These medicines are called PDE5 inhibitors. Please expect up to 4 to 6 weeks for reimbursement. Use the oral syringe provided with your medication to measure and take your dose. Do not take a double dose to make up for a missed one. Sildenafil is in a class of medications called phosphodiesterase PDE inhibitors.Generic Viagra (sildenafil) is available as a , , , and milligram (mg) pill and in liquid form. It’s meant to be taken as needed — about an hour before sex — but shouldn’t be. Viagra Coupons, Prices, and Savings Card. Generic Names: Sildenafil Citrate. Brand Names: Revatio. Sildenafil is used to treat male sexual function problems (impotence or erectile dysfunction-ED). Learn more about Viagra oral. 1. This is a generic drug. Even if this drug is covered by Medicare or your insurance, we recommend you compare prices. The recommended dosage of Viagra for erectile dysfunction (ED) is 50 mg, taken as needed about 1 hour before sexual activity. You can take it 30 minutes to 4 hours before sexual activity. And you.