Sildenafil may not be safe to take for people with certain medical conditions including: a past history of stroke or heart attack in the last 6 months retinitis pigmentosa an eye disease It can also interact with many other medicines, particularly nitrates used in heart disease , amyl nitrite and blood pressure medicines. Key facts It usually takes 30 to 60 minutes for sildenafil to work for erectile dysfunction. Kidney disease that needs to be treated with dialysis. Viagra is always taken as needed, usually about an hour before sex. If you are taking sildenafil for erectile dysfunction, your doctor will probably start you on an average dose of sildenafil and increase or decrease your dose depending on your response to the medication. Do not mix the liquid with other medications or add anything to flavor the medication.The Savings Offer and Program expire on 12/31/ For further information, call , visit test1.ru, or write: Viatris Inc., P.O. Box , Mission, KS Eligible patients may save on their VIAGRA® (sildenafil citrate) prescription with the VIAGRA savings card. Sildenafil Prices, Coupons and Patient Assistance Programs. Sildenafil is a member of the agents for pulmonary hypertension drug class and is commonly used for Erectile .  · Maximum dose: 20 mg orally three times a day. Injection: Initial dose: or 10 mg IV bolus three times a day. Comments: No greater efficacy was achieved with oral doses higher than the maximum recommended dose. A 10 mg injection dose is predicted to provide pharmacological effect equivalent to the 20 mg oral dose.