After reading this article, the reader should be able to: (1) Discuss the worldwide prevalence of erectile dysfunction and the risk factors that cause it. (2) Describe the physiology of an erection and the role phosphodiesterase enzyme 5 (PDE5) and PDE5 inhibitors play in it. (3) Understand the effectiveness (including efficacy in multiple patient populations, onset of action, duration of effect, and drug?drug/drug?food interactions) and safety of each of the PDE5 inhibitors.
In the past, erectile dysfunction (ED) was taboo for public discussion, but it has now gained social and medical recognition as a condition affecting millions of men. More than a decade ago, a National Institutes of Health Consensus Conference defined ED as "the consistent inability to achieve and maintain a penile erection adequate for satisfactory sexual intercourse."1 The word consistent is used because an occasional episode of ED occurring in men is normal.
An estimated 150 million men worldwide have some degree of ED, and more than twice that many are expected to be affected by 2025.2 Given that age-related hormonal changes contribute to the overall prevalence, the impact of ED has particular implications for the United States, where the population is expected to grow increasingly older in the coming years.
Scope of the Problem
The historical view of ED as a private matter has complicated efforts to determine the prevalence of the condition. Some of the first systematically collected data came from the Massachusetts Male Aging Study (MMAS), a survey of 1700 men aged 40 to 70 years.3 Responses to the survey showed that 52% of the men reported some degree of ED. The MMAS data also documented an age-related increase in prevalence, as 40% of men aged 40 to 49 complained of mild, moderate, or severe ED, increasing to almost 70% of men aged 70 to 79. A majority of men 60 years or older reported moderate or severe ED.
An update of MMAS showed that the incidence of ED increased about 2-fold with each decade of life.4 Extrapolation of that data to the US population would result in an estimated 617 715 new cases of ED each year among white men 40 to 70 years old.5
Another US study of 2115 men, aged 40 to 79 years, revealed an overall prevalence of severe ED (defined as having erections infrequently or not at all in response to stimulation) of 11.6%. Prevalence increased from 1% among the youngest men to 25% in the oldest age group.6
Studies involving men from other countries have demonstrated that high rates of reported ED are not limited to the United States. The Cologne Male Survey showed a 19.2% prevalence of ED among 4489 German men aged 30 to 80 years. The study also documented a sharp age-related increase in prevalence.7 An Australian study involving general medical practitioners showed a 34% prevalence of ED among male patients, including complete inability to achieve an erection in 12% of the men.8 Other studies have demonstrated rates of ED ranging between 5% and 55%.9
Risk Factors for ED
ED was once considered primarily a psychogenic disorder, but that view has given way to evidence showing that a variety of factors can adversely affect the ability to achieve an erection, including numerous medical conditions.5,9 Some studies have indicated that the vast majority of cases have an organic etiology (Table).10-12
Vascular disorders, particularly atherosclerosis, are thought to be the most common organic causes of ED.12 Some evidence suggests ED is a marker for underlying cardiovascular disease. For example, a study of almost 1000 men seeking consultation for ED showed that 18% had undiagnosed hypertension, 16% had diabetes, and 5% had ischemic heart disease.13
In general, conditions that cause peripheral vascular disease adversely affect penile arteries and can lead to ED. Examples include hypertension, diabetes, dyslipidemia, and smoking.5 The association has led some authorities to conclude that treatment of risk factors for vascular disease offers a promising but never proven approach to prevention of ED.14 Diabetes has a particularly strong association with ED. In MMAS, 28% of men with diabetes reported complete impotence, compared with 10% of the population without diabetes.3 Studies in other countries have found that as many as 60% of men with diabetes report varying degrees of ED.9
Other potential causes of ED include neurologic disorders and injuries, hormonal abnormalities, alcohol abuse, obesity, and certain prescription medications.
Psychogenic factors still contribute to some cases of ED and should not be discounted in the evaluation of a patient. These factors often manifest as circumstantial or situational dysfunction or performance anxiety.5
ED affects millions of men worldwide and increases in prevalence with age. Men report varying degrees of difficulty in achieving and maintaining erections throughout the world. Once considered primarily a psychogenic disorder, ED now has a well-established association with a variety of organic causes, vascular disease being among the most prominent. By recognizing the prevalent nature of ED and it association with organic causes, clinicians will be better prepared to diagnose and treat the condition.
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