Some examples of nitrates are nitroglycerin Nitro-Dur, Nitrostat, others , isosorbide mononitrate Monoket and isosorbide dinitrate Bidil. Vardenafil usually works for 4 to 5 hours. You can take sildenafil with or without food. Do not stop taking sildenafil without talking to your doctor. Take sildenafil as needed before sexual activity. These include a heart attack, stroke or a serious heart rhythm disorder in the past six months.Viagra dosage is not based on weight, but your age can affect your dosage. Specifically, you may have a lower starting dosage than usual if you’re over age For example, a . The original little blue pill prescribed by doctors for over 20 years Clinically proven to treat men with erectile dysfunction (ED) Ongoing commitment to product quality and safety . Sildenafil (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or alcohol. Its effects .