Erectile dysfunction (ED), formerly known as impotence
, is the inability to achieve or maintain an erection long enough to engage in sexual intercourse.
Under normal circumstances, when a man is sexually stimulated, his brain sends a message down the spinal cord and into the nerves of the penis. The nerve endings in the penis release chemical messengers, called neurotransmitters, that signal the arteries that supply blood to the corpora cavernosa (the two spongy rods of tissue that span the length of the penis) to relax and fill with blood. As they expand, the corpora cavernosa close off other veins that would normally drain blood from the penis. As the penis becomes engorged with blood, it enlarges and stiffens, causing an erection. Problems with blood vessels, nerves, or tissues of the penis can interfere with an erection.
Causes and symptoms
It is estimated that up to 30 million American men frequently suffer from ED and that it strikes up to half of all men between the ages of 40 and 70. Doctors used to think that most cases of ED were psychological in origin, but they now recognize that, at least in older men, physical causes may play a primary role in 60% or more of all cases. In men over the age of 60, the leading cause is atherosclerosis
, or narrowing of the arteries, which can restrict the flow of blood to the penis. Injury or disease of the connective tissue, such as Peyronie's disease, may prevent the corpora cavernosa from completely expanding. Damage to the nerves of the penis from certain types of surgery or neurological conditions, such as Parkinson's disease or multiple sclerosis
, may also cause ED. Men with diabetes are especially at risk for erectile dysfunction because of their high risk of both atherosclerosis and a nerve disease called diabetic neuropathy
Some drugs, including certain types of blood pressure medications, antihistamines
, tranquilizers (especially before intercourse), and antidepressants known as selective serotonin reuptake inhibitors
(SSRIs, including Prozac and Paxil) can interfere with erections. Smoking
, excessive alcohol consumption, and illicit drug use may also contribute. In some cases, low levels of the male hormone testosterone may contribute to erectile failure. Finally, psychological factors, such as stress
, guilt, or anxiety
, may also play a role, even when the ED is primarily due to organic causes.
When diagnosing the underlying cause of erectile dysfunction, the doctor begins by asking the man a number of questions about when the problem began, whether it only happens with specific sex partners, and whether he ever wakes up with an erection. (Men whose dysfunction occurs only with certain partners or who wake up with erections are more likely to have a psychological cause for their ED.) Sometimes, the man's sex partner is also interviewed. In some cases, domestic discord may be a factor.
The doctor also obtains a thorough medical history to find out about past pelvic surgery, diabetes, cardiovascular disease, kidney disease
, and any medications the man may be taking. The physical examination
should include a genital examination, hormone tests, and a glucose test for diabetes. Sometimes a measurement of blood flow through the penis may be taken.
Years ago, the standard treatment for erectile dysfunction was a penile implant or long-term psychotherapy. Although physical causes are now more readily diagnosed and treated, individual or marital counseling is still an effective treatment for ED when emotional factors play a role.
There are three prescription medications available in the United States to treat the physical causes of ED: sildenafil citrate
(Viagra), vardenafil (Levitra), and tadalafil (Cialis). They help about three-fourths of all men who try them in the general population. Several studies have indicated that their success rate in diabetic men may be slightly lower, averaging around 60-65%. All three pills work by enhancing the effects of nitric oxide. This chemical relaxes muscles in the penis to allow more blood to flow in. These pills do not cause an erection by themselves. Sexual stimulation is also required. Sildenafil or vardenafil should be taken about an hour before sex. Each is effective for roughly four hours. Tadalafil lasts for up to 36 hours. Men should not have sex more than once every 24 hours after using these drugs. Before Viagra's approval in 1998, drug treatment of erectile dysfunction was limited to alprostadil (prostaglandin [E.sub.1]), either injected into the penis or inserted as a pellet into the urethra. Sales of the three newer ED drugs reached $3.4 billion in 2004, according to the research firm IMS Health. In 2004, Viagra had about 66% of the market share for ED drugs compared to 19% for Levitra and 14% for Cialis.
Sildenafil citrate was originally developed in 1991 as a treatment for angina
, or chest pain
. The drug, marketed under the name Viagra, received FDA approval as a treatment for erectile dysfunction in March 1998, and since that time it has been prescribed for more then 20 million men worldwide. It was the first oral medication approved for ED treatment. Viagra is a vasodilator, a drug that has the effect of dilating the blood vessels. It works by improving blood circulation to the penis, and by enhancing the effects of nitric oxide, the agent that relaxes the smooth muscle of the penis and regulates blood vessels during sexual stimulation, allowing the penis to become engorged and achieve an erection.
The average recommended dose of Viagra is 50 mg. It comes in doses of 25 mg., 50 mg., and 100 mg to. The medication is taken approximately one hour before sexual activity is planned, and may remain effective for up to four hours. One drawback is that to be effective, it should be taken on an empty stomach. Also, high-fat foods can interfere with the absorption of Viagra. Viagra does not increase sexual desire. Sexual stimulation and arousal are required for it to be effective.
Many insurance plans cover the cost of Viagra, provided it is prescribed to treat erectile dysfunction. The pills cost approximately $10 each, and insurers may limit coverage to a specific number of pills each month.
The primary drawback to Viagra, which works about an hour after it is taken, it that the FDA cautions men with heart disease or low blood pressure to be thoroughly examined by a physician before obtaining a prescription. At least 130 men have died while taking Viagra. However, the FDA said the men—most over the age of 64—died of heart attack
due to health problems exaggerated by sexual activity, not the drug itself.
In early 2003, a second prescription drug to treat erectile dysfunction, Levitra, was approved by the FDA. Like Viagra, Levitra helps increase blood flow to the penis and may help men with ED get and keep an erection. Once a man has completed sexual activity, blood flow to the penis should decrease and the erection should go away. Levitra should be taken approximately 60 minutes prior to sexual activity. In clinical trials, most patients were able to begin sexual activity before that time. A 2004 study showed that about 50% of men taking Levitra experienced a firm erection within 25 minutes and a small percentage in as quickly as 10 minutes. Studies also showed that Levitra improved erectile function in men who had other health factors, such as diabetes or prostate surgery.
Men taking nitrate drugs, often used to control chest pain (also known as angina), should not take Levitra. Men who use alpha-blockers, sometimes prescribed for high blood pressure or prostate problems, also should not take Levitra. Such combinations could cause blood pressure to drop to an unsafe level. Levitra is available in 2.5 mg, 5 mg, 10 mg, and 20 mg tablets and should be taken no more than once a day. The average cost per pill is about $10 and is covered by many insurance plans.
Cialis is the third oral drug prescribed to treat erectile dysfunction, approved by the FDA in November 2003. Its most notable difference from Viagra and Levitra, which work for about four hours, is that Cialis works for up to 36 hours. Cialis helps increase blood flow in the penis when a man is sexually stimulated. It can help men with ED get and keep an erection satisfactory for sexual activity. Once a man has completed sexual activity, blood flow to his penis decreases, and his erection goes away. Cialis is clinically proven to improve erectile function in most men with ED, including those with mild, moderate or severe ED.
The most common side effects with Cialis are headache
, upset stomach, back pain, and muscle aches. These side effects usually go away after a few hours. Patients who get back pain and muscle aches usually get it 12 to 24 hours after taking Cialis. Back pain and muscle aches usually go away by themselves within 48 hours.
Cialis comes in 5 mg., 10 mg. (the recommended starting dose), and 20 mg. tablets. The average cost per tablet is about $10 and it is covered by many insurance plans. Since the absorption of Cialis is not affected by food or high-fat foods, it does not need to be taken on an empty stomach. Studies show that in most men, Cialis begins working in about 30 minutes and may be taken up to once per day by most patients.
, a prolonged erection, is a very rare potential side effect of all prescription ED medications. Persons taking Viagra, Levitra, or Cialis who have a prolonged erection, lasting more than four hours, should seek immediate medical attention. Priapism can cause damage to the penis potentially leading to the permanent inability to have an erection.
Because sexual activity can stress the heart, men who have heart problems should check with their physician to see if sexual activity is recommended. Erectile dysfunction drugs may trigger temporary hypotension
(low blood pressure) and is known to increase cardiovascular nerve activity, so physicians should prescribe them with caution in men with a history of heart attack, atherosclerosis (hardening of the arteries), angina, arrhythmia, and chronic low blood pressure problems. ED drugs are not labeled or approved for use by women or children, or by men without erectile dysfunction. Anyone experiencing cardiovascular symptoms such as dizziness
, chest or arm pain, and nausea when participating in sexual activity after taking an ED medication should stop the encounter. They should also not take any ED drug again until they have discussed the episode with their healthcare provider. It is recommended that men with kidney or liver impairments, and men over age 65, start at the lowest possible dosage of ED medications.
Other treatment options
Although the commercial availability of Viagra, Levitra, and Cialis has been useful in many men, prostate cancer
patients and ED caused by psychological problems often require alternative treatment. A commonly used alternative consists of a three-drug injection containing alprostadil, papaverine hydrochloride, and phentolamine mesylate. Though it is commonly referred to as the "Knoxville formula," apparently for the city of its original introduction, a number of slightly varying formulas have been in use around the country. The three-drug preparation is administered by injection into the corpora cavernosa to induce erection.
Other traditional therapies for ED include vacuum pump therapy, injection therapy involving injecting a substance into the penis to enhance blood flow, and a penile implantation device. In rare cases, if narrowed or diseased veins are responsible for ED, surgeons may reroute the blood flow into the corpora cavernosa or remove leaking vessels.
In vacuum pump therapy, a man inserts his penis into a clear plastic cylinder and uses a pump to force air out of the cylinder. This forms a partial vacuum around the penis, which helps to draw blood into the corpora cavernosa. The man then places a special ring over the base of the penis to trap the blood inside it. The only side effect with this type of treatment is occasional bruising if the vacuum is left on too long.
Injection therapy involves injecting a substance into the penis to enhance blood flow and cause an erection. The FDA approved a drug called alprostadil (Caverject) for this purpose in 1995. Alprostadil relaxes smooth muscle tissue to enhance blood flow into the penis. It must be injected shortly before intercourse. Another, similar drug that is sometimes used is papaverine. Either drug may sometimes cause painful erections or priapism that must be treated with a shot of epinephrine. Alprostadil may also be administered into the urethral opening of the penis. In MUSE (medical urethral system for erection), the man inserts a thin tube the width of a spaghetti noodle into his urethral opening and presses down on a plunger to deliver a tiny pellet containing alprostadil into his penis. The drug takes about 10 minutes to work and the erection lasts about an hour. The main side effect is a sensation of pain and burning in the urethra, which can last about five to 15 minutes. The injection process itself is often painful
Implantable penile prostheses
are usually considered a last resort for treating erectile dysfunction. They are implanted in the corpora cavernosa to make the penis rigid without the need for blood flow. The semi-rigid type of prosthesis consists of a pair of flexible silicone rods that can be bent up or down. This type of device has a low failure rate but, unfortunately, it causes the penis to always be erect, which can be difficult to conceal under clothing.
The inflatable type of device consists of cylinders that are implanted in the corpora cavernosa, a fluid reservoir implanted in the abdomen, and a pump placed in the scrotum. The man squeezes the pump to move fluid into the cylinders and cause them to become rigid. (He reverses the process by squeezing the pump again.) While these devices allow for intermittent erections, they have a slightly higher malfunction rate than the silicon rods. Men can return to sexual activity six to eight weeks after implantation surgery. Since implants affect the corpora cavernosa, they permanently take away a man's ability to have a natural erection.
A number of herbs have been promoted for treating erectile dysfunction. The most widely touted is yohimbe (Corynanthe yohimbe), derived from the bark of the yohimbe tree native to West Africa. It has been used in Europe for about 75 years to treat ED. The FDA approved yohimbe as a treatment for ED in the late 1980s. It is sold as an over-the-counter dietary supplement and as a prescription drug under brand names such as Yocon, Aphrodyne, Erex, Yohimex, Testomar, Yohimbe, and Yovital.
There is no clear medical research that indicates exactly how or why yohimbe works in treating ED. It is generally believed that yohimbe dilates blood vessels and stimulates blood flow to the penis, causing an erection. It also prevents blood from flowing out of the penis during an erection. It may also act on the central nervous system, specifically the lower spinal cord area where sexual signals are transmitted. Studies show it is effective to some degree in 30-40% of men with ED. It is primarily effective in men with ED caused by vascular, psychogenic (originating in the mind), or diabetic problems. It usually does not work in men whose dysfunction is caused by organic nerve damage. In healthy men without ED, yohimbe in some cases appears to increase sexual stamina and prolong erections. The usual dosage of yohimbine (yohimbe extract) to treat ED is 5.4 mg three times a day. It may take three to six weeks for it to take effect.
Ginkgo Ginkgo biloba
, is also used to treat erectile dysfunction, although it has not been shown to help the condition in controlled studies, and probably has more of a psychological effect. In addition, ginkgo carries some risk of abnormal blood clotting and should be avoided by men taking blood thinners, such as coumadin. Other herbs promoted for treating ED include true unicorn root Aletrius farinosa
, saw palmetto Serenoa repens
, ginseng Panax ginseng
, and Siberian ginseng Eleuthrococcus senticosus
. Nux vomica Strychnos nux-vomica
has been recommended, especially when ED is caused by excessive alcohol, cigarettes, or dietary indiscretions. Nux vomica can be very toxic if taken improperly, so it should be used only under the strict supervision of a physician trained in its use.
There are quite a few Chinese herbal remedies for erectile dysfunction usually combinations of herbs and sometimes animal parts such as deer antler and sea horse. Acupuncture
is also used to treat ED, although Western doctors question its effectiveness.
— A condition in which lack of blood to the heart causes severe chest pain.
— A drug that blocks cell receptors for histamine, usually to prevent allergic effects such as sneezing and itching.
— An irregularity in the normal rhythm or force of the heartbeat.
— An arterial disease in which raised areas of degeneration and cholesterol deposits (plaques) form on the inner surfaces of the arteries. Also called hardening of the arteries.
— Either of a pair of columns of erectile tissue at either side of the penis that, together with the corpus spongiosum, produce an erection when filled with blood.
— A disease or disorder, especially a degenerative one, caused by diabetes that affects the nervous system.
— A chemical that carries messages between different nerve cells or between nerve cells and muscles.
— Local fibrous scarring causing the erect penis to be bent to such a degree that it interferes with sexual intercourse.
— A prolonged erection lasting more than four hours.
— Selective serotonin reuptake inhibitors, a class of medication used to treat depression.
— An agent, such as a nerve or hormone, that widens the blood vessels, which in turn decreases resistance to blood flow and lowers blood pressure.
With proper diagnosis, erectile dysfunction can nearly always be treated or coped with successfully. Unfortunately, fewer than 10% of men with ED seek treatment. However, with the heavy advertising and marketing associated with Viagra, Levitra, and Cialis, this number is expected to rise dramatically.
There is no specific treatment to prevent erectile dysfunction. Perhaps the most important measure is to maintain general good health and avoid atherosclerosis by exercising regularly, controlling weight, controlling hypertension
and high cholesterol levels, and not smoking. Avoiding excessive alcohol intake may also help.
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Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.