Penile erection dysfunction

Erectile dysfunction (ED) is the failure to achieve a penile erection suitable for sexual intercourse. Patients often refer to it as impotence. 

At clinical trials, sildenafil did not work well as a treatment for angina. Instead, it was observed that it overcomes erectile dysfunction. Later, it was found that cyclic GMP also increases the level of nitric oxide, which is needed in penile erections. 

Phase I trials in the United States (Figure 10.16). Although UK-92,480 appeared to be safe, it had little impact on blood pressure, heart rate, and cardiac output. In a 1992 study, some volunteers receiving multiple doses reported an increased incidence of penile erections. Preliminary data was not overwhelming, but Pfizer spent another two years investigating the potential market for an erectile dysfunction drug. A study involving 300 patients in 1994 and 1995 showed excellent results for UK-92,480, which had been... 

Erectile dysfunction, that is, the inability to maintain penile erection for the successful performance of sexual activity, has both organic and psychogenic causes, including as a sequelae to prostatic surgery. Erectile dysfunction is estimated to affect up to 30 million men in the United States. Previous therapies have included penile implants, and intrape-nile injections of alprostadil (see p. 420). Sildenafil [sil DEN a HI], the first oral drug approved for the treatment of erectile dysfunction in males, was introduced in early 1998. 

Treatment should be discontinued if prolonged penile erection occurs because of the risk of permanent erectile dysfunction... 

In addition to the effects on the reproductive functions of the female, there has been some study of the effects of tropic acid esters and related compounds on sexual function In che male. One paper on this topic (125) has been mentioned above. Horowitz and Goble (143) have reviewed the literature on drug-induced sexual dysfunction In the male and have concluded chat any drug with acroplne-llke effects may Interfere with penile erection. (They pointed out that Impotence induced by anclmuscarl e drugs may occur without reduction of libido and may thus be particularly frustrating to the male.)... 

Erectile dysfunction (ED), the inability to achieve or maintain a penile erection sufficient to permit satisfactory sexual intercourse, is estimated to affect over 100 million men worldwide, with a prevalence of 39% in those of 40 years. Its numerous causes include cardiovascular disease, diabetes mellitus and other endocrine disorders, alcohol and substance abuse, and psychological factors (14%). While the evidence is not conclusive, drug therapy is thought to underlie 25% of cases, notably from antidepressants (SSRI and tricyclic), phenothiazines, cypro-terone acetate, fibrates, levodopa, histamine H -receptor blockers, phenytoin, carbamazepine, allopurinol, indomethacin, and possibly adrenoceptor blockers and thiazide diuretics. 

A 49-year-old man with Parkinson s disease was treated with ropinirole, and the dosage eventually reaching 3 mg tds. He had penile erections 20-30 minutes after each dose, lasting for 10-15 minutes. They were not associated with arousal and were very uncomfortable he had no history of sexual dysfunction. Their frequency diminished with a reduction in drug dosage, but they stopped completely only on drug withdrawal. 

Stallions may have problems with penile erection secondary to traumatic injury of the penis. In other stallions, ejaculatory dysfunction, secondary to neurological and musculoskeletal problems that affect the stallion s ability to mount and thrust, may be the primary cause of breeding failure. In these cases, ejaculation in copula or ex copula may be enhanced pharmacologically. 

Melanotan II or PT-141 (Palatin Technologies) is a synthetic analog of melanocyte-stimulating hormone (161). The peptide is currently under development as an intranasal formulation for both male and female sexual dysfunction. It is a non-selective melanocortin receptor agonist, which in animals regulates sexual behavior including penile erection, sexual motivation, and in female rats, the secre-... 

The incidence of erectile dysfunction is low in men less than 40 years of age. It increases as men age, likely as a result of concurrent medical conditions that impair the vascular, neurologic, psychogenic, and hormonal systems necessary for a normal penile erection. 

Erectile dysfunction can result from any single abnormality or combination of abnormalities of the four systems necessary for a normal penile erection. Vascular, neurologic, or hormonal etiologies of erectile dysfunction are collectively referred to as organic erectile dysfunction. About 80% of patients with erectile dysfunction have the organic type. Patients who fail to respond to psychogenic stimuli have psychogenic erectile dysfunction. 

The goal of treatment is an improvement in the quantity and quality of penile erections suitable for intercourse. Simple as this may sound, health care providers need to ensure that patients have reasonable expectations for any therapies that are initiated. Furthermore, only patients with erectile dysfunction should be treated. Patients who have normal sexual function should not seek—or be encouraged to seek—treatment in an effort to enhance sexual function or enable increased activity. 

The primary therapeutic outcomes of specific treatments for erectile dysfunction include (1) improvement in the quantity and qnahty of penile erections suitable for intercourse and (2) avoidance of adverse drug reactions and drug interactions. 

Whereas prostatic carcinoma may be asymptomatic in patients with localized disease, most patients with signs and symptoms have advanced disease at presentation. In patients with locally invasive disease, the most common complaints arise from ureteral dysfunction or impingement. Patients complain of alterations in micturition manifested by urinary frequency, hesitancy, and dribbling.New onset impotence or less firm penile erections in an elderly male may indicate prostate cancer. 

Sildenafil citrate is a phosphodiesterase type 5 inhibitor that enhances the effect of nitric oxide by inhibiting phosphodiesterase type 5 in the corpus cavernosum of the penis. This results in vasodilation, increased inflow of blood into the corpora cavernosa, and ensuing penile erection npon sexnal stimulation. It is indicated in the treatment of impotence related to erectile dysfunction of the penis. 

As additional information about the physiological role of NO is accumulated, new ideas and strategies for the use of NO donors are emerging. For example, several studies have demonstrated the importance of NO in penile erection (Rajfer et al., 1992 Burnett et al., 1992), and it is possible that selective delivery of NO, through the use of NO donors, may improve erectile function in impotent men. Stief etal. (1992) have shown that intracavernosal injections of 0.1-1 mg of linsidomine in patients with erectile dysfunction produced dose-dependent erectile responses with no systemic or local side effects. Porst (1993) has also shown linsidomine injection to be useful in producing penile erection, but not as effective as injected prostaglandin Ei. Further studies to optimize NO delivery for erectile responses appear to be warranted. 

Other intracorporal agents used to induce penile erections include papaverine, a drug with a relaxant effect on smooth muscle, and phentolamine, an a-adrenergic receptor blocker. Yohimbine, an a2-adrenoreceptor antagonist, enhances noradrenergic neurotransmission and may improve erectile dysfunction via adrenergic system activation. 

Physiology of Penile Erection and Pathophysiology of Erectile Dysfunction... 

Vascular pathology may involve lesions of the inflow or outflow mechanisms of penile erection. Erectile dysfunction may be a manifestation of generalized atherosclerosis and may even be its initial presentation. Common risk factors associated with generalized penile arterial insufficiency include hypertension, hyperlipidemia, cigarette smoking, diabetes mellitus, and pelvic irradiation (Rosen et al. 1991). Less commonly, local stenosis of the conunon penile artery may occur in men who have sustained blunt pelvic or perineal trauma (Levine et al. 1990). 

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