Sildenafil for Dogs – Pulmonary Hypertension
Sildenafil (Viagra/Revatio) is a PDE5 inhibitor used for pulmonary hypertension in dogs.
Dose
1-3 mg/kg PO every 8-12 hours (TID-BID)
Dose Reference Table
| Weight | Range |
|---|---|
| 5 kg | 5-15 mg |
| 10 kg | 10-30 mg |
| 15 kg | 15-45 mg |
| 20 kg | 20-60 mg |
| 30 kg | 30-90 mg |
| 40 kg | 40-120 mg |
Tablet sizes: 20 mg (Revatio), 25/50/100 mg (Viagra). Compounded liquid for small dogs.
Mechanism
Blocks PDE5 → increased cGMP in pulmonary vasculature → pulmonary vasodilation → reduced pulmonary arterial pressure + improved oxygenation + exercise tolerance.
Indications
Primary
- Pulmonary hypertension secondary to:
- MVD (mitral valve disease)
- DCM
- Heartworm disease
- Chronic pulmonary disease
- Eisenmenger (PDA reverse)
Off-Label
- Megaesophagus (LES relaxation)
- Refractory CHF adjunct
PH Signs to Watch
- Syncope (fainting)
- Exercise intolerance
- Respiratory distress
- Cyanosis
- Right-sided CHF (ascites)
- Cough
Diagnosed by echocardiography.
âš Contraindications
- NITRATES (nitroglycerin, isosorbide) – severe hypotension/collapse
- Severe hypotension
- Hypersensitivity
Drug Interactions
- Alpha-blockers (tamsulosin, prazosin) – additive hypotension
- ACE-i + diuretics – additive hypotension
- CYP3A4 inhibitors (ketoconazole, erythromycin) – increase levels
- Rifampin – decreases levels
Side Effects
- Hypotension
- Flushing
- GI upset
- Visual changes (rare)
- Priapism (very rare in dogs)
Frequently Asked Questions
How much sildenafil for my dog with pulmonary hypertension?
STANDARD DOSE: 1-3 mg/kg PO every 8-12 hours (TID-BID). EXAMPLES: 1) 5 kg = 5-15 mg; 2) 10 kg = 10-30 mg; 3) 15 kg = 15-45 mg; 4) 20 kg = 20-60 mg; 5) 30 kg = 30-90 mg; 6) 40 kg = 40-120 mg. TABLETS: 20 mg Revatio (PH approved), 25/50/100 mg Viagra generic; compounded liquid for very small dogs. Start lower end if borderline hypotension or on ACE-i + diuretic. Increase based on clinical response + echocardiographic monitoring. With or without food. Once started, continue lifelong typically. AVOID NITRATES (severe hypotension).
What is sildenafil used for in dogs?
Primarily PULMONARY HYPERTENSION (PH) – elevated blood pressure in pulmonary arteries. CAUSES: 1) MVD (mitral valve disease) – left-sided heart failure increases pulmonary venous pressure; 2) DCM dilated cardiomyopathy; 3) HEARTWORM disease – mechanical obstruction; 4) CHRONIC PULMONARY DISEASE (chronic bronchitis, pulmonary fibrosis); 5) Reverse PDA (Eisenmenger); 6) Idiopathic. SIGNS: syncope, exercise intolerance, respiratory distress, cyanosis, right-sided CHF (ascites). DIAGNOSED by ECHOCARDIOGRAM (tricuspid regurgitation jet velocity to estimate PA pressure). SILDENAFIL benefits: reduces PA pressure, improves exercise tolerance, reduces syncope, prolongs survival. Also off-label for MEGAESOPHAGUS (lower esophageal sphincter relaxation). Continue alongside CHF medications (furosemide, pimobendan, ACE-i).
Can my dog take sildenafil with heart failure medications?
YES – commonly combined. STANDARD CHF + PH protocol: 1) FUROSEMIDE (diuretic); 2) PIMOBENDAN (inodilator); 3) ACE-i (benazepril/enalapril); 4) SPIRONOLACTONE (K+-sparing); 5) SILDENAFIL added for PH component. SAFE combinations. MONITOR: 1) Blood pressure (additive hypotension possible); 2) Renal values (ACE-i + diuretic); 3) Electrolytes (K+); 4) Hydration status; 5) Sleeping respiratory rate (CHF); 6) Echocardiographic PH; 7) Exercise tolerance. CONTRAINDICATIONS: 1) NITRATES (nitroglycerin) – severe hypotension; 2) Alpha-blockers (tamsulosin) – additive; 3) Severe baseline hypotension. WORK WITH CARDIOLOGIST for complex multi-drug CHF/PH management. Excellent quality-of-life benefit possible.
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References & Further Reading
The dosing ranges and safety information on this page are drawn from the following veterinary references. Always defer to your own veterinarian and the manufacturer’s label for your specific product.
- Plumb DC. Sildenafil.
- Bach JF et al. Sildenafil for canine pulmonary hypertension. JVIM.
- Kellihan HB. Pulmonary hypertension in dogs.
- Brown AJ et al. Pulmonary hypertension – clinical management.
- PuppaDogs. Pulmonary Hypertension Calculator, MVD ACVIM Stage Calculator. puppadogs.com.
