What ED is ?
ED or impotence is defined as the consistent (lasting for at least six months) inability to achieve or maintain an erection that is satisfactory for sexual intercourse. The degree of ED may vary from a partial decrease in the rigidity of the penis to complete erectile failure. The term ED applies to problems associated with penile erection. It does not include problems associated with libido, ejaculation or orgasm.
How Common is ED ?
It affects millions of men worldwide and is quite common. A review of the epidemiological literature suggests that 5–20% of men suffer with moderate to severe forms of the disease, while data from an American community-based study indicate that 52% of men aged 40–70 years experience some degree of ED. In this study, the prevalence of ED increased with age, being around 39% in 40 year-old men and increasing to 67% in 70 year-old men.
What is the impact on patients?
Although ED is not life threatening, it has a dramatic impact on a man’s self-esteem, well-being (quality of life) and interpersonal relationships. It may lead to fear, loss of confidence and depression, and general dissatisfaction with life in general. In addition to its effect on sufferers, ED also has a significant impact on their partners. Thus, it is important to recognise the condition and give appropriate treatment. However, it is currently estimated that up to 70% of men with ED are not treated for their condition. The main reason for this is that only around 30% of men with ED seek medical advice. As awareness of the condition increases and it becomes less of a ‘taboo’ subject, the number of men seeking treatment for ED is expected to rise.
What is the main approach to treatment?
Over the last 15 years, several new treatments for ED have been introduced, including new pharmacological agents. These have significantly changed the way in which ED is managed. Nowadays, the recommended treatment approach is for the patient to choose the treatment that most closely meets his (and his partner’s) needs and preferences. Thus, the main role of the healthcare professional is to provide the patient with all the necessary information so that he can make an informed choice. The choice of treatments for ED is wide-ranging. For most men with the condition, oral therapy is the first-line treatment option. Second-line treatments, such as injection therapy, are indicated for patients who cannot use or fail to respond to first-line therapy.
ED of psychological origin
ED of psychological origin accounts for 10–20% of cases of ED. It tends to occur episodically. The patient usually experiences normal nocturnal or morning erections, and will probably still experience an erection in response to a fantasy or masturbation. The ED is likely to show a sudden onset, and may be preceded by a period of stress. Possible causes include anxiety about sexual performance, relationship problems, stress, depression, guilt and low self-esteem. There is a strong association between depression and ED. Schizophrenia is also associated with the condition, the main problem in this case being decreased libido.
ED of organic origin
Characteristically, ED of organic origin shows a gradual onset, starting with diminished firmness of the penis and a decrease in the frequency of erections. Attempts at intercourse may be unsuccessful during periods of stress or fatigue, and the patient may experience loss of nocturnal erections, poor morning erections and difficulty in masturbating. Libido is usually normal, but may decrease as the ED progresses. In general, any disorder or injury that affects the transmission of nervous impulses or impairs blood flow to the penis has the potential to cause ED.
Neurological causes
Neurological causes of ED include Parkinson’s disease, Alzheimer’s disease, multiple sclerosis, stroke, diabetic neuropathy (nerve damage) and cerebral trauma. These may cause a decrease in libido or may prevent the initiation of an erection. Injury to the spinal cord or pelvis may also cause ED, the extent of the condition depending on the extent and location of the injury. ED is also a common side effect of certain surgical procedures, such as radical prostatectomy (surgery for prostate cancer), which may damage the nerves that control penile erection and ejaculation.
Hormonal causes
Testosterone plays a major role in sexual function, and low serum testosterone levels (hypogonadism) can lead to a decrease in nocturnal erections and a decrease in libido. However, the patient is still likely to experience an erection in response to visual and sexual stimulation. Possible causes of low serum testosterone levels include testicular failure and hyperprolactinaemia (very high serum prolactin levels). The latter inhibit dopamine transmission in the CNS, leading to decreased production of gonadtrophin-releasing hormone, the hormone responsible for stimulating the release of testosterone from the testicles.
Vascular causes
Any disease or injury that affects the blood supply to the penis can cause ED. Diseases falling into this category include atherosclerosis (thickening of the arterial walls), hypertension, diabetes, hyperlipidaemia (very high serum cholesterol levels) and Peyronie’s disease (thickening of the fibrous connective tissue in the penis causing the penis to bend at an angle during erection). Perineal trauma (commonly caused by bicycling accidents), pelvic irradiation and smoking may also cause ED by affecting the penile blood supply.
Drug-induced ED
Many commonly used drugs may cause ED by disrupting the neurotransmitter pathways in the CNS that are involved in sexual function. Such drugs include:
- antidepressants
- antihypertensives
- histamine2-receptor antagonists (anti-ulcer drugs)
- statins (lipid-lowering drugs)
- opiates
- thiazide diuretics
- oestrogens
- some NSAIDs
- tranquillisers
- appetite suppressants
- alcohol.
Not all drugs within each class have this effect. For example, the antidepressant trazodone hydrochloride (Molipaxin) has been used with limited success as a treatment for ED, while the antidepressants sertraline hydrochloride (Lustral) and fluoxetine hydrochloride (Prozac) cause ED. If a patient experiences ED with a certain medication, it is reasonable to look for an alternative drug that does not cause the condition. Alcohol abuse causes ED by reducing libido. It also has a sedative effect on the neural pathways involved in penile function.
ED due to ageing
Sexual function decreases with increasing age, even in healthy men: the period between sexual stimulation and erection increases, erections are less firm, ejaculation is less forceful, the volume of ejaculation decreases, the penis becomes less sensitive to tactile stimulation, and serum testosterone concentrations decrease. In addition, certain diseases that are associated with ED are more prevalent among elderly men. These include diabetes, renal failure, angina, myocardial infarction and heart failure. Around 50% of men with diabetes have ED. Diabetes affects both the penile blood supply and the nerve terminals in the penis. Renal failure causes reduced libido and a decreased ability to have erections. This may be due to a number of factors associated with the disease, including low serum testosterone levels, poor penile blood flow, the use of multiple medications and psychological stress.
Possible organic causes of ED are summarised below.
- Neurological conditions, such as Parkinson’s disease and multiple sclerosisNeurological lumbar injuries
- Fracture of the pelvis
- Surgical procedures, such as perineal surgery, radical prostatectomy and vascular surgery
- Inflammation of the prostate, urethra or seminal vesicles
- Hormonal disorders, such as diabetes, gonadal failure, pituitary problems and thyroid problems
- Vascular disease
- Pelvic irradiation
- Smoking
- Use of certain medications, such as antihypertensives, diuretics, statins, histamine2-receptor antagonists, some NSAIDs, tranquillisers, and antidepressants
- Alcohol abuse
- Poor health, for example severe angina or shortness of breath
- Old age
Patient history
This is the most important aspect of the initial assessment as it will define the problem and provide clues as to the origin of the ED. It will also identify the patient’s needs and expectations, will highlight the need for any diagnostic tests, and will enable a decision to be made about whether to refer the patient. Questions should cover the patient’s medical, sexual and psychological history. The medical history should cover any disease states, medications, traumas and previous surgery. The sexual history should include questions about:
- past and present sexual relationships
- the patient’s current emotional status
- the onset and duration of the ED
- the quality of erotic and morning erections (in terms of rigidity and duration)
- any problems with arousal, ejaculation and orgasm
- any previous consultations and treatment.
The use of a validated questionnaire, such as the International Index of Erectile Function (IIEF), may help in taking the sexual history. This questionnaire helps to determine the severity of ED and can also be used to assess the efficacy of treatment. Finally, if the patient’s history suggests significant psychological problems (e.g. anxiety, depression, psychosis, alcoholism), these should be addressed before the ED is treated, and the patient should therefore be referred to a psychiatrist.
Physical examination
For most patients, only a basic examination is required. This should consist of taking blood pressure, auscultation of the heart, palpation of the abdomen (for a pulsatile mass), examination of the breasts and genitalia noting hair distribution (indicates hormonal abnormalities), and a rectal examination in patients over the age of 50 (to assess the state of the prostate gland and any problems with the penile autonomic nerve supply). While examining the genitalia, it is important to look for abnormalities in the size of the testicles, fibrosis in the shaft of the penis and any problems in retracting the foreskin.
Investigations
Further tests may be appropriate, depending on the patient’s history and the results of the physical examination. The majority of patients should undergo serum testosterone measurements. If levels of this hormone prove low, serum prolactin and luteinizing hormone (LH) levels should be determined to evaluate functioning of the hypothamamic-pituitary-gonadal axis. Patients who have not been previously tested for diabetes should also undergo blood glucose testing.
Other tests that may be considered include:
- full blood count
- dipstick urine analysis (to test for renal or hepatic impairment)
- standard serum chemistry to check renal function
- serum creatinine and electrolyte levels (to test for renal impairment)
- serum lipid profile (to test for hyperlipidaemia)
- serum prostate specific antigen levels (increased levels indicate a problem with the prostate gland)
- serum thyroid stimulating hormone (TSH) levels (to test for hypo- or hyperthyroidism)
- liver function tests (to test for hepatic impairment).
More specific tests that a specialist may advise include:
- assessment of the rigidity of nocturnal erections (nocturnal penile tumescence testing) to determine whether the ED has a psychological cause (nocturnal erections are normal in ED of psychological origin)
- neurological studies, such as testing the conduction velocity of the penile dorsal nerve or testing the latency of the bulbocavernosus reflex (anal sphincter contraction in response to squeezing the glans penis that gives an indication of the integrity of sacral nerve fibres)
- studies to evaluate the penile arteries, such as the use of Doppler ultrasound, penile plethysmography or the injection of vasoactive agents into the main chambers of the penis
- further studies of pituitary function, which may involve CT scanning of the brain.
When to refer ?
The following patients should always be referred:
- young patients who have always had erection difficulties
- patients with a history of pelvic/perineal trauma
- patients who show abnormalities of the testes or penis (e.g. Peyronie’s disease)
- patients in whom the results of initial screening tests are significantly abnormal
- patients with complicated psychological or psychosexual disorders
- patients with complex gonadal or other endocrine disorders
- patients with suspected brain or spinal cord disease
- patients with active CV disease
- patients requiring vascular or neurosurgical intervention (e.g. aortic aneurysm, lumbosacral disc diseas
Principles of treatment
The main aim in the management of ED is to determine the cause of the disease and to treat it where possible. The choice of treatment should be made by the patient (and partner). Thus, the role of the healthcare professional is to inform the patient about the treatment choices and to help the patient make a reasoned choice. The healthcare professional should:
- discuss the risks and benefits of the different treatment options
- ensure that the treatment chosen meets the patient’s needs and preferences
- agree on the goals of treatment before treatment starts
- give advice on how best to manage the chosen treatment and what to do if problems arise
- warn the patient about any potentially serious interactions between the chosen treatment and any currently used medications
- discuss and agree a plan for follow-up.
Patient education
Education of patients and their partners is an essential component in the management of ED. Communication with and education of the patient increases the likelihood that the patient will adhere to the chosen treatment. It also helps to clarify the patient’s treatment needs and expectations. The healthcare professional should therefore provide the patient with:
- a basic review of the anatomy and physiology of the erectile response
- an overview of the possible causes and associated risk factors (e.g. smoking, alcohol abuse, use of prescription drugs)
- the results of the initial assessment and any diagnostic testsa review of the treatment options, including the risks and benefits of each treatment.
Follow-up
Follow-up is an important part of the management process. A plan for follow-up should be discussed and agreed with the patient at the start of any treatment. Follow-up reviews should take place regularly between four weeks and six months after the start of treatment. Longer term follow-up will be required for patients receiving injection therapy to check for any signs of penile fibrosis. The follow-up reviews should be tailored to the needs of the patient and should evaluate the goals agreed at the start of treatment. They are also useful for:
- evaluating the progress of therapy
- re-evaluating the current treatment (e.g. changing the dose or the treatment itself)
- answering any concerns or queries the patient may have
- monitoring the patient’s general medical, sexual and psychological status.
Oral therapy
The main options for oral therapy are as follows:
- sildenafil (Viagra)
- tadalafil (Cialis)
- vardenafil (Levitra, Nuviva)
- apomorphine (Uprima)
All drugs have proved to be effective and well tolerated in the treatment of ED.
Sildenafil (Viagra)
Sildenafil (Viagra) was the first oral therapy to be approved by the US Food and Drug Administration (FDA) for the treatment of ED. Since its release in March 1998, it has become the drug of choice for most men with the erectile dysfunction. Sildenafil works by inhibiting phosphodiesterase type 5, an enzyme present in the penis that converts cyclic guanosine monophosphate (cGMP) to inactive 5-GMP. The inhibitory action of sildenafil causes levels of cGMP in the penis to rise. This enhances the effects of nitric oxide on the penile arterial system, leading to penile smooth muscle relaxation, vasodilatation and penile erection. However, this only occurs in the presence of sexual stimulation.
Sildenafil can be effective after 60 minutes in the presence of sexual stimulation, and it should therefore be taken 30–60 minutes before intercourse. Used in this way, it improves the erectile response in 50–88% of patients. It is important to bear in mind that sildenafil cannot initiate erections; it can only facilitate them. Thus, for sildenafil to be of any use, the patient must have some erectile function.
Dosing
The recommended dose of sildenafil is 25, 50 or 100 mg. All patients should start on a dose of 50 mg, and this can be decreased, maintained or increased depending on the response to the 50 mg dose and any associated side effects. The exception to this rule is patients with renal or hepatic failure, and patients over the age of 65 years. These patients should receive the lower 25 mg dose. Patients should not take more than one dose in any 24-hour period.
The tolerability of sildenafil has been evaluated in more than 3,700 patients, and the results have shown that the drug is well tolerated: side effects are predominantly mild and transient. The most common side effects experienced include headache (16%), facial flushing (10%), dyspepsia (7%), nasal congestion (4%) and blue–green colour blindness (3%). It also causes a small decrease in blood pressure. Hypersensitivity reactions (including rash), priapism, and painful red eyes have been reported.
Cautions
It should be used in caution in patients with:
- anatomical deformation of the penis (angulation, cavernosal fibrosis, Peyronie`s disease)
- a predisposition to prolonged erection (in sickle-cell anaemia, multiple myeloma, or leukaemia).
Contraindications
It is also contraindicated in patients receiving multiple drugs for the treatment of hypertension and in patients:
- taking nitrate therapy
- who have recently suffered myocardial infarction or stroke
- with active coronary ischaemia
- with congestive heart failure
- with borderline low blood pressure
- with borderline low cardiac volume status.
Tadalafil (Cialis)
Tadalafil (Cialis) is a new compound, which is a second-generation selective phosphodiesterase 5 (PDE-5) inhibitor. It is thought to have a much higher selectivity for the PDE-5 receptor, over and above the other subtypes of PDE.
Tadalafil has been shown to improve erections in 81% of men when compared to placebo. In some cases it can last for a 24-hour period. The dosing regimen is one tablet in a 24 hour period.
An important difference from sildenafil is that tadalafil can be taken both with and without food.
Dosing
The dose should be initially 10 mg taken 30 minutes to 12 hours before sexual activity. Further doses should be adjusted according to response (upto 20 mg as a single dose). Patients should be told that only one dose is necessary in 24 hours.
Cautions
As sildenafil.
Contraindications
As sildenafil.
Vardenafil (Levitra)
Vardenafil (Levitra, Nuviva) is a new selective phosphodiesterase type 5 inhibitor. You may like to read more about this drug by clicking here. It works in a similar way to the drugs mentioned above and has similar cautions and contraindications.
Apomorphine (Uprima)
Apomorphine (Uprima) is a dopamine D1 and D2 receptor agonist that works by enhancing dopamine neurotransmission in the hypothalamic neural pathways involved in initiating an erection. It has a quick onset of action, producing an erection within 18–19 minutes. The drug appears to be successful in up to 68% of patients. The recommended dose of apomorphine is 2 or 3 mg, and this is taken sublingually. The drug is well tolerated, and shows no interactions with other medications, food or alcohol. The most common adverse effects are nausea (observed in 2–16% of men), which is sometimes accompanied by vomiting, drowsiness and dizziness. These effects tend to be dose related and usually disappear with repeated exposure to the drug. However, the nausea experienced with apomorphine can limit patient compliance. To minimize the risk of adverse effects, all patients should start on a dose of 2 mg, and this dose should be used at least twice before trying the higher 3 mg dose. At the present time, apomorphine is indicated for patients with some degree of erectile function, younger patients, and those with mild to moderate ED. Studies to compare sildenafil and apomorphine are currently underway.
Hormone treatment
Testosterone replacement therapy aims to restore erectile function by restoring normal serum levels of testosterone. Such therapy is indicated only for patients with primary testicular failure (i.e. not secondary to other endocrine causes). Treatment may be given via intramuscular injections every two to three weeks or via daily transdermal patches: oral testosterone therapy is not recommended. If the patient has low testosterone levels caused by hyperprolactinaemia, the recommended treatment is bromocriptine mesylate (Parlodel).
Patients receiving testosterone replacement therapy should be monitored to ensure that they are responding to therapy, since this form of treatment is not always effective in the management of ED due to hypogonadism. Such treatment may also cause liver damage and stimulate growth of the prostate. Thus, patients should also be monitored for the development of liver or prostate disease. Testosterone replacement therapy is contraindicated in men with prostatism or a history of prostate carcinoma.
Vacuum devices
A vacuum device consists of a cylinder that is fitted over the penis. Air is pumped out of the device thus applying negative pressure to the penis and consequently drawing blood into it. The ‘erection’ is maintained by fitting a constriction ring around the base of the penis (Figure 2).
This form of treatment is suitable for a wide range of patients but success rates are very variable: a success rate of around 90% was reported in one study and 80% of patients continued with the device, while another study showed that only 23% of patients continued with the device after a 2-week trial and only 53% of these patients were satisfied with their treatment. Furthermore, another study showed that the ability to achieve an orgasm and overall satisfaction with this form of therapy was lower than with injection therapy (see next section).
The advantages of vacuum devices are that they are suitable for a wide range of patients including those in whom other therapies have been unsuccessful; they can be used long term; and the risk of adverse effects is low. The main adverse effects are penile pain, numbness and delayed ejaculation. Other disadvantages of vacuum devices are:
- they are contraindicated in patients with bleeding disorders
- they lack spontaneity and can be cumbersome to use
- pivoting may occur at the base of the penis
- the penis may feel cold to the partner.
Psychosexual therapy
Psychosexual therapy is a first-line treatment option for ED in any patient with significant psychological problems. It can be used alone or can be combined with physical treatments. Psychosexual therapy involves the therapist and patient working together to find out what is preventing the patient from experiencing a normal erection. Thus, the success of such treatment depends to a large extent on the attitude of the patient. A review of psychosexual therapy outcome studies showed that such therapy is successful in 50–80% of cases. However, long-term follow-up studies suggest that the rate of recurrence of ED after psychosexual therapy is high.
The advantages of psychosexual therapy are that it:
- is non-invasive
- can involve the patient’s partner
- can lead to long-term improvement in sexual function
- can improve communication between a couple
- can also address the partner’s problems.
The disadvantages of psychosexual therapy are that it is not available on the NHS in every area, the patient or partner may not be willing to undergo such treatment, it is time consuming, and success rates are variable.
Second-line treatments
You may like to read the resource text, which goes into greater depth on second- and third-line therapies for erectile dysfunction.
Intracavernosal injections
Drugs that have a vasodilatory effect on the penile blood supply and stimulate relaxation of the penile smooth muscle can be administered by direct injection into the main chambers of the penis to induce an erection. Drugs that may be administered in this way include alprostadil (prostaglandin E1), papaverine (a non-specific phosphodiesterase inhibitor) and phentolamine (an a adrenergic receptor antagonist). Phentolamine has minimal efficacy when given alone, but it potentiates the effects of alprostadil and papaverine. The most commonly used injection systems contain either alprostadil (e.g. Caverject and Edex) or a mix of alprostadil, papaverine and phentolamine (e.g. Tri-Mix).
Intracavernosal injections are suitable for a wide range of patients. The erectile response is rapid (5–15 minutes after injection), and the duration of the erection depends on the dose injected. Intracavernosal injections can be self-administered, but it is important that the patient receives appropriate training and education by medical personnel before being allowed to do this. The patient should administer no more than three injections per week and no more than one injection in any 24-hour period.
Intracavernosal therapy is effective in 60–90% of cases, and patient and partner satisfaction with such therapy is high: in one clinical study, 81% of ED sufferers and 90% of partners rated intercourse as satisfactory after twice weekly injections of alprostadil. Similarly, a six-month self-injection study with alprostadil showed that intercourse could be achieved after 94% of self-administered injections. The ED sufferers and their partners reported satisfactory intercourse after 87% and 86% of injections, respectively.
The main adverse effects associated with intracavernosal therapy include mild penile pain (after 11% of injections), prolonged erections (5% of men), penile fibrosis (1–20% of men) and persistent erections or priapism (1% of men). If a patient experiences a prolonged erection, the drug dose should be reduced for subsequent injections. Patients who experience an erection for more than four hours should seek medical attention as prolonged erections can cause scarring of the cavernosal tissue. Prolonged erections may be treated with intracavernosal injections of phenylepinephrine or epinephrine, or by the aspiration of blood from the corpora cavernosa.
Intracavernosal therapy is contraindicated in men with a history of hypersensitivity to the proposed drugs, those at high risk of priapism, those with sickle cell anaemia and those with severe psychiatric disorders, such as schizophrenia. A further disadvantage of therapy is that the user needs to have good manual dexterity and good eyesight. However, partners may be taught to administer the injections.
Transurethral therapy
Alprostadil can also be administered via the urethra in the form of a semi-solid pellet (the Medicated Transurethral System for Erection or MUSE™). The pellet should be inserted into the first 2–3 cm of the urethra after urination, as this lubricates the urethra and makes the pellet easier to insert. Under the supervision of a healthcare professional, the patient should first be challenged with a 500 ìg pellet. ‘Super responders’ should be switched to a lower dose of 125 or 250 ìg, while ‘under responders’ should receive a higher dose of 1000 ìg.
Transurethral therapy is suitable for a wide range of patients, including those who have a needle phobia. As with intracavernosal therapy, it can be self-administered. The satisfaction rate with transurethral therapy is around 70%. A further advantage of transurethral therapy is that it is associated with a lower risk of priapism than intracavernosal injections.
Disadvantages of transurethral therapy include:
- lower clinical success rate than with intracavernosal injections
- slower acting than intracavernosal injections
- mild penile pain in 10–29% of patients
- possible hypotension
- a high incidence of urethral pain or burning (in up to 30% of patients)
- possible vaginal discomfort for the partner
- requires manual dexterity, good eyesight and insertion after urination.
Third-line treatments
Penile prostheses
Penile prostheses are implants that can be surgically inserted into the penis enabling the penis to become erect. There are two types: malleable implants and inflatable implants. The malleable implants consist of paired rods, which are inserted into the corpora cavernosa and can be adjusted manually. Inflatable implants consist of paired cylinders that can be inflated using a small pump located under the skin of the scrotum.
Inflatable implants provide a more satisfying and cosmetic erection but are more likely to fail mechanically, are more likely to cause complications, and are more expensive than the malleable implants. Implants are suitable for patients with organic ED who fail to respond to pharmacological therapy or prefer a long-term solution to their condition. Success rates are high, and the patient satisfaction rate is around 80%. The main disadvantage of penile implants is that the internal structure of the penis is destroyed after their insertion. Thus, other treatment options will be ineffective if the implant has to be removed. Other disadvantages of penile implants include the need for surgery; a high risk of infection (2–16%); possible protrusion of the malleable implants; possible mechanical problems; perineal pain; and a high initial cost.
Vascular surgery
Vascular surgery for ED aims to increase blood flow to the corpora cavernosa by bypassing any arterial obstructions. Such revascularization is most successful in young patients (< 50 years of age) who have had pelvic or perineal trauma but have few vascular risk factors. In these patients, the long-term success rate can be as high as 60–70%. Revascularization is less successful in older men as they are more likely to have generalized arterial occlusive disease.
References
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Fugl-Meyer A R, Lodnert G, Bränholm I-B, Fugl-Meyer K S. On life satisfaction in male erectile dysfunction. Int J Impot Res 1997; 9: 141–8.
Kubin M, Wagner G, Fugl-Meyer A R. Epidemiology of erectile dysfunction. Int J Impot Res 2003; 15: 63–71.
Lue T F. Erectile dysfunction. N Engl J Med 2000; 342: 1802–13.
Montorsi F, Salonia A, Cestari A, Guazzoni G, Rigatti P, Stief C. Pharmacological management of erectile dysfunction. BJU International 2003; 91: 446–54.
Monga M, Rajasekaran M. Erectile dysfunction: current concepts and future directions. Arch Androl 2003; 49: 7–17.
Wespes E, Amar E, Hatzichristou D, Montorsi F, Pryor J, Vardi Y. Guidelines on erectile dysfunction. Eur Urol 2002; 41: 1–5.
Jordan G H. Erectile function and dysfunction. How it works and what can be done when it doesn’t. Postgraduate Medicine Online 1999; 105: 131–44.
Lue T F. Erectile dysfunction. N Engl J Med 2000; 342: 1802–13.
Monga M, Rajasekaran M. Erectile dysfunction: current concepts and future directions. Arch Androl 2003; 49: 7–17.
National Kidney And Urologic Diseases Information Clearinghouse. Erectile dysfunction. 2002.
Jordan G H. Erectile function and dysfunction. How it works and what can be done when it doesn’t. Postgraduate Medicine Online 1999; 105: 131–44.
Krane R, Goldstein I, Saenz de Tejada I. Impotence. N Engl J Med 1989; 321: 1648–59.
Lue T F. Erectile dysfunction. N Engl J Med 2000; 342: 1802–13.
Manecke R G, Mulhall J P. Medical treatment of erectile dysfunction. Ann Med 1999; 31: 388–98.
National Kidney And Urologic Diseases Information Clearinghouse. Erectile dysfunction.2002.
Padma-Nathan H. Diagnostic and treatment strategies for erectile dysfunction: the ‘process of care’ model. Int J Impot Res 2000; 12: S119–21.
Ralph D, McNicholas T for the Erectile Dysfunction Alliance. UK management guidelines for erectile dysfunction. BMJ 2000; 321: 499–503.
Wespes E, Amar E, Hatzichristou D, Montorsi F, Pryor J, Vardi Y. Guidelines on erectile dysfunction. Eur Urol 2002; 41: 1–5.
Padma-Nathan H. Diagnostic and treatment strategies for erectile dysfunction: the ‘process of care’ model. Int J Impot Res 2000; 12: S119–21.
Ralph D, McNicholas T for the Erectile Dysfunction Alliance. UK management guidelines for erectile dysfunction. BMJ 2000; 321: 499–503.
Jordan G H. Erectile function and dysfunction. How it works and what can be done when it doesn’t. Postgraduate Medicine Online 1999; 105: 131–44.
Krane R J, Goldstein I, Saenz de Tejada I. Impotence. N Engl J Med 1989; 321: 1648–59.
Manecke R G, Mulhall J P. Medical treatment of erectile dysfunction. Ann Med 1999; 31: 388–98.
Monga M, Rajasekaran M. Erectile dysfunction: current concepts and future directions. Arch Androl 2003; 49: 7–17.
Montorsi F, Salonia A, Cestari A, Guazzoni G, Rigatti P, Stief C. Pharmacological management of erectile dysfunction. BJU International 2003; 91: 446–54.
National Institute of Diabetes and Digestive and Kidney Diseases. Erectile dysfunction
Ralph D, McNicholas T for the Erectile Dysfunction Alliance. UK management guidelines for erectile dysfunction. BMJ 2000; 321: 499–503.
Wespes E, Amar E, Hatzichristou D, Montorsi F, Pryor J, Vardi Y. Guidelines on erectile dysfunction. Eur Urol 2002; 41: 1–5.
Efficacy and safety of tadalafil for the treatment of erectile dysfunction: results of integrated analyses. J Urol 2002 168(1332-6.
Jordan G H. Erectile function and dysfunction. How it works and what can be done when it doesn’t. Postgraduate Medicine Online 1999; 105: 131–44.
Krane R J, Goldstein I, Saenz de Tejada I. Impotence. N Engl J Med 1989; 321: 1648–59.
Monga M, Rajasekaran M. Erectile dysfunction: current concepts and future directions. Arch Androl 2003; 49: 7–17.
Montorsi F, Salonia A, Cestari A, Guazzoni G, Rigatti P, Stief C. Pharmacological management of erectile dysfunction. BJU International 2003; 91: 446–54.
National Institute of Diabetes and Digestive and Kidney Diseases. Erectile dysfunction.
Ralph D, McNicholas T for the Erectile Dysfunction Alliance. UK management guidelines for erectile dysfunction. BMJ 2000; 321: 499–503.
Wespes E, Amar E, Hatzichristou D, Montorsi F, Pryor J, Vardi Y. Guidelines on erectile dysfunction. Eur Urol 2002; 41: 1–5.
Ralph D, McNicholas T for the Erectile Dysfunction Alliance. UK management guidelines for erectile dysfunction. BMJ 2000; 321: 499–503.
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