You can take it in a small dose daily or in a larger dose as needed. Both options require valid medical documentation, but some online services only require a health questionnaire to be filled out and reviewed for approval—meaning no face-to-face video interaction is needed. The patient addressed both questions at the final visit for the last 4 weeks of the study. Based upon measurements of sildenafil in semen of healthy volunteers 90 minutes after dosing, less than 0. The pills are available in strengths as high as 20 mg, and hangs around your bloodstream for up to 36 hours. Viagra had no effect on saquinavir pharmacokinetics.Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes . Viagra (sildenafil): As the first FDA-approved PDE5 inhibitor for ED, sildenafil is taken 30 minutes to four hours before sexual intercourse to help achieve . Viagra comes as tablets that you take by mouth, when needed. Available strengths: 25 mg, 50 mg, mg. Viagra comes in these strengths: 25 milligram (mg), .