Use with caution in pets with resting hypotension, fluid depletion, severe left ventricular outflow obstruction, bleeding disorders, or autonomic dysfunction. Do not use this medication in pets that are allergic to it or that are currently taking nitrate medications. 

Make sure to tell your veterinarian what other medication you are giving to your pet. Quite often your veterinarian may prescribe two different medications, and a drug interaction may be anticipated. In this case, your veterinarian may vary the dose and/or monitor your pet more closely. Contact your veterinarian if your pet experiences any unusual reactions when different medications are given together. The following drugs can potentially interact with sildenafil: ACE inhibitors, alpha-adrenergic antagonists, alpha-2 adrenergic agonists, amlodipine, angiotensin receptor blockers, azole antifungals, cimetidine, ciprofloxacin, clarithromycin, erythromycin, furosemide, heparin, nitrates, nitroprusside sodium, paclitaxel, phenobarbital, propranolol, or rifampin.  The safe use of sildenafil during pregnancy and in pets that are nursing has not been established. 

Allergic reactions to medications may occur. Be sure to inform Pets Choice and your veterinarian if your pet has any known drug sensitivities or allergies. If your pet displays symptoms of an allergic reaction, call your veterinarian immediately or go to a veterinary emergency clinic. Symptoms may include but are not limited to: swollen lips, tongue, face, airways; difficulty breathing; agitation; profuse salivation; widespread hives and itching.