Erectile dysfunction (ED) is commonly called impotence. It’s a condition in which a man can’t achieve or maintain an erection during sexual performance. Symptoms may also include reduced sexual desire or libido. Your doctor is likely to diagnose you with ED if the condition lasts for more than a few weeks or months. ED affects as many as 30 million men in the United States.
Cavallini, G., Modenini, F., Vitali, G., & Koverech, A. (2005, November). Acetyl-L-carnitine plus propionyl-L-carnitine improve efficacy of sildenafil in treatment of erectile dysfunction after bilateral nerve-sparing radical retropubic prostatectomy. Urology, 66(5), 1080-5. Retrieved from http://www.sciencedirect.com/science/article/pii/S0090429505006515
Name of DrugWhen to TakeDoseDietary RestrictionsViagraTake between 30 and 60 minutes (and up to 4 hours) before sex; works for about 4 hoursRecommended dose for most men is 50mgs; after that, dosage may go to as high as 100mg, or as low as 25mg, which may be prescribed for men over 65.Quickly absorbed by the body, less effective after a high-fat meal, and best taken on an empty stomach.Name of DrugWhen to TakeDoseDietary RestrictionsLevitraTake 1 hour before sex; works for 4 to 5 hours, and may be slightly more effective than ViagraStarting dose for most men is 10mgs a day, but men over 65 often start on the 5mg pill.Can be taken with or without food, although slightly less effective after a high-fat meal. Avoid anything containing grapefruit juice; it may make side effects worse.Name of DrugWhen to TakeDoseDietary RestrictionsCialisComes in two forms. The daily pill stays effective in between doses, but may take 4 to 5 days before it begins working. The “weekender” version of Cialis can start working in as little as 30 minutes for men who take the highest dose of the drug (20mgs); it stays effective in the body for up for 36 hours.Daily pill comes in both a 2.5mg and 5mg tablet; most men start with the lower dose. The use-as-needed, “weekender” pill comes in 5, 10 and 20mg strengths; recommended starting dose is 10mg,Can be taken with or without food. Avoid heavy drinking (5 glasses of wine or 5 shots of whiskey); when combined with Cialis, it can lead to headaches, dizziness, an increase in heart rate, and a drop in blood pressure.Name of DrugWhen to TakeDoseDietary RestrictionsStaxyn Take 1 hour before sex, although many men report erections in 20 to 30 minutes. Because Staxyn comes in a sleek black package and is taken as a rapidly dissolving tablet (without water), some men think of it as a more discrete way to treat ED.Comes in 10mg tablets; do not take more than 1 a day.Avoid taking it with any kind of liquid. Should be placed directly on the tongue and allowed to dissolve without chewing.Name of DrugWhen to TakeDoseDietary RestrictionsStendraPrescribing information now recommends taking it 30 minutes before sex. Some men, however, report results in as little as 10 to 12 minutes, depending on the dose. Because of these findings, Auxilium Pharmaceuticals, the Chesterbrook, Pa., company that has U.S. marketing rights to the drug, has asked the FDA to revise the prescribing information.Starting dose is 100mgs for most men, but the 50mg tablet is recommended for men taking alpha-blocker drugs, like those used for high blood pressure and prostate problems.May be taken with or without food, and with a moderate amount of alcohol (3 drinks). Drinking more than that can increase the chances of side effects like rapid heart rate, low blood pressure, dizziness and headaches.Name of DrugWhen to TakeDoseDietary RestrictionsPenile injections & the MUSE suppositoryTake 5 to 10 minutes before planning to have sex; erections last for 30 to 60 minutes.MUSE comes in 4 dosage strengths; most men start at 125mgs. Avoid taking more than twice within a 24-hour period.N/A
The dorsal artery provides for engorgement of the glans during erection, whereas the bulbourethral artery supplies the bulb and the corpus spongiosum. The cavernous artery effects tumescence of the corpus cavernosum and thus is principally responsible for erection. The cavernous artery gives off many helicine arteries, which supply the trabecular erectile tissue and the sinusoids. These helicine arteries are contracted and tortuous in the flaccid state and become dilated and straight during erection. 
Finally, there are NO-releasing polymers that are capable of delivering NO in a pharmacologically useful way. Such compounds include compounds that release NO upon being metabolised and compounds that release NO spontaneously in aqueous solution. Initial animal studies suggest that cavernosal injections of NO polymers can significantly improve erectile function.48
The causes of erectile dysfunction include aging, high blood pressure, diabetes mellitus, cigarette smoking, atherosclerosis (hardening of the arteries), depression, nerve or spinal cord damage, medication side effects, alcoholism or other substance (drug) abuse, pelvic surgery including radical prostatectomy, pelvic radiation, penile/perineal/pelvic trauma such as pelvic fracture, Peyronie's disease (a disorder that causes curvature of the penis and sometimes painful erections), and low testosterone levels.
Vardenafil and tadalafil belong to the same group of chemical compounds as sildenafil, namely phos-phodiesterase type 5 (PDE-5) inhibitors. Some men cannot benefit from sildenafil or the two newer PDE-5 inhibitors because they have low levels of nitric oxide. British investigators reported in late 2002 that three different types of compounds are being studied as possible medications for men with low levels of nitric oxide. They are Rho-kinase inhibitors, soluble guanylate cyclase activators, and nitric oxide-releasing PDE-5 inhibitors.
Qaseem, A., Snow, V., Denberg, T. D., Casey, D. E., Forciea, M. A., Owens, D. K., & Shekelle, P. (2009). Hormonal testing and pharmacologic treatment of erectile dysfunction: A clinical practice guideline from the American College of Physicians. Annals of internal medicine, 151(9), 639-649. Retrieved from http://annals.org/aim/article/745155/hormonal-testing-pharmacologic-treatment-erectile-dysfunction-clinical-practice-guideline-from