Tell your doctor if any of these symptoms are severe or do not go away: headache. Viagra vs. Describe the clinically important drug interactions of sildenafil. Levitra vardenafil : This medication is taken one hour before sex and can last up to 24 hours. While each PDE5 inhibitor differs slightly, they’re very similar in treating erectile dysfunction. Finding an online ED provider can feel overwhelming.For oral dosage forms (suspension or tablets): Adults—20 milligrams (mg) 3 times a day. Your doctor may adjust your dose as needed and tolerated. However, the dose is usually not more than 80 mg 3 times a day. Children 1 year of age and older weighing 45 kilograms (kg) or more—20 mg 3 times a day. Sildenafil (Viagra, Revatio) is a moderately priced drug used to treat erection problems in men. It is also used to treat pulmonary arterial hypertension, a serious heart and lung condition. This drug is more popular than comparable drugs. It is available in generic and brand versions. If you have these symptoms, stop taking VIAGRA and contact a doctor right away. have or have had heart problems such as a heart attack, irregular heartbeat, angina, chest pain, narrowing of the aortic valve, or heart failure. have low blood pressure, or high blood pressure that is not controlled.