not use Sildenafil if: Concurrent nitrate therapy.

Educational reference only

References

The PetCare.AI drug reference is built from 13 authoritative sources cited across 580 drug monographs.

Textbooks & handbooks — 5

Plumb's Veterinary Drug Handbook
Withrow & MacEwen's Small Animal Clinical Oncology
Merck Veterinary Manual
NRC Nutrient Requirements of Dogs and Cats
Veterinary Pharmacology and Therapeutics (Riviere & Papich)

Clinical guidelines & consensus — 4

ASPCA Animal Poison Control Center Guidelines
AAHA Diabetes Management Guidelines
ASPCA Poison Control Guidelines
RECOVER CPR Guidelines

Journals & peer-reviewed studies — 2

EPIC Study (J Vet Intern Med 2016)
JVIM FAT CAT Study

Regulatory & approvals — 1

CDSCO Veterinary Drug Approval Registry (1969–2026)

Databases — 1

Washington State University VCPL MDR1 Database

Related medicines

Other medicines in the same class (Phosphodiesterase-5).

Tadalafil

Selectively inhibits PDE5, preventing cGMP degradation in pulmonary vascular smooth muscle. Increased cGMP causes vasodilation, reducing pulmonary artery pressure. Longer half-life than sildenafil (17h vs 4h) — allows once-daily dosing.

dogcat