An inherited eye disease that affects the retina. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Please expect up to 4 to 6 weeks for reimbursement. If you have an erection that lasts more than 4 hours, get medical help right away. Storage Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light.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. Do not take VIAGRA if you take medicines called guanylate cyclase stimulators which include: –Riociguat (Adempas ®) a medicine that treats pulmonary arterial hypertension and chronic-thromboembolic pulmonary hypertension. Tell all .  · Adults 65 years of age and older—25 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. Children—Use is not recommended.