If you see air bubbles in the syringe, repeat the steps. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. Patients should always ask their doctors for medical advice about adverse events. If you have an erection that lasts for more than 4 hours, you should go to the nearest hospital emergency department. This medicine can cause serious side effects in patients with heart problems. Stop taking VIAGRA and call your healthcare provider right away if you have any sudden vision loss sudden hearing decrease or hearing loss.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 recommended dose is mg. Don’t take sildenafil (Viagra) more than once daily (at any dose). Written by Brian Leonard, PharmD, BCACP, BCGP.  · For treatment of erectile dysfunction: For oral dosage form (tablets): Adults up to 65 years of age—50 milligrams (mg) as a single dose no more than once a day, 1 hour before sexual intercourse. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. Your doctor may adjust your dose if needed.  · Generic name: sildenafil (oral) [ sil-DEN-a-fil ] Brand names: Revatio, Viagra Drug classes: Agents for pulmonary hypertension, Impotence agents. Medically reviewed by Kaci Durbin, MD. Last updated on Uses; Warnings; Before taking; Dosage; Side effects; Interactions; FAQ; What is sildenafil?