Males between the ages of 30 and 65 would be eligible to buy four tablets after a consultation with a pharmacist. Oral medicines for ED usually work well and cause few side effects. Ask your pharmacist for a list of the ingredients. Sildenafil works on the PDE5 enzyme in the lungs to relax the blood vessels. If you are taking sildenafil for erectile dysfunction, you are unlikely to miss a dose since this medication is taken as needed, not on a regular dosing schedule.What is sildenafil? Sildenafil is a prescription drug. It comes in the form of a tablet and suspension (liquid). Both are taken by mouth. It also comes in an . Sildenafil is in a class of medications called phosphodiesterase (PDE) inhibitors. Sildenafil treats erectile dysfunction by increasing blood flow to the penis during sexual .  · Sildenafil under the name Viagra is used to treat erectile dysfunction (impotence) in men. Another brand of sildenafil is Revatio, which is used to treat Missing: meaning.