Cochrane Database Syst Rev. These medicines are called PDE5 inhibitors. Children—Use is not recommended. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine. Geographic and clinical variation in clozapine use in the United States.Why is this medication prescribed? Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men.  · Sildenafil (Oral Route) Description and Brand Names. Drug information provided by: Merative, Micromedex ®. US Brand Name. Revatio. Viagra. Descriptions. . Oral medicines for ED usually work well and cause few side effects. The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil .