Challenges in oral therapy for erectile dysfunction.

Erectile dysfunction (ED) is the persistent inability to attain or maintain a penile erection sufficient to permit satisfactory sexual intercourse (NIH Consensus Conference, 1993). It is a highly prevalent medical condition that affects 52% of men between 40 and 70 years of age to some degree (Feldman et al, 1994). Although ED is not an inevitable consequence of aging, its prevalence and severity increase with age (Feldman et al, 1994; Laumann et al, 1999). For example, the Massachusetts Male Aging Study found that the probability of complete impotence tripled between the ages of 40 and 70 years (Feldman et al, 1994). In the United States alone, it is estimated that ED afflicts 30 million men, but only 10% have received treatment (NIH Consensus Conference, 1993; American Association of Retired Persons, 1999). As the world’s population continues to increase and to live longer, it is predicted that 322 million men worldwide will suffer from this disorder by the year 2025 (Aytac et al, 1999).