Impotence and Prostate Cancer Treatment

Men who undergo radical prostatectomy or radiation therapy for prostate cancer often fear they will be unable to resume sexual activity after treatment. Although these procedures may result in ED (erectile dysfunction), they do not directly affect libido or the ability to achieve orgasm. This is in contrast to hormone therapy, which lowers testosterone levels and decreases libido. Several options are available to help men regain lost sexual function.

The penis is made up of nerves, smooth muscle, and blood vessels. Within the penis are two cylindrical chambers—called the corpora cavernosa, or corporal bodies—that extend from the base to the tip. When a man has an erection, smooth muscle tissue within the penis relaxes, causing these spongy chambers to dilate and fill with blood. The swollen corporal bodies press against and close the veins that normally allow blood to flow away from the penis; as a result, the penis remains engorged with blood. After orgasm, the smooth muscle tissue contracts, and blood once again exits the penis.

This process is initiated by signals passing through nerve bundles that run along both sides of the prostate toward the penis. Radical prostatectomy can lead to ED if one or both of these nerve bundles is damaged during surgery. Nerve damage does not affect sensation in the penis, but it does impair a man's ability to achieve a normal erection.

Radiation treatment also can result in ED by damaging these nerve bundles or the arteries that carry blood to the penis. The first treatment used in ED is either a vacuum pump or an oral medication. If these are ineffective or inappropriate, another option is vasodilators (drugs that dilate blood vessels), which are injected or inserted into the penis. Surgical implantation of a prosthesis is an option for men who do not regain sexual function with less invasive forms of treatment.

Vacuum Pumps and ED

A simple, noninvasive treatment for ED is the vacuum pump—an airtight tube that is placed over the penis before intercourse. The tube is attached to a pump, which withdraws air from the tube and creates a partial vacuum that causes the penis to become engorged with blood. A constricting ring is then placed at the base of the penis to prevent blood from flowing back out.

Erections last about half an hour. Leaving the constricting ring on for a longer period may be harmful. Vacuum pumps are highly effective devices, but many men find that they are cumbersome and inconvenient.

Oral Medications and ED

Three oral medications for ED are available: sildenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis). These medications are unlike other ED therapies because they do not produce erections in the absence of sexual stimulation. Normally, sexual arousal increases levels of a substance called cyclic guanosine monophosphate (cGMP) in the penis. Higher levels of cGMP relax smooth muscles in the penis and allow blood to flow into its two inner chambers.

Viagra, Levitra, and Cialis work by blocking the actions of an enzyme called phosphodiesterase type 5 (PDE5), which is found primarily in the penis. PDE5 causes erections to subside by breaking down cGMP. By maintaining increased cGMP levels, the drugs (known as PDE5 inhibitors) enhance both the relaxation of smooth muscles in the corpora cavernosa and the engorgement of these chambers with blood.

As a result, men with ED can respond naturally to sexual arousal. Oral drugs have been tested in a wide range of men with ED. It is not known whether one drug is better than another because the medications have not been compared directly.

Viagra and Levitra are effective for about four hours. Cialis, however, is effective for 24 to 36 hours, making it more convenient and allowing more spontaneity in a man's sexual relationship. Cialis is also now available for daily use in a 2.5-mg or 5-mg dose. Daily Cialis is an appropriate choice for men who anticipate having frequent sexual activity.

Men who take alpha-blockers need to check with their physician before using a PDE5 inhibitor. Levitra cannot be used with alphablockers. Viagra can be used, but not within four hours of taking an alpha-blocker. Cialis can only be used with Flomax—and only at the 0.4-mg per day dosage of Flomax.

PDE5 inhibitors have a number of other potential drug interactions and side effects and must be used with caution in men who have cardiovascular disease.

Vasodilators and ED

Erections can be produced with medications known as vasodilators. These medications expand the blood vessels and allow the penis to become engorged with blood. The most commonly prescribed vasodilator for ED is alprostadil. Other vasodilators include papaverine and phentolamine.

Alprostadil can be injected directly into the base of the penis with a needle or inserted into the urethra in pellet form. Both approaches have drawbacks. Injections can cause discomfort, scarring, and, rarely, priapism—a painful, prolonged erection that must be treated medically. The pellet form, known as the MUSE delivery system, can cause burning in the urethra. Using low doses of alprostadil can minimize the risk of these side effects.

Because vasodilators cause erections by dilating blood vessels—an event that occurs after the nerve signals travel from the nerve bundles to the penis—these medications may work when a PDE5 inhibitor does not. For instance, vasodilators may be effective for men whose nerve bundles are damaged or no longer intact. The injections also may be helpful when used in conjunction with an oral ED medication.

Moreover, researchers recently theorized that regular injections of vasodilators (regardless of whether the injections are followed by sexual activity) might promote the return of normal erections, presumably by re-establishing blood flow to the penis. Based on this theory, many doctors are recommending a more aggressive approach to ED, with treatment beginning shortly after surgery.

Surgery and ED

Several types of surgically implanted devices can provide erections sufficient for sexual intercourse. One, a semi-rigid device (a silicone rod inserted into the penis), is folded upward close to the body until a man is ready for sexual intercourse. Just before intercourse, he bends the device into the erect position.

A more commonly used device consists of two hollow cylinders implanted into the penis, a reservoir placed in the lower abdomen, and a pump placed in the scrotum. To achieve an erection, the man squeezes the pump to move fluid into the cylinders in the penis.

Publication Review By: H. Ballentine Carter, M.D.

Published: 09 Jun 2011

Last Modified: 01 Jul 2011