Sildenafil usually should not be taken more than once every 24 hours. Other uses for this medicine This medication is sometimes prescribed for other uses; ask your doctor or pharmacist for more information. Here’s some information to help you get ready and know what to expect from your doctor. Do not start these medications while taking sildenafil without discussing it with your healthcare provider. The amount of medicine that you take depends on the strength of the medicine. These include itraconazole Sporanox, Tolsura , ketoconazole Extina, Ketozole, others and ritonavir Norvir. For erectile dysfunction, some basic questions to ask your doctor include: What’s the most likely cause of my erection problems?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).  · Sildenafil works on the PDE5 enzyme in the lungs to relax the blood vessels. This will increase the supply of blood to the lungs and reduce the workload of the heart. This medicine is available only with your doctor’s prescription. This product is available in the following dosage forms: Tablet. Powder for Suspension. Suspension. Products and services. Erectile dysfunction: Viagra and other oral medications. By Mayo Clinic Staff. Medicines that you take by mouth are called oral medicines. They’re often the first line of treatment for trouble getting or keeping an erection, called erectile dysfunction (ED). Oral medicines for ED usually work well and cause .