Impotence, or erectile dysfunction (ED), is the inability to obtain or maintain an erection long enough to engage in sexual intercourse. Normally, upon sexual stimulation, blood flows into the penis. This causes it to expand and harden. In ED, blood vessels leading to the penis don't work properly, leading to decreased blood flow. The standard therapy for ED is a class of drugs called phosphodiesterase inhibitors. Alternate treatments include testosterone replacement and alprostadil.
Phosphodiesterase Inhibitors
Phosphodiesterase inhibitors include sildenafil (Viagra), tadalafil (Cialis) and vardenafil (Levitra). These medications prevent the action of phosphodiesterase Type 5 and allow muscle relaxation and increased blood flow to the penis. The PDE5 inhibitors are given by mouth, providing a convenient route of administration and producing satisfactory erections in about 60 percent to 80 percent of men. Sildenafil and vardenafil exert their action in about one hour and have a short duration of action. Tadalafil has an onset of action of two hours and duration of action of up to 36 hours. Tadalafil possesses the advantage of lasting an entire weekend. According to the book "Pharmacotherapy: A Pathophysiologic Approach," most adverse effects of the PDE5 inhibitors are mild or moderate and rarely require treatment discontinuation. The most common adverse effects are headache, facial flushing, heartburn, nasal congestion and dizziness.
Testosterone Replacement
Testosterone replacement regimens are indicated for people who have primary or secondary hypogonadism, which cause low testosterone levels. Testosterone should never be administered to men with normal testosterone levels. Testosterone can be administered by mouth, by injection, or topically. Although testosterone doesn't directly treat erectile dysfunction, it improves libido and restores muscle strength. An adverse effect of this medication is weight gain due to sodium retention. Worsening of high blood pressure, congestive heat failure (CHF) and water retention are other common side effects. Oral testosterone replacement therapy may cause liver toxicity, which can range from mild to severe; injection testosterone is preferred. Topical patches can cause skin reactions at the site of application.
Alprostadil
Alprostadil stimulates the release of chemicals that relax the muscles in the penis, resulting in increased blood flow. It's available as an intracavernosal injection as the brand names Caverject and Edex, and as an intraurethral insert as the brand name Muse. The intracavernosal injection is more effective than the intraurethral insert due to the site of injection. In the intracavernosal injection, the needle is inserted into the side of the penis, rotating the injection site with each dose. Local site reactions are seen with this medication but decrease over time. The "Pharmacotherapy: A Pathophysiologic Approach" textbook reports that up to 44 percent of men experience discomfort or pain near the site of injection or during an erection. This effect also subsides with continued treatment. Intraurethral alprostadil is administered by inserting the applicator 0.5 inch into the urethra and pushing the pellet into the urethra. The urethra may be injured due to improper administration technique. This can be avoided by receiving complete details on the correct administration procedure. Urethral pain occurs in about 24 percent to 32 percent of men, and female partners may experience vaginal burning or pain from contact with the medication. Discuss any major concerns with your physician.
References
- "Drug Information Handbook 15th Edition"; Charles F. Lacy, RPh, PharmD, FCSHP, Lora L. Armstrong, RPh, PharmD, BCPS. et al; 2007
- "Pharmacotherapy: A Pathophysiologic Approach"; Joseph T. Dipiro, Robert L. Talbert, et al; 2008
- Viagra: About Erectile Dysfuntcion (ED)
