# Sildenafil: veterinary dose and monograph

> Sildenafil is a veterinary cardiovascular drug. Phosphodiesterase-5 (PDE5) inhibitor used in veterinary cardiology specifically for PULMONARY HYPERTENSION — it selectively dilates the pulmonary vasculature, reduces right-heart afterload and improves exercise tolerance, quality of life… Indications include pulmonary hypertension (pre-capillary/reactive) in dogs — first-line vasodilator; symptom control (syncope, exercise intolerance, cough) in pulmonary hypertension; adjunct in some megaoesophagus cases (relaxes lower oesophageal sphincter). This monograph lists 3 reference doses for dogs and cats, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/sildenafil · Last reviewed: 2026-10-01

## At a glance

- **Drug class:** Cardiovascular
- **Also known as:** Revatio, Viagra, Sildigra, Sildenafil citrate
- **Species with doses:** Dogs and Cats
- **General dose range:** 1–3 mg/kg PO q8–12h — check the species tables for the indication
- **Routes:** PO
- **Last reviewed:** 1 October 2026

## Indications

- Pulmonary hypertension (pre-capillary/reactive) in dogs — first-line vasodilator
- Symptom control (syncope, exercise intolerance, cough) in pulmonary hypertension
- Adjunct in some megaoesophagus cases (relaxes lower oesophageal sphincter)

## Sildenafil dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

### Dogs

*Sildenafil doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Pulmonary hypertension | 1–3 mg/kg | PO | q8–12h | — |
| Megaoesophagus | 1 mg/kg | PO | q12h | — |

- Pulmonary hypertension: Papich 5e: 2 mg/kg q12h PO (interval 8–24 h; up to 3 mg/kg in some dogs). Plumb’s p.1061: median 1.9 mg/kg (0.5–2.7) q8–24h (Bach 2006); 0.5–1 mg/kg twice daily, up to 2–3 mg/kg three times daily (Tilley 2007); 1–2 mg/kg three times daily (Oyama 2009).
- Megaoesophagus: Papich 5e: 1 mg/kg PO q12h.

### Cats

*Sildenafil doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Pulmonary hypertension (uncommon) | 1 mg/kg | PO | q8h | — |

- Pulmonary hypertension (uncommon): Papich 5e and Plumb’s p.1061 (Henik 2007): 1 mg/kg PO q8h.

## Contraindications

Concurrent nitrates / nitric-oxide donors (catastrophic hypotension). Severe systemic hypotension or hypovolaemia. Caution in left-sided CHF without controlled congestion (can worsen pulmonary oedema by increasing pulmonary blood flow). Known hypersensitivity. Use cautiously with other vasodilators/PDE inhibitors.

## Species-specific warnings

> **Caution:** Cats: Limited feline data — reserve for documented pulmonary hypertension and dose conservatively with monitoring.

## Adverse effects

- Systemic hypotension, weakness, lethargy
- Cutaneous flushing, nasal congestion
- GI upset
- Worsening pulmonary oedema if left-sided congestion is uncontrolled
- Rare: tachycardia

## Drug interactions

- Nitrates / nitroprusside / NO donors: severe, potentially fatal hypotension — contraindicated
- Other vasodilators / antihypertensives: additive hypotension
- CYP3A4 inhibitors (ketoconazole, erythromycin, itraconazole): increased sildenafil levels
- Alpha-blockers: additive hypotension

## Pregnancy and lactation

Limited veterinary data; use only if clearly needed. (In human medicine it has both been studied and cautioned in pregnancy.)

## Monitoring

- Clinical response (syncope, exercise tolerance, respiratory effort, cough)
- Echocardiographic estimate of pulmonary artery pressure (tricuspid regurgitation velocity) to guide titration
- Systemic blood pressure
- Signs of left-sided congestion/pulmonary oedema if relevant

## Toxicity and overdose

Overdose: pronounced systemic hypotension, tachycardia, flushing, and weakness/collapse. Generally non-fatal with supportive care unless combined with nitrates. Priapism is a theoretical effect.

Management: No specific antidote. IV fluids and, if needed, vasopressors for hypotension; supportive monitoring of blood pressure and heart rate. Avoid any nitrate co-administration. Effects abate as the drug is cleared.

## Clinical pearls

- The first-line drug for canine pulmonary hypertension — often transforms quality of life (less syncope, better exercise tolerance)
- Titrate against echo-estimated PA pressure and clinical signs, not a fixed dose
- Absolutely avoid with any nitrate — the combination can be fatal
- If there is concurrent left heart failure, control congestion first; unopposed pulmonary vasodilation can flood the lungs
- Human Revatio/Viagra/Sildigra tablets are commonly used (and compounded) for dogs in practice

## Mechanism of action

Inhibits phosphodiesterase type 5, the enzyme that degrades cyclic GMP. By preserving cGMP in vascular smooth muscle — abundant in the pulmonary vasculature — it enhances nitric-oxide-mediated vasodilation, preferentially lowering pulmonary arterial pressure and resistance with comparatively modest systemic effect. Increased cGMP also relaxes some other smooth muscle (e.g. lower oesophageal sphincter).

## Formulations and products

- 20 mg tablet (Revatio)
- 25 mg tablet
- 50 mg tablet
- Oral suspension 10 mg/mL (compounded)
- Revatio — 20 mg tablet, Tablet (human-label)
- Sildigra / Penegra — 25 / 50 / 100 mg tablet, Tablet (human-label)

## Storage

Tablets: 15–30 °C, dry, protected from light. Compounded suspension: refrigerate and use within the assigned beyond-use date.

## Before you use this dose

> **Caution:** Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

## Other cardiovascular drugs

- [Procainamide](https://vetmasterji.com/drugs/procainamide)
- [Propranolol](https://vetmasterji.com/drugs/propranolol)
- [Quinidine](https://vetmasterji.com/drugs/quinidine)
- [Ramipril](https://vetmasterji.com/drugs/ramipril)
- [Sodium Nitroprusside](https://vetmasterji.com/drugs/nitroprusside)
- [Sotalol](https://vetmasterji.com/drugs/sotalol)
- [Telmisartan](https://vetmasterji.com/drugs/telmisartan)
- [Vasopressin (Arginine Vasopressin)](https://vetmasterji.com/drugs/vasopressin)

## Frequently asked questions

### What is the dose of Sildenafil for dogs?

Reference doses for Sildenafil in dogs: 1–3 mg/kg PO q8–12h (Pulmonary hypertension); 1 mg/kg PO q12h (Megaoesophagus). Confirm against the label and the patient before use.

### What is the dose of Sildenafil for cats?

Reference doses for Sildenafil in cats: 1 mg/kg PO q8h (Pulmonary hypertension (uncommon)). Confirm against the label and the patient before use.

### When should Sildenafil not be used?

Concurrent nitrates / nitric-oxide donors (catastrophic hypotension). Severe systemic hypotension or hypovolaemia. Caution in left-sided CHF without controlled congestion (can worsen pulmonary oedema by increasing pulmonary blood flow). Known hypersensitivity. Use cautiously with other vasodilators/PDE inhibitors.

### What are the side effects of Sildenafil in animals?

Systemic hypotension, weakness, lethargy; Cutaneous flushing, nasal congestion; GI upset; Worsening pulmonary oedema if left-sided congestion is uncontrolled; Rare: tachycardia.

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.