Erectile Dysfunction and Prostate Cancer
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 erectile dysfunction (ED), they do not directly affect libido or the ability to achieve orgasm.
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 or maintain a normal erection. Radiation treatment also can result in ED by damaging these nerve bundles or the arteries that carry blood to the penis. Unlike ED caused by nerve damage, ED from hormone therapy results from lowered testosterone levels, which leads to decreased libido.
Several options are available to help men regain lost sexual function. Typically, the first treatment used is an oral ED medication. If oral medication is ineffective or inappropriate, other options include vasodilators (drugs that dilate blood vessels), which are injected or inserted into the penis, and vacuum pumps. Surgical implantation of a prosthesis is an option for men who do not regain sexual function with less invasive forms of treatment.
Commonly used oral drugs for ED are: sildenafil (Viagra), vardenafil (Levitra), tadalafil (Cialis) and avanafil (Stendra). Unlike other types of ED therapies, these medications 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.
These medications 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, these drugs (known as PDE5 inhibitors or PDE5Is) enhance the relaxation of smooth muscles in the corpora cavernosa and the engorgement of these chambers with blood. As a result, men can respond naturally to sexual arousal.
Viagra and Levitra are effective for about four hours. Cialis is effective for 24 to 36 hours, making it more convenient and allowing more spontaneity in a man’s sexual relationship. Stendra, the newest PDE5I approved by the Food and Drug Administration, is effective for about 5 hours, but has the most rapid onset of action (15 to 30 minutes). It is not known whether one drug is more effective than another because the medications have not been compared directly.
Men who take alpha-blockers need to check with their physician before using a PDE5I. Levitra and Viagra should not be used within four hours of taking an alpha-blocker. PDE5I’s have a number of other potential drug interactions and side effects and must be used with caution in men who have cardiovascular disease.
Erections can be produced with vasodilators, medications that 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 PDE5I 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 theorize 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.
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 approximately 30 minutes. Leaving the constricting ring on for a longer period may be harmful. Vacuum pumps are highly effective devices, but many men find them cumbersome and inconvenient.
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 that are 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.