Do not take a double dose to make up for a missed one. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Preparing for your appointment You’re likely to start by seeing your family doctor. Sudden vision loss in one or both eyes can be a sign of a serious eye problem called non-arteritic anterior ischemic optic neuropathy NAION. Avanafil Stendra. Tell your doctor or pharmacist if you are taking nitrates medications for chest pain such as isosorbide dinitrate Isordil , isosorbide mononitrate Monoket , and nitroglycerin Nitromist, Nitro-Dur, Nitrostat.Viagra (sildenafil) is a prescription drug that’s used to treat erectile dysfunction (ED). The drug comes as a tablet you’ll take by swallowing. It’s usually taken as needed about 1 . The safest way to get a prescription for Viagra is from your doctor. You can even do this over a telehealth call (on the phone or computer) in many cases, although for your first . If you are taking sildenafil (Viagra) for erectile dysfunction, do not take any more doses of sildenafil (Viagra) or similar medications such as tadalafil (Cialis) or vardenafil (Levitra) .