Brand names Why is this medication prescribed? Sildenafil usually should not be taken more than once every 24 hours. Tell your doctor or pharmacist if you are taking nitrates medications for chest pain such as isosorbide dinitrate Isordil , isosorbide mononitrate Monoket , and nitroglycerin Nitromist, Nitro-Dur, Nitrostat. Sildenafil Liqrev, Revatio is used to improve the ability to exercise in adults Liqrev, Revatio and children 1 year of age and older Revatio with pulmonary arterial hypertension PAH; high blood pressure in the vessels carrying blood to the lungs, causing shortness of breath, dizziness, and tiredness. Researching the cost ahead of time will give you a ballpark pricing figure for the amount you should expect to spend on your medication and will make it easier to spot a counterfeiter, who will typically sell their product for a fraction of the cost of the real thing.Be sure to tell your doctor and pharmacist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products). Tell your doctor if your condition does not. Drug Facts Common Brands Viagra Drug Class PDE-5 inhibitor Controlled Substance Classification Not a controlled medication Generic Status Lower-cost generic available Availability Prescription only How Sildenafil (Viagra) works Sildenafil (Viagra) is a phosphodiesterase-5 (PDE-5) inhibitor. You should not need a new prescription for this medication to be refilled. Your doctor will write the number of refills authorized on your prescription. Travel.