Today's mini been is here! Effectiveness of Phenylephrine and Ephedrine as Cardiac Drugs Phenylephrine is an alpha 1-agonist, usually given intravenously in 50-100 mcg boluses but can also be run as an infusion of 20-100 mcg/min. It takes 45-60 seconds to take effect and lasts 5-10 minutes. In this video, Dr. Luis Verduzco discusses the effects of both phenylephrine and ephedrine on the cardiovascular system. The use of phenylephrine causes a few side effects, including potent reflex-bradycardia