Pharmacokinetics of vasoactive substances administered into the human corpus cavernosum

Development of a novel topical formulation of glyceryl trinitrate for the treatment of erectile dysfunction

Erectile dysfunction (ED), defined as the inability to initiate or maintain an erection sufficient for satisfactory sexual intercourse, is common, particularly in men aged ≥50 years. Existing treatments have significant limitations, and there remains a need for a fast-acting (to facilitate spontaneity during intercourse) and well tolerated local therapy. Topical glyceryl trinitrate (GTN) may meet this need because GTN undergoes rapid metabolism in penile smooth muscle and endothelial cells to produce nitric oxide, which plays a key role in the development of erection. This paper describes the rationale for the development of MED2005, a topical GTN formulation using DermaSys® technology, which is undergoing clinical trials for the treatment of ED. Pharmacokinetic studies have shown that MED2005 provides rapid delivery of GTN following application to the glans penis, and a Phase 2(a) trial in men with ED showed that MED2005 produced significant improvements in erectile function, compared with placebo. MED2005 was well tolerated in this trial, with only 21 cases of headache in 1003 intercourse attempts. It is anticipated that MED2005 will provide an effective therapy for ED, with a fast onset of action, good local tolerability, and fewer contraindications than phosphodiesterase 5 inhibitors, the current cornerstone of ED therapy.

Topical Alprostadil for the Treatment of Female Sexual Arousal Disorder

Female sexual dysfunction is a common disorder that is present in over 40% of women in the USA. An evaluation of female sexual dysfunction differs greatly from male erectile dysfunction in that female sexual dysfunction is a very general term that encompasses a variety of sexual complaints in women, rather than a specific physiological disorder. No pharmacological treatment is presently approved for the treatment of the myriad of disorders that are involved in female sexual dysfunction. One of the more common disorders of female sexual dysfunction involves disturbances in objective or subjective sexual arousal. Sexual arousal in women has a central component and a peripheral, or vulvar, component. Disorders in vulvar blood flow and stimulation may lead to decreased genital and central arousal. A logical corollary of this statement is that an improvement in local blood flow by the use of a local or systemic vasodilator may lead to an increase in overall sexual arousal and an increase in sexual satisfaction. This article will explore the use of topical alprostadil as a local vasodilator to improve sexual arousal and sexual satisfaction in women with female sexual arousal disorder.

Erectile Dysfunction

Erectile dysfunction has been defined by the National Institutes of Health as the inability to achieve and/or to maintain an erection for satisfactory sexual intercourse. It may result from psychological or organic causes. With the advent of oral pharmacotherapy, the diagnostic approach has significantly changed over the past decade. The number of patients examined at the radiology clinics has also been decreased. However, evaluation by imaging modalities, such as color Doppler ultrasound, cavernosography, and angiography, still remains the cornerstone of the diagnostic workup of the patients with erectile dysfunction. The aim of this review was to focus briefly on the penile anatomy, the pathophysiology of erection, and radiological techniques for investigating vascular causes of erectile dysfunction and findings on different radiological methods.

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.

In vitro viability of human cavernosal endothelial and fibroblastic cells after exposure to papaverine/phentolamine and prostaglandin E1

OBJECTIVE

To investigate the influence of commercially available vasoactive drugs on human cavernosal endothelial and fibroblastic cells in vitro, as although corporal fibrosis is a well known side-effect of intracavernosal injection therapy for erectile dysfunction, the possible detrimental effect of these agents on the endothelium lining the cavernosal vascular spaces is uncertain.

MATERIALS AND METHODS

Cultured primary endothelial (13) and fibroblastic cells (12), obtained from potent patients undergoing penile surgery, were exposed to different physiological dilutions of prostaglandin E1 (PGE1), papaverine/phentolamine or the respective triple-mix of these agents for 30 min. Viable cells were counted and cell metabolic activity measured in these cultures 48 h after drug exposure.

RESULTS

There was a significant dose-dependent decrease in the viable cell count after exposure to papaverine-containing formulations, probably because of the low pH of this substance. This cytotoxic effect was more pronounced in endothelial than in fibroblastic cells, and was not apparent in the PGE1 groups. The relative increase in cell metabolic activity in cultures affected by a moderate cytotoxic effect indicated a regenerative process.

CONCLUSION

These comparative results in endothelial and fibroblastic cell cultures suggest that the endothelium rather than the interstitium of the corpus cavernosum is more sensitive to side-effects produced by intracavernosal injection therapy with papaverine. Thus, unfavourable consequences on the function of the endothelial layer might be as important as the risk of interstitial fibrosis. As these effects were not detected for PGE1 this drug should be preferred to papaverine in clinical practice.

Cytotoxicity of different intracavernous vasoactive drugs on cultured endothelial cells of human corpus cavernosum penis

OBJECTIVES

To investigate the cytotoxic effect of prostaglandin E(1) (PGE(1)), a standard combination of papaverine/phentolamine, and a triple mixture of these agents on human cavernosal endothelial cells using a cell culture model. The endothelial layer of the corpus cavernosum plays an important role in signal transduction of penile erection and is directly exposed to vasoactive agents after intracavernous injection for erectile dysfunction.

METHODS

Primary endothelial cells were obtained from the corpus cavernosum of 13 potent patients undergoing penile surgery. Cultured cells were exposed for 30 minutes to physiologic dilutions of 20 microg PGE(1), 30 mg papaverine/1 mg phentolamine, or the same dosages of the triple mixture of these agents, each dissolved in 5 to 50 mL sodium chloride. Lactate dehydrogenase release as a cytotoxicity marker was measured 6 hours after drug exposure, and the total cell metabolic activity was quantified after 48 hours with a 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxy-phenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS)-based assay. Additionally, the amount of viable cells was identified with a dual fluorescent staining procedure.

RESULTS

The initial release of lactate dehydrogenase was elevated up to 3.2-fold in the concentrated papaverine/phentolamine and triple mixture group compared with PGE(1) and the control. After 48 hours, the papaverine-containing formulations led to a significant dose-dependent decrease in the viable cell count and metabolic activity of the cultures that was not noticed with PGE(1).

CONCLUSIONS

These in vitro data strongly suggest an unfavorable effect of vasoactive agents containing papaverine on cavernosal endothelial cells. Before fibrotic changes of the smooth muscle stroma, the functionally important endothelium of the corpus cavernosum might suffer significantly from intracavernous injection therapy. Therefore, papaverine should no longer be used for this indication.

Colour Doppler ultrasound of the penis

Because it is a superficial structure, the penis is ideally suited to ultrasound imaging. A number of disease processes, including Peyronie's disease, penile fractures and penile tumours, are clearly visualized with ultrasound. An assessment of priapism can also be made using spectral Doppler waveform technology. Furthermore, dynamic assessment of cavernosal arterial changes after pharmaco-stimulation allows diagnosis of arterial and venogenic causes for impotence. This pictorial review illustrates the range of diseases encountered with ultrasound of the penis.

The epidemiology, anatomy, physiology, and treatment of erectile dysfunction in chronic renal failure patients

Erectile dysfunction (ED) is an associated morbidity for men with chronic renal failure. An understanding of the epidemiology, anatomy, physiology, and treatment options for ED can greatly improve the quality of life for men with chronic renal failure. There are psychological and physiological causes for erectile dysfunction. Once the key features leading to the patient's loss of potency have been identified, appropriate treatment plans can be instituted, often with successful outcomes. The purpose of this article is to assist the nephrology interdisciplinary team in the management of ED by reviewing possible causes, available studies, and treatment options for their patients.

Simultaneous determination of prostaglandin E1, prostaglandin E0 and 15-keto-prostaglandin E0 in human plasma by gas chromatography/negative-ion chemical-ionization tandem mass spectrometry

A sensitive and selective routine method for the simultaneous determination of prostaglandin E1 (PGE1), prostaglandin E0 (PGE0) and 15-keto-prostaglandin E0 (15-keto-PGE0) in human plasma is described using deuterated internal standards. The analytes were isolated from acidified human plasma by solid-phase extraction by means of Bond Elut C18 cartridges and derivatized to the pentafluorobenzyl (PFB) ester methoxime. The analytes were purified on Bond Elut Si cartridges and converted to the trimethylsilyl (TMS) ether. Quantitation was achieved by gas chromatography-negative-ion chemical-ionization tandem mass spectrometry. The precursor ion [M-PFB]- = [P]- carried more than 80% of the total ion current. Collision activated decomposition (CAD) of [P]- resulted in characteristic product ions of which the [P-2(CH3)3SiOH]- ion (PGE1) and the [P-(CH3)3SiOH]- ion (PGE0 and 15-keto-PGE0) were used for quantitation. The lower limit of quantitation (LLQ) was 2 pg/ml (PGE1 and PGE0) and 10 pg/ml (15-keto-PGE0) extracted from 2 ml of human plasma. Linear calibration curves were obtained over the concentration range 2-100 pg/ml (PGE1 and PGE0) and 10-500 pg/ml (15-keto-PGE0). In all cases, the precision and accuracy were < 17%. The present method has been applied successfully to pharmacokinetic and clinical studies in humans.

Hepatotoxicity related to intracavernous pharmacotherapy with papaverine

OBJECTIVES

To determine the incidence of hepatotoxicity related to self-administration of intracavernous papaverine or papaverine/phentolamine (bimix).

METHODS

From October 1994 through June 1996, we retrospectively reviewed the medical records of 71 consecutive patients diagnosed with organic erectile dysfunction (ED) and receiving intracavernous injection therapy. Inclusion criteria were documentation of normal baseline liver function tests (LFTs), a minimum of 6 months of follow-up that included LFTs, at least one self-injection every 2 weeks, and no other prior or concurrent treatment for ED. Thirty evaluable patients satisfied the inclusion criteria and formed group 1. Mean age was 63 years (range 40 to 77), mean follow-up was 18 months (range 6 to 32), and mean number of injections per month was 5.7 (range 3 to 12). An age-matched population of 20 patients (mean age 69 years, range 46 to 90) without ED but with similar comorbid risk factors formed the control group (group 2). All patients in group 2 had routine long-term follow-up of LFTs (mean 52 months, range 10 to 1 14).

RESULTS

Two patients (6.67%) from group 1 had elevated LFTs during treatment: one experienced a mild elevation in alanine aminotransferase and the other developed transient elevations of total bilirubin and aspartate aminotransferase 6 months after beginning therapy. Both patients reported a history of alcohol abuse. Both patients remained asymptomatic. Neither patient required discontinuation of therapy. One patient (5%) from group 2 developed an elevation of total bilirubin at a follow-up of 12 months.

CONCLUSIONS

Routine monitoring of LFTs is probably unnecessary during intracavernous pharmacotherapy. Patients with a history of alcohol abuse or liver disease, however, should be followed up more closely when papaverine is selected for intracavernous injection. In these patients, LFTs should be obtained before initiating treatment and at 6-month intervals.

Effects of intracavernous calcium channel blockers in dogs

Intracavernous injection of smooth muscle relaxing agents can induce penile erection. In this experimental study, we compared the effects of intracavernously injected calcium channel blockers (CCBs) and papaverine in dogs, and investigated their clinical applicabilities. We administered 30 mg papaverine, 10 mg nifedipine, 10 mg nitrendipine and 2.5 mg verapamil to 10 adult male dogs intracavernously, each at different times. Intracavernous pressure values, systemic arterial pressure values and heart rate values were recorded for 45 minutes after the intracavernous injections. We used the paired Student t-test for statistical analysis. Papaverine induced full erection in all of the 10 dogs. Nifedipine induced full erection in 4, nitrendipine in 5, and verapamil in 6 of the 10 dogs. Nifedipine and nitrendipine caused significant decreases in blood pressure and increases in heart rate. In conclusion, the effects of intracavernous CCBs are not superior to those of papaverine. We cannot recommend nifedipine and nitrendipine for intracavernous injection, but verapamil may be included in intracavernous pharmacotherapeutic combinations.

Influence of the method of intracavernous injection on penile rigidity: a possible pharmacokinetic explanation

OBJECTIVES

To study whether the method of intracavernous injection of vasodilators has an effect on the clinical outcome and to explain the mechanism of possible influence.

METHODS

In an open clinical study, penile rigidity after bolus injection was compared with rigidity after slow injection in 52 self-injecting, impotent patients. In 35 volunteers, venous plasma levels of intracavernosally injected drugs were followed under different injection conditions: slow injection of undiluted drug, slow injection of diluted drug, bolus injection, use of a tourniquet, or slow injection followed by squeeze of the corpora.

RESULTS

Of the 52 patients, 28 reported better penile rigidity after a bolus injection than after slow injection of vasodilators. The other 24 reported no difference in rigidity. Systemic side effects did not occur, but 4 patients reported local pain after bolus injection. In the 35 volunteers, the lowest plasma levels were observed when a tourniquet was used or when a bolus injection was performed; the quickest transfer was observed after a slow injection of a low volume of the drug.

CONCLUSIONS

Better rigidity was observed after bolus injection in a majority of the patients using the same dose of vasodilators. This could be due to the pharmacokinetic phenomenon of a slower drug transfer to the systemic circulatory system after a bolus than after a slow injection.

Treatment of men with erectile dysfunction with transurethral alprostadil. Medicated Urethral System for Erection (MUSE) Study Group

BACKGROUND

Erectile dysfunction in men is common. We evaluated a system by which alprostadil (prostaglandin E1) is delivered transurethrally to treat this disorder.

METHODS

Alprostadil was delivered transurethrally in a double-blind, placebo-controlled study of 1511 men, 27 to 88 years of age, who had chronic erectile dysfunction from various organic causes. The men were first tested in the clinic with up to four doses of the drug (125, 250, 500, and 1000 microg); those who had sufficient responses were randomly assigned to treatment with either the effective dose of alprostadil or placebo for three months at home.

RESULTS

During in-clinic testing, 996 men (65.9 percent) had erections sufficient for intercourse. Of these men, 961 reported the results of at least one home treatment; 299 of the 461 treated with alprostadil (64.9 percent) had intercourse successfully at least once, as compared with 93 of the 500 who received placebo (18.6 percent, P<0.001). On average, 7 of 10 alprostadil administrations were followed by intercourse in men responsive to treatment. The efficacy of alprostadil was similar regardless of age or the cause of erectile dysfunction, including vascular disease, diabetes, surgery, and trauma (P<0.001 for all comparisons with placebo). The most common side effect was mild penile pain, which occurred after 10.8 percent of alprostadil treatments, but the pain rarely resulted in refusal to continue in the study. Hypotension occurred in the clinic in 3.3 percent of men receiving alprostadil. Hypotension-related symptoms were uncommon at home. No men had priapism or penile fibrosis.

CONCLUSIONS

In men with erectile dysfunction, transurethral alprostadil therapy resulted in erections in the clinic and in intercourse at home.

Anxiety-induced failure in erectile response to intracorporeal prostaglandin-E1 in non-organic male impotence: a new diagnostic approach

Intracavernous injection (ICI) of prostaglandin-E1 (PGE1) is used widely as the first diagnostic test in the study of erectile dysfunction. However, a lack of full erection after a maximal dose is frequent. As well as vascular incompetence, this may be due to stress-induced changes, related to the ICI procedure. The aim of this study was to investigate the influence of emotional disturbances on erectile response to ICI in impotent patients. Initially, 24 young men with non-organic impotence (age 34.6 +/- 1.5 years; mean +/- SEM) were selected and randomized single-blind to pharmacoerection with PGE1 alone (20 micrograms/mL) or a mixture (cocktail) containing 20 micrograms PGE1 plus an alpha-adrenergic receptor blocker, phentolamine (Phe, 0.5 mg/mL). Additional studies were also performed double-blind on 10 men with non-organic impotence (age 37.6 +/- 1.2 years) utilizing higher PGE1 dosages for ICI (25 micrograms/mL alone or in combination with Phe, 0.5 mg/mL). After a 7-day interval, all subjects were crossed-over to receive the alternative treatment. The presence of emotional disturbances was assessed in all patients by the administration of rapid tests (Stai-X1 and Stai-X1r for state-anxiety before and after ICI, respectively; Stai-X2 for trait-anxiety; Zung-test for depression) at the first and at the remaining (Stai-X1 and Stai-X1r) ICI sessions. ICI with 20 and 25 micrograms/mL PGE1 led to a comparable percentage of patients who reported a valid-for-intromission (VFI) erection (63 and 60%, respectively). In contrast, use of the cocktails significantly increased the percentage of subjects with a VFI (87 and 90% of the total number of patients tested, respectively; p < 0.05). Moreover, a strong inverse correlation between state-anxiety scores (Stai-X1) and the erectile response to ICI with 20 and 25 micrograms PGE1 was found (r = -0.69, p < 0.001); such a correlation was not present in patients who underwent ICI with the cocktails. Two cases of prolonged erection occurred (one after 20 micrograms PGE1 and the other after 20 micrograms PGE1 plus Phe) which were reversed promptly by the intracavernous injection of metharaminol. It is concluded that the lack of a full erectile response after ICI with PGE1 can be related to the presence of a high 'state-anxiety' in the patients. In such patients, a VFI erectile response can be induced by the administration of a cocktail test-dose.