Do not take a double dose to make up for a missed one. What should I do if I forget a dose? Severe liver disease. 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. Ask your pharmacist or doctor for a copy of the manufacturer’s information for the patient. Do not mix the liquid with other medications or add anything to flavor the medication. Check with your doctor right away if you have a sudden decrease in hearing or loss of hearing, which may be accompanied by dizziness and ringing in the ears.Take sildenafil (Revatio) 3 times day and separate the doses by 4 to 6 hours. Taking it more frequently can raise your risk of side effects. There is usually no benefit to taking more than 20 mg 3 times a day, though some medical specialists will recommend higher strengths (still taken 3 times a day). 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 adults (Liqrev, Revatio) and children 1 year of age and older (Revatio) with pulmonary arterial hypertension (PAH; high blood pressure in the vessels carrying blood to the . swelling in your hands, ankles, or feet; shortness of breath; seizure (convulsions); or. a light-headed feeling, like you might pass out. Common Viagra side effects may include: flushing (warmth, redness, or tingly feeling); headache, dizziness; abnormal vision (blurred vision, changes in color vision) runny or stuffy nose, nosebleeds;.