Some examples of nitrates are nitroglycerin Nitro-Dur, Nitrostat, others , isosorbide mononitrate Monoket and isosorbide dinitrate Bidil. Before taking sildenafil, tell your doctor and pharmacist if you are allergic to sildenafil, any other medications, or any of the ingredients in sildenafil tablet or suspension. You can take sildenafil with or without food. Sildenafil Viagra. These small differences affect the way each medication works, such as how quickly it takes effect and wears off, and the possible side effects. Side effects Side effects of oral ED medicines are often mild. Sildenafil is in a class of medications called phosphodiesterase PDE inhibitors.Sildenafil (Viagra) is a phosphodiesterase-5 (PDE-5) inhibitor. PDE-5 is a protein in your body that breaks down the molecules that normally cause an erection. When it blocks . Viagra generic form Viagra is a brand-name medication. It’s also available in a generic form called sildenafil. How does Viagra work and how long does it last? You may have . Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles .