During sexual arousal, nerve impulses increase blood flow to both of these cylinders. Take sildenafil as needed before sexual activity. If you become pregnant while taking sildenafil, call your doctor. Taking medications does not automatically produce an erection. Problems getting or keeping an erection can also be a sign of an underlying health condition that needs treatment and a risk factor for heart disease. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule.Drug Images What is Viagra? Viagra is a brand-name prescription drug that’s approved to treat erectile dysfunction (ED). With ED, you’re unable to have or maintain an erection. . What other drugs will affect Viagra? drugs to treat high blood pressure or a prostate disorder; an antibiotic – clarithromycin, erythromycin, or telithromycin; antifungal . Sildenafil pronounced as (sil den’ a fil) Why is this medication prescribed? How should this medicine be used? Other uses for this medicine What special precautions should I .