Medicines that block an enzyme called CYP3A4. Box , Mission, KS If your pharmacy does not participate, you may be able to submit a request for a rebate in connection with this Savings Offer. This medicine also works best when you take it an hour before sex on an empty stomach. Avanafil Stendra. Medicines that you take by mouth are called oral medicines. Some examples of nitrates are nitroglycerin Nitro-Dur, Nitrostat, others , isosorbide mononitrate Monoket and isosorbide dinitrate Bidil. You can take this medicine with or without food 30 minutes before sex, depending on the dose.Oral medicines for ED usually work well and cause few side effects. The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. Thankfully, a generic version of the popular medication — sildenafil — is now widely available from a number of different drug manufacturers at a fraction of the cost. But . Consumer Reports Best Buy Drugs shares how you might be able to get generic Viagra, known as sildenafil, at a much lower price.