Erectile response to transurethral alprostadil, prazosin and alprostadil-prazosin combinations

Intraurethral alprostadil for erectile dysfunction: a review of the literature

The global burden of erectile dysfunction (ED) is increasing. It is estimated that 8-19% of men in Europe have ED and that by 2025 the prevalence of ED worldwide will reach 322 million. The gold standard therapy for ED is an oral phosphodiesterase type 5 (PDE5) inhibitor, but they are not suitable for everyone; approximately 25% of patients do not respond to this therapy and it is contraindicated in others, e.g. those with vascular disease. When PDE5 inhibitors are not suitable, available options include intraurethral and intracavernosal alprostadil - a synthetic vasodilator chemically identical to the naturally occurring prostaglandin E(1) indicated for the treatment of ED. Intraurethral alprostadil is delivered by the Medicated System for Erection (MUSE).- a single-use pellet containing alprostadil suspended in polyethylene glycol administered using an applicator. It is recommended that intraurethral alprostadil be initiated at a dose of 500 μg, as it has a higher efficacy than the 250 μg dose, with minimal differences with regard to adverse events. Data from key clinical studies of intraurethral alprostadil show that it has a fast onset of effect and a good safety profile, with no occurrences of priapism, fibrosis (as seen with intracavernosal injection) or the typical systemic effects observed with oral ED pharmacological treatments. Intraurethral alprostadil has been associated with high patient preference, acceptance rates and quality of life versus intracavernosal injection due to its ease of administration. Evidence has shown that combination treatment with sildenafil may be a possible efficient alternative when single oral or local treatment has failed. Intraurethral alprostadil can be administered in all patients irrespective of ED origin and should be the first option in patients with ED for whom therapy with PDE5 inhibitors has failed or is contraindicated.

Mechanisms of penile erection and basis for pharmacological treatment of erectile dysfunction

Erection is basically a spinal reflex that can be initiated by recruitment of penile afferents, both autonomic and somatic, and supraspinal influences from visual, olfactory, and imaginary stimuli. Several central transmitters are involved in the erectile control. Dopamine, acetylcholine, nitric oxide (NO), and peptides, such as oxytocin and adrenocorticotropin/α-melanocyte-stimulating hormone, have a facilitatory role, whereas serotonin may be either facilitatory or inhibitory, and enkephalins are inhibitory. The balance between contractant and relaxant factors controls the degree of contraction of the smooth muscle of the corpora cavernosa (CC) and determines the functional state of the penis. Noradrenaline contracts both CC and penile vessels via stimulation of α₁-adrenoceptors. Neurogenic NO is considered the most important factor for relaxation of penile vessels and CC. The role of other mediators, released from nerves or endothelium, has not been definitely established. Erectile dysfunction (ED), defined as the "inability to achieve or maintain an erection adequate for sexual satisfaction," may have multiple causes and can be classified as psychogenic, vasculogenic or organic, neurologic, and endocrinologic. Many patients with ED respond well to the pharmacological treatments that are currently available, but there are still groups of patients in whom the response is unsatisfactory. The drugs used are able to substitute, partially or completely, the malfunctioning endogenous mechanisms that control penile erection. Most drugs have a direct action on penile tissue facilitating penile smooth muscle relaxation, including oral phosphodiesterase inhibitors and intracavernosal injections of prostaglandin E₁. Irrespective of the underlying cause, these drugs are effective in the majority of cases. Drugs with a central site of action have so far not been very successful. There is a need for therapeutic alternatives. This requires identification of new therapeutic targets and design of new approaches. Research in the field is expanding, and several promising new targets for future drugs have been identified.

Combination of alfuzosin and tadalafil exerts in vitro an additive relaxant effect on human corpus cavernosum

INTRODUCTION

Phosphodiesterase type 5 (PDE5) inhibitors, such as tadalafil, are a first-line treatment for erectile dysfunction (ED). Nevertheless, some patients do not respond to this treatment. Clinical data suggest that the addition of alpha1-adrenoceptor blocker, such as alfuzosin, commonly prescribed for lower urinary tract symptoms suggestive of benign prostatic hyperplasia, may be of benefit. Aim. Evaluation of the effect of alfuzosin, tadalafil or the combination of both on human corpus cavernosum.

METHODS

Human cavernosal tissues were obtained from 10 patients undergoing penile surgery. Strips contractility was studied in organ baths. Concentration-response curves to tadalafil were generated on norepinephrine (NE, 1-10 microM)-precontracted strips in the presence of alfuzosin or vehicle. Frequency-response curves (FRC) to electrical field stimulation (EFS, 0-64 Hz, 3 ms, 10 seconds, 300 mA) were generated in the presence of vehicle, alfuzosin, tadalafil, or both drugs combined. EFS (20 Hz, 1 ms, 10 seconds, 300 mM)-induced nitrergic relaxation on NE-precontracted strips was studied in the presence of vehicle, alfuzosin, tadalafil, or both drugs combined.

MAIN OUTCOME MEASURES

Functional measurement of cavernosal smooth muscle relaxation in the presence of tadalafil and alfuzosin.

RESULTS

The relaxation induced by tadalafil (10(-10) to 10(-5) M) on precontracted strips was enhanced by alfuzosin at both 10(-8) and 10(-7) M. The combination of alfuzosin (3.10(-8) M) and tadalafil (10(-7) M) was more efficient to inhibit FRC-induced contractions than each compound alone. The combination of tadalafil (10(-6) M) and alfuzosin (10(-8) M) increased the relaxation induced by EFS and its effect was greater than tadalafil alone. In addition, the combination of tadalafil (10(-6) M) and alfuzosin (10(-7) M) prolonged EFS-induced relaxation to a greater extent than each compound alone.

CONCLUSIONS

In vitro, the combination of alfuzosin and tadalafil is more efficient than each compound alone to relax adrenergic tone or to enhance nitrergic relaxation of the human corpus cavernosum. Such a combination deserves further investigation in placebo-controlled studies to evaluate its benefit in ED patients who are not sufficiently improved by PDE5 inhibitors.

Alprostadil for the treatment of erectile dysfunction

Erectile dysfunction (ED) is a common medical condition affecting over 20 m men in the United States. Efficacious medical therapy for the treatment of erectile dysfunction has been available since the early 1980s and can be divided into local pharmacotherapy and systemic therapy. Alprostadil, a synthetic form of prostaglandin E1, is a useful local pharmacotherapeutic agent for the treatment ED. Alprostadil is presently available for administration as an intracavernosal injection or an intraurethral suppository. Local alprostadil therapy is effective at restoring the ability to participate in intercourse in up to 70% of men with ED. The principle side-effects of alprostadil are local, with few systemic reactions. The mechanism of alprostadil, its efficacy in clinical trials and side-effects are examined to outline the utility of alprostadil for the treatment of ED.

Prostaglandin E1 for treatment of erectile dysfunction

BACKGROUND

Erectile dysfunction (ED), the inability to achieve or maintain an erection sufficient for satisfactory sexual activity, is one of the most common sexual dysfunctions in men. ED may have a dramatic impact on the quality of life of many men and their partners.

OBJECTIVES

The aim of this systematic review was to evaluate and summarise the effectiveness and safety of PGE1 in the treatment of erectile dysfunction.

SEARCH STRATEGY

We searched the Cochrane MS Group Trials Register (June 2003), the Cochrane Central Register of Controlled Trials (issue 2, 2003), MEDLINE (January 1966 - June 2003), EMBASE (January 1988 - June 2003) and reference lists of articles. We also undertook handsearching and contacting trialists and pharmaceutical companies.

SELECTION CRITERIA

All unconfounded, double blind, randomised controlled trials comparing PGE1 and placebo treatment in participants with ED of different aetiology were considered. Primary outcomes were: (a) patient and partner satisfaction measured by means of a self-assessment; (b) quality of life and (c) safety assessment. Both parallel group and cross-over design trials were considered for inclusion.

DATA COLLECTION AND ANALYSIS

All the reviewers independently selected articles for inclusion, assessed the trials' quality and extracted the data. Study authors were contacted for additional information.

MAIN RESULTS

Four trials involving 1.873 people, heterogeneous with respect to aetiology of ED, were included. Study design was two cross-over and two parallel group trials. Only the latter provided adequate data for meta-analyses. PGE1 was effective during follow-up in the "at least one successful intercourse" outcome (Peto Odds Ratio, OR 7.22, 95% CI. 5.68-9.18) and "number of successful intercourse/number of PGE1 administrations" (Peto Odds Ratio, OR 6.46, 95% CI. 5.95-7.01). One cross-over study reported "at least one successful intercourse" in 63.6% of participants with at least one dose of PGE1 (P < 0.01 for each active dose versus placebo). In the other cross-over study, only one of three treatment groups conducted a self-evaluation (55.5%: "good" or "excellent" response). Adverse effects were most frequent in the treated groups and occurred more often and intensely as doses increased. Penile pain (Peto OR 7.39, 95% CI. 5.40-10.12) and minor urethral trauma (Peto OR 3.79, 95% CI. 1.88-7.65) were predominant.

REVIEWERS' CONCLUSIONS

PGE1 was beneficial for many participants with ED of different aetiology. Adverse effects were proportional to dosage, albeit never serious. The use of PGE1 in ED could have been better interpreted if its effectiveness were compared by aetiology and with different forms of administrations, a longer follow-up were considered and more emphasis given to patient/partner relationships and quality of life.

Current oral treatments for erectile dysfunction

Erectile dysfunction (ED) is defined as the inability to achieve and maintain a penile erection adequate for satisfactory sexual intercourse. It is a significant male health problem of global dimensions affecting approximately 150 million men worldwide. A broad range of options are currently available for the management of ED. They include oral agents (phosphodiesterase 5 inhibitors, dopamine agonists and alpha-receptor blocking drugs), intracavernosal injection (papaverine, phentolamine, prostaglandin E1, vasoactive intestinal peptide), transurethral vasoactive agents (prostaglandin E1), vacuum erection devices, vascular surgery and penile prostheses. Here we review the physiology of penile erection and the currently available oral preparations. In addition, novel therapeutic strategies to improve erectile function are discussed.

Metachlorophenylpiperazine (m-CPP) induced intracavernous pressure responses in anaesthetized rats

Here we have recorded the effects of metachlorophenylpiperazine (m-CPP) on intracavernous pressure (ICP) in anesthetized rats pretreated with various pharmacological agents in an attempt to determine the mechanism and relevance of the m-CPP induced ICP response to other models of erection. m-CPP elicited consistent and significantly greater increases in ICP (71.5+/-6.6 mmHg) compared with the mixed 5-HT(2a/2c) agonists trifluoromethylphenylpiperazine (3.4+/-1.3 mmHg) and quipazine (10.9+/-1.8 mmHg). Blockade of 5-HT(2a) receptors with ketanserin failed to unmask any stimulatory effect of quipazine (7.2+/-1.0 mmHg). m-CPP induced ICP responses (71+/-7.0 mmHg) were unaffected in the presence of mianserin (63+/-5 mmHg) and ketanserin (51+/-12 mmHg). Spiperone significantly reduced the m-CPP induced increase in ICP (8.0+/-1.0 mmHg). Naloxone, yohimbine and 8-hydroxy-2-(di-n-propylamino)tetralin (8-OHDPAT) failed to elicit increases in ICP on their own. All three drugs significantly reduced the latency to the first m-CPP induced ICP response compared to saline. Yohimbine increased the duration of m-CPP induced ICP responses whereas 8-OHDPAT increased the mean number of m-CPP induced ICP responses compared to saline. The effects of m-CPP on ICP in anesthetized rats may not be mediated by 5-HT(2c) receptors and appears to be similar to erection in copula, but not erection elicited by other drugs or penile sheath retraction.

Male sexual function and its disorders: physiology, pathophysiology, clinical investigation, and treatment

This review is designed to help the reproductive endocrinologist integrate his or her professional activity with those of other disciplines including urology, radiology, neurology, and psychology in order to successfully manage all of the inseparable aspects of male sexual and reproductive functioning. Significant advances in the field of male sexual physiology and pathophysiology and new methods of investigation and treatment of male sexual disorders are outlined. The review synthesizes available data on the following: norms of sexual organs, aging and sexuality, role of central and peripheral neurochemicals in each stage of the sexual cycle, role of corporeal smooth muscles in the hemodynamic control of erection and detumescence, influence of psychological factors, drugs, and disease on all aspects of sexual functioning, and use of nocturnal penile tumescence monitoring, imaging investigations, and neurophysiologic studies in the diagnostic workup of males with sexual dysfunction. Clinical algorithms are presented where appropriate. Extensive discussions on newly developed strategies in psychological and behavioral counseling, drug therapy, tissue engineering, nonsurgical devices, and surgical treatments for all forms of sexual disorders are also provided. Lastly, the effect of sexual dysfunction and its treatment on quality of life in affected men is addressed, along with recommendations for future research endeavors.

Intracavernous injections: still the gold standard for treatment of erectile dysfunction in elderly men

The objective of this work was to determine the effectiveness of intracavernous injections (ICI) of vasoactive drugs in elderly men with erectile dysfunction and to compare the results obtained with the injection of two different drug combinations. It was a case control study. The sample consisted of 300 men, 63-85 y of age (mean 67.1) with erectile dysfunction of organic origin. Among the patients 180 underwent first trial with injection of prostaglandin E1 (PE). Further on these 180 patients and another 120 (in total 300 patients) were treated with a triple combination of papaverine hydrochlorate, phentolamine messylate and prostaglandin E1 (PPR). The number of responders to the injection of either PE alone or the drug combination was recorded. The quality of the erections was evaluated in the outpatient clinic by the medical staff and through patient's report after home trial. The average volume of either PE or PPR necessary to obtain a functional erection was measured. We observed a statistically significant association between the results obtained after the injection of PPR as compared to PE (chi2 with 2 d.f.: 34.666; P= < 0.001). A functional erection was obtained in 224/300 (74.7%) after the injection of PPR as compared to 87/180 men (48.3%) treated with PE. The average volume of PPR necessary to obtain a functional erection was 0.35+/-0.14 ml whereas that of PE was 1.3+/-0.3 ml. intracavernous injection of vasoactive drugs is still one of the most successful therapies for patients suffering from organic impotence. It is less effective in the older age group as compared to younger. However, if this form of therapy is chosen for aged men the triple combination therapy (PPR) yields a higher response rate than that obtained with prostaglandin alone.

Intracavernosal injection and intraurethral therapy for erectile dysfunction

Although the search for newer and more effective oral therapies is continually expanding, intracavernosal and intraurethral treatments continue to keep pace and are expected to remain in the clinician's armamentarium in the years to come. Unless there are contraindications, oral therapies are effective, have minimal side effects, and are first-line treatment. Some patients who have failed intraurethral and intracavernosal injection therapies previously have been shown to have successful outcomes with oral sildenafil in 56% to 57% of cases. If oral therapies are ineffective or have undesirable side effects, the intraurethral or intracavernosal routes are the next approach that should be prescribed.

Optimizing the therapeutic approach of transurethral alprostadil

OBJECTIVE

To investigate the efficacy and safety of two different starting doses of transurethral alprostadil (250 microg and 500 microg, MUSE, Vivus Inc., Menlo Park, CA, USA, and Astra Läkemedel AB, Södertälje, Sweden) and the need for dose titration in a general population with erectile dysfunction.

PATIENTS AND METHODS

In a 12-week randomized and open multicentre study with parallel groups, 166 patients were randomised to a starting dose of either 250 or 500 microg of MUSE and evaluated for safety. Of these patients, 142 were included in the analysis of efficacy. MUSE marked in four doses (125, 250, 500 and 1000 microg) was supplied and during the trial the dose could be increased or decreased step-wise until a satisfactory response was attained. The efficacy was assessed using the Erection Assessment Scale (EAS), as coitus (by diary) and the International Index of Erectile Function.

RESULTS

The lowest dose of MUSE with which the patients achieved at least one EAS score of 4 or 5 was 125 microg for 1% of participants, 250 ++microg for 27%, 500 microg for 32%, 1000 microg for 6%, and finally 1000 microg plus a pubic band for 8%. Thirty-five of the 142 patients (25%) did not report an EAS of 4 or 5. Most patients (> 60%) achieved an EAS of 4 or 5 on the lower doses (125, 250 and 500 microg). Almost all patients who had an EAS score of 4 or 5 also had intercourse. In all, 68% reported sexual intercourse at least once in course of the study. More patients reported penile pain while treated with 500 microg than with 250 microg (P < 0.05) during the first 4 weeks. However, the penile pain was severe in very few men and it was a minor problem. Hypotensive symptoms were reported six times, independently of dose level. The administration of MUSE was generally rated as comfortable. No patients reported urethral stricture, penile fibrosis, or priapism either in the clinic or at home.

CONCLUSION

Recommending 500 microg as a starting dose increased the percentage of patients reporting at least one EAS of 4-5, with or without sexual intercourse, from 28% to 60%. No serious dose-related systemic effects were seen. When starting on 500 microg, patients were more likely to find directly the dose that gave sufficient response and treatment satisfaction. We suggest that the appropriate starting dose of MUSE should be 500 microg.

Pharmacological treatment of erectile dysfunction

There is growing evidence that the field of pharmacotherapy, particularly oral drugs, will be dominant in the future management of sexual dysfunction. Basic research has led to the understanding of the intracellular mechanisms that control penile smooth muscle contractility and therefore erection, opening a vast area for pharmacological intervention. Moreover, the importance of central neurohormonal mechanisms has made these pathways the target for new centrally acting drugs. Given these trends most patients suffering from erectile dysfunction will respond to pharmacological agents in the not so distant future.

Pharmacotherapeutic advances in the treatment of erectile dysfunction

An estimated 20 million to 30 million American men have erectile dysfunction (ED). The past 2 decades of research defining erectile physiology and investigating the pathogenesis of ED have led to the recognition of a predominantly vascular basis for organic male sexual dysfunction. These scientific advances have laid the foundation for the advent of pharmacotherapies. The Food and Drug Administration approval of intracavernosal, intraurethral, and oral pharmacotherapeutics for ED has revolutionized non-surgical management of this condition. The primary care physician is faced with the challenges of diagnosis and treatment of ED, as well as referral of patients to urologists. In this article, erectile physiology and pathophysiology are reviewed, and pharmacotherapeutics are classified and discussed by their mechanisms of action and the means of administration. A thorough understanding of these new therapeutic options is key to the accurate diagnosis and successful treatment of ED and maximal patient satisfaction and care.

Current concepts in the management of post‐radical prostatectomy impotence

Erectile dysfunction after radical retropubic prostatectomy has a multifactorial aetiology, including both neurogenic and vasculogenic factors. Postoperative potency is improved with preservation of the neurovascular bundles in a nerve-sparing procedure. Preoperative and intraoperative identification and preservation of accessory pudendal arteries may also improve postoperative potency rates. The early institution of treatment with intracavernous alprostadil appears to improve postoperative potency rates. Treatment with newer therapeutic agents, such as Sildenafil and Invicorp, are both efficacious and well tolerated.

Opportunities for the treatment of erectile dysfunction by modulation of the NO axis--alternatives to sildenafil citrate

Erectile function in man depends upon a complex interaction of psychogenic, neurologic, hormonal and vascular factors, and therefore the management of erectile dysfunction (ED) reflects this complexity of control. Therapeutic options include psychological and non-pharmacological approaches as well as drug treatments. The effectiveness of the type-5 cGMP phosphodiesterase inhibitor sildenafil citrate (Viagra) confirms the pivotal role of the NO-cGMP axis in promoting and maintaining erection. Although widely acclaimed, sildenafil leaves many questions unanswered, especially regarding its susceptibility to pharmacokinetic drug interactions, and its safety in patients with ischaemic heart disease and those taking nitrates. In view of the epidemiological link between erectile dysfunction and cardiovascular disease in the elderly, this limitation might have much broader implications. The presently available scientific documentation, although less extensive, indicates that NO donors, such as topically applied nitroglycerin (GTN; for example, 1-2 puffs of an ordinary GTN spray applied to the shaft of the penis), might be a reasonable alternative. Further larger-scale research on the efficacy and tolerability of topical GTN is needed to establish its full therapeutic potential in the treatment of erectile dysfunction.