Often, these are prescribed for chest pain called angina. In this case, just leave out the missed dose and take your next dose at the usual time. Take sildenafil as needed before sexual activity. Its effects might last longer if you have mild to moderate ED. Some examples of nitrates are nitroglycerin Nitro-Dur, Nitrostat, others , isosorbide mononitrate Monoket and isosorbide dinitrate Bidil.Prices for Sildenafil (Revatio) are as low as $ with a GoodRx coupon. There is usually no benefit to taking more than 20 mg 3 times a day, though some medical specialists will recommend higher strengths (still taken 3 times a day). White Round R And 20 – Sildenafil Citrate 20mg Tablet. This medicine is White, Round Tablet . Generic sildenafil is covered by most Medicare and insurance plans, but some pharmacy coupons or cash prices may be lower. Get sildenafil for as low as $, which is 95% .  · Maximum dose: 20 mg orally three times a day. Injection: Initial dose: or 10 mg IV bolus three times a day. Comments: No greater efficacy was achieved with oral doses higher than the maximum recommended dose. A 10 mg injection dose is predicted to provide pharmacological effect equivalent to the 20 mg oral dose.