You take one 2. Contact your medical provider if you experience any side effects during treatment. BPH occurs when the prostate and the surrounding tissues become enlarged. This increase in blood flow results in a firmer, longer-lasting erection. The results showed the combination to be even more effective than either medication alone. If you have an erection that lasts more than 4 hours, get medical help right away.Intravenous Solution 10 mg/ mL sildenafil intravenous solution from $ for milliliters Oral Powder For Reconstitution 10 mg/mL sildenafil oral powder for reconstitution from $7, for milliliters Oral Tablet 20 mg sildenafil oral tablet from $ for 10 tablets 25 mg sildenafil oral tablet from $ for 30 tablets. By Ginger Skinner Last updated: June 14, If you’re looking for a less costly Viagra, you might want to ask your doctor about sildenafil. It’s the active ingredient in both branded Viagra. How Cialis Works. Tadalafil and other PDE5 inhibitors primarily work by inducing muscle relaxation. Tadalafil stops the breakdown of a chemical responsible for relaxing muscles. In ED and PAH, the drug targets muscle cells in blood vessels. When the blood vessel muscle cells relax, this expands the vessel and increases blood flow; this .