They include dutasteride Avodart, Jalyn and finasteride Propecia, Proscar. Follow the manufacturer’s directions to use and clean the oral syringe. The best time to take sildenafil is about 1 hour before sexual activity, but you can take the medication any time from 4 hours to 30 minutes before sexual activity. This boosts blood flow and helps you get an erection from sexual activity. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide.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 (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or .