Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men. Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in .These medicines are called PDE5 inhibitors. Take sildenafil at around the same times every day. These include a heart attack, stroke or a serious heart rhythm disorder in the past six months. It lasts 4 to 5 hours, or longer if you have mild to moderate ED. Ask your pharmacist or doctor for a copy of the manufacturer’s information for the patient.Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes . Typical dosing for Sildenafil (Viagra) The typical dose is to take 50 mg of sildenafil (Viagra) by mouth, about 1 hour before sex, as needed. The maximum . Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a prescription drug that’s used in adult .You can take this medicine with or without food 30 minutes before sex, depending on the dose. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine. Medicines that you take by mouth are called oral medicines. This can happen if you are sick with fever, diarrhea, or vomiting; sweat a lot; or do not drink enough liquids. Severe liver disease. Some medications should not be taken with sildenafil. These include itraconazole Sporanox, Tolsura , ketoconazole Extina, Ketozole, others and ritonavir Norvir.