Researchers are investigating a newer version of drugs that inhibit the enzyme targeted by Viagra, phosphodiesterase-5 (PDE5).

Cialis. Cialis (IC351) is a potent and highly-selective PDE5 inhibitor and may not affect other parts of the body, including the brain, heart, kidney and eyes. Clinical trials are reporting significant success rates in up to 88% of patients. It appears to take effect in 15 minutes and the effects last up to 24 hours. Improved results were reported in men suffering from erectile dysfunction of varying severity and causes. Common side effects include headache, muscle pain, stomach upset following meals, and back pain.

Vardenafil (Levitra). Levitra is another PDE5 inhibitor currently being investigated. A small study concluded that it increased penile rigidity and tumescence. Further evaluation is warranted.

Angiotensin-Receptor Blockers for Men with Hypertension
Recent drugs known as angiotensin-receptor blockers (ARBs), also known as angiotensin II receptor antagonists are being used to lower blood pressure in men with hypertension. In one study after 12 weeks of treatment with an ARB called losartan (Cozaar), 88% of hypertensive males with sexual dysfunction reported improvement in at least one area of sexuality. The number of men reporting impotence declined from 75.3% to 11.8%. Other ARBs include candesartan (Atacand), telmisartan (Micardis), and valsartan (Diovan).

Testosterone Replacement Therapy
Replacement Therapy for Hypogonadism. Testosterone replacement therapy may be effective in inducing puberty in adolescent boys with hypogonadism and may also be helpful for some adult patients with the condition. Some experts believe testosterone replacement therapy also may be helpful for older men whose testosterone levels are deficient. It may improve bone density, improve energy and mood, increase muscle mass and weight, and heighten sexual interest.

Forms of therapy included the following:

 

• Muscle injections using testosterone enanthate (Andryl, Delatestryl) or cypionate (Andro-Cyp, Depo-Testosterone, Virion) has been the standard administration.  
• Testosterone is now available as a skin patch (Testoderm, Testoderm TTS, Androderm). Depending on the brand, patches may be applied to the skin of the scrotum every 24 hours or to the abdomen, back, thighs, or upper arm. In the latter case, two patches are required every 24 hours. Testoderm and Testoderm TTS may cause less skin irritation than Androderm. The skin patch achieves normal testosterone levels in between 67% and 90% of men.  
• A skin gel (Androgel) is also now available, which in one study achieved normal testosterone levels in 87% of men. A gel applied to the penile skin is being investigated for men with hypogonadism and erectile dysfunction. At this time, however, the gel is applied only to the same parts of the body as the patch.

Oral forms of testosterone are not recommended because of the risk for liver damage when taken for long periods of time. The drug clomiphene has been used successfully for treating hypogonadism related to excessive exercise. If excessive levels of the hormone prolactin cause impotence, the drug bromocriptine (Parlodel) is sometimes helpful.

Testosterone in Men with Normal Levels. Testosterone therapy is not recommended for men with testosterone levels that are normal for their age group. In such men, replacement therapy does not appear to have any benefits for increased bone mass or muscle strength. There is also some concern that replacement therapy in men with normal testosterone levels may increase the risk for the following adverse effects:

 

• Lower HDL (the so-called good cholesterol).  
• Rapid growth of prostate tumors in men with existing prostate cancers. (Although some studies indicate that taking testosterone does not increase the risk for prostate cancer, some experts remain concerned.)  
• Lower sperm count.  
• Possibly cause sleep apnea.  
• Possible increased risk for polycythemia, an abnormal increase in red blood cells.  
• Possible increased risk for benign prostatic hyperplasia.

DHEAS. Dehydroepiandrosterone sulfate (DHEAS) is a male hormone used in the production of testosterone. Levels of this hormone decrease as a man ages. In a 2000 study, men under 60 years old with erectile dysfunction tended to have lower DHEAS levels than their peers. In one small study, those who took DHEAS for 16 weeks experienced some improvement in erectile dysfunction. It is available as a supplement, but should not be taken without the recommendation of a physician. The long-term effects of this potent hormone are unknown, and may be similar to those of testosterone replacement.

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American Urological Association