If it is not treated right away, priapism can permanently damage your penis sudden vision loss in one or both eyes. You can take this medicine with or without food 30 minutes before sex, depending on the dose. 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. Children 1 year of age and older weighing 20 to 45 kg—20 mg 3 times a day. Do not use more of it and do not use it more often than your doctor ordered.The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. How much does sildenafil citrate or revatio cost near you? Find the best sildenafil citrate or revatio prices near you now with our cost comparison tool and start saving today. 2 days ago · How much does Viagra cost online? What dosage is available? Hims: yes: yes – starting at $ per dose of Viagra – starting at $4 per dose of sildenafil, depending on dosage: 25– mg.