Sildenafil for Dogs and Cats
Commonly prescribed for: Heart and/or lung problems that cause increased blood pressure in the arteries of the lungs
Species: Dogs and Cats
Therapeutic Class: Phosphodiesterase (PDE) Inhibitor
General Drug Information and Indications
Sildenafil is a drug that is used in dogs and cats with heart and/or lung problems that cause increased blood pressure in the arteries of the lungs. 
Pulmonary hypertension refers to abnormally high blood pressure in the arteries of the lungs that forces the right side of the heart to work harder than normal. Sildenafil causes the smooth muscle surrounding small blood vessels in the lungs to relax, decreasing the work load on the heart. Although there are other similar drugs available on the human market, sildenafil has been the most studied in veterinary medicine.
Sildenafil has been shown to improve energy, exercise tolerance, and overall quality of life in animals with pulmonary hypertension. Research in humans shows that maximum relaxation of the small blood vessels in the lungs occurs 60 minutes after oral administration of sildenafil. Like many other drugs in veterinary medicine, this drug is not FDA approved for use in animals and is not available from a veterinary pharmaceutical manufacturer. Instead, it is compounded by a specialty pharmacy.
How to Give this Medication
Give this medication to your pet exactly as your veterinarian prescribes. If you miss giving your pet a dose of sildenafil, give the next dose as soon as you remember or, if it is close to the next scheduled dose, return to the regular schedule. Do not double dose to catch up.
Wash your hands after giving your pet this medication.
Side Effects
Be sure to discuss any side-effects with your veterinarian immediately.
Reported side-effects in dogs: gastrointestinal upset and reddening or flushing of the skin.
Side effects in humans include headache, nasal congestion, difficulty breathing, prolonged erection and dizziness.
Precautions
Keep this and all drugs out of reach of children. This drug should only be given to the animal for which it was prescribed. Do not give this medication to a person.
Federal law restricts this drug to use by or on the order of a licensed veterinarian. Sildenafil should not be used in animals that are experiencing low blood pressure, shock, blood or fluid loss, or certain heart or lung problems that will not be improved by this drug.
Drug Interactions
Be sure to review with your veterinarian any medications or supplements your pet may be receiving.
Sildenafil should not be used with any drugs that may cause low blood pressure. These include drugs such as: nitrates, nitroprusside sodium, alpha-adrenergic blockers (phentolamine, phenoxybenzamine, phenothiazines), amlodipine, or any other hypotensive drugs.
The following drugs may interact with sildenafil: cimetidine, erythromycin, clarithromycin, ketoconazole, itraconazole, phenobarbital, and rifampin.
Overdose
If you suspect that your pet or another animal has been accidentally overdosed or has eaten this medication inadvertently, contact your veterinarian . Always have the prescription container with you when you take your pet for treatment.

Storage
Different strengths or dosage forms of sildenafil may have different storage requirements. Read the label or ask your pharmacist for the storage requirements of the prescription you receive.