Effect of moxisylyte hydrochloride on isolated human penile corpus cavernosum tissue

A comprehensive history of injection therapy for erectile dysfunction, 1982-2023

INTRODUCTION

Although oral phosphodiesterase 5 inhibitors represent a first choice and long-term option for about half of all patients with erectile dysfunction (ED), self-injection therapy with vasoactive drugs remains a viable alternative for all those who are not reacting or cannot tolerate oral drug therapy. This current injection therapy has an interesting history beginning in 1982.

OBJECTIVES

To provide a comprehensive history of self-injection therapy from the very beginnings in 1982 by contemporary witnesses and some members of the International Society for Sexual Medicine's History Committee, a complete history of injection therapy is prepared from eyewitness accounts and review of the published literature on the subject, as well as an update of the current status of self-injection therapy.

METHODS

Published data on injection therapy, as a diagnostic and therapeutic tool for ED, were reviewed thoroughly by PubMed and Medline research from 1982 until June 2023. Early pioneers and witnesses added firsthand details to this historical review. Therapeutic reports of injection therapy were reviewed, and results of side effects and complications were thoroughly reviewed.

RESULTS

The pioneers of the first hours were Ronal Virag (1982) for papaverine, Giles Brindley (1983) for cavernosal alpha-blockade (phentolamine and phenoxybenzamine), Adrian Zorgniotti (1985) for papaverine/phentolamine, and Ganesan Adaikan and N. Ishii (1986) for prostaglandin E1. Moxisylyte (thymoxamine) was originally marketed but later withdrawn. The most common side effect is priapism, with the greatest risk of this from papaverine, which has modified its use for therapy. Currently, prostaglandin E1 and trimixes continue to be the agents of choice for diagnostic and therapeutic use in ED. A recent agent is a mixture of a vasoactive intestinal polypeptide (aviptadil) and phentolamine.

CONCLUSIONS

After 40 years, self-injection therapy represents the medication with the highest efficacy and reliability rates and remains a viable option for many couples with ED. The history of this therapy is rich.

Long-term oral treatment with BAY 41-2272 ameliorates impaired corpus cavernosum relaxations in a nitric oxide-deficient rat model

OBJECTIVE

• To investigate the potential beneficial effects of 4-week oral treatment with 5-cyclopropyl-2-[1-(2-fluoro-benzyl)-1Hpyrazolo[3,4-b]pyridin-3-yl]-pyrimidin-4-ylamine (BAY 41-2272), a nitric oxide (NO)-independent soluble guanylate cyclase activator, on impaired rat corpus cavernosum relaxations in NO-deficient rats.

MATERIAL AND METHODS

• Male Wistar rats were divided into four groups: Control, N (G)-nitro-L- arginine methyl ester (L-NAME; 20 mg/rat/day), BAY 41-2272 (20 mg/kg/day) and L-NAME + BAY 41-2272. • Rats were treated with L-NAME concomitantly with BAY 41-2272 for 4 weeks. • Concentration-response curves to acetylcholine (ACh) and sodium nitroprusside (SNP), along with the nitrergic relaxations (1-32 Hz) were obtained in rat corpus cavernosum (RaCC). • The RaCC contractile responses to the α₁ -adrenoceptor agonist phenylephrine (PE) were obtained.

RESULTS

• Acetylcholine (0.01-1000 µmol/L) produced concentration-dependent relaxing responses in RaCC that were significantly enhanced (P < 0.05) in BAY 41-2272-treated rats. • The ACh-induced relaxations were largely reduced in L-NAME-treated rats, and co-treatment with BAY 41-2272 failed to significantly modify these impaired relaxations. • The SNP-induced relaxations were modified neither by L-NAME nor by co-treatment with BAY 41-2272. • The nitrergic relaxations were significantly amplified in BAY 41-2272-treated rats (at 16 and 32 Hz). A significant reduction in the nitrergic relaxations was observed in L-NAME-treated rats, an effect largely restored by co-treatment with BAY 41-2272. • The contractile RaCC responses produced by PE (0.001-100 µmol/L) were significantly higher (P < 0.05) in L-NAME-treated rats, and co-treatment of L-NAME with BAY 41-2272 nearly restored these enhanced contractile responses.

CONCLUSION

• Four-week therapy with BAY 41-2272 prevents the impaired corpus cavernosum relaxations of rats treated chronically with L-NAME, indicating that accumulation of cyclic guanosine monophosphate into erectile tissue counteracts the NO deficiency.

Intracavernous Chlorpromazine Versus Phentolamine: A Double‐blind Clinical Comparative Study

INTRODUCTION

Intracavernous pharmacotherapy is one of the most common treatment modalities of erectile dysfunction (ED). There are different drugs that are used for intracavernous injection including papaverine, phentolamine, prostaglandins E1, phenoxybenzamine, and moxisylate.

AIM

The aim of this study is to evaluate the efficacy of chlorpromazine as an intracavernous vasoactive agent alone or with other drugs.

METHODS

This study was performed on 50 patients presenting to our department complaining of ED. Patients were divided into three groups according to the type of intracavernous drug injected. Group A included 20 patients who received an intracavernous injection of 1 mL bimix (30 mg papaverine + 1 mg phentolamine) followed a week later by intracavernous test dose using a 1 mL mixture of papaverine and chlorpromazine (30 mg papaverine + 2.5 mg chlorpromazine). Group B included 20 patients who received an intracavernous injection of 1 mL trimix (30 mg papaverine + 1 mg phentolamine + 10 microg PGE1). A week later they received another intracavernous test dose using a 1 mL mixture of papaverine, PGE1, and chlorpromazine (30 mg papaverine + 2.5 mg chlorpromazine + 10 microg PGE1). Group C included 10 patients who received various intracavernous injections of chlorpromazine in doses 1 mg, 2 mg, 5 mg, and 10 mg.

RESULTS

There was no significant difference in erection response and erection duration between phentolamine and chlorpromazine. Prolonged erection occurred in two patients of group B and postural hypotension occurred in three patients of group C.

CONCLUSION

Chlorpromazine can be used as an intracavernous vasoactive agent; it is similar to phentolamine in efficacy and short-term side effect profile.

Erectile dysfunction: expectations beyond phosphodiesterase type 5 inhibition

In the last few years the pathophysiological mechanisms of erection have been partially clarified, and the molecular machinery of the cellular components of the corpus cavernosum (CC) has been widely investigated. Since erection is a vascular event and the penis is a vascular organ, there must be an intact endothelium for an erection to occur. The regulation of penile tumescence inside the CC involves a balance between contracting and relaxing factors which regulate the functional state of smooth muscle cells. Recent studies have highlighted the importance of new local factors (i.e. phosphodiesterases, rho-kinases and endothelins), and pharmacological agents are available in the armamentarium of the specialist which are targeted to modulate the function of those mediators of erection. It is now well understood that male erectile dysfunction (ED) is a symptom rather than a disease; for this reason in the near future both general practitioners and specialists in internal medicine would have to interplay with sexual medicine. This review is intended to give the clinician some basic concepts of the pathophysiology of erection with relevance to the clinical practice, and to discuss the newest therapeutic approaches for those patients who do not respond to the treatment with oral inhibitors of phosphodiesterase Type 5.

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.

Pharmacology of erectile function and dysfunction

Central regulation of the erectile process involves several transmitters, including dopamine, serotonin, noradrenaline, and nitric oxide, and peptides, such as oxytocin and ACTH/alpha-MSH. These systems may be targets for future drugs designed to treat erectile dysfunction. Peripherally, the different steps involved in neurotransmission, impulse propagation, and intracellular transduction of neural signals in penile smooth muscles need further investigation. Continued studies of the interactions between different transmitters/modulators may reveal new combination therapies. Increased knowledge of the changes in penile tissues associated with erectile dysfunction may explain the pathogenetic mechanisms and help to prevent the disorder.

Non-surgical management of erectile dysfunction

Erectile dysfunction is a common and distressing medical condition that is now highly amenable to treatment almost irrespective of the cause. Safe, non-surgical treatments with unequivocal efficacy are psychological therapy, intracorporeal injection of vasoactive drugs, transurethral vasodilators and oral sildenafil, all of which have been reported to have a 50-70% overall response rate. Vacuum constriction devices are acceptable for some, usually older patients and oral yohimbine is thought to have marginal efficacy. Local creams to induce or enhance erectile function are currently being investigated. There is no place for androgen supplementation unless the patient is profoundly hypogonadal. Treatment of hyperprolactinaemia is very effective but is a rare cause of erectile dysfunction. As intercourse may entail an unfamiliar level of physical activity, it is sensible to ensure that the patient is able to climb a flight or two of stairs comfortably without provoking undue breathlessness or chest pain and to provide suitable advice about technique before commencing treatment. Once it is clear to the patients that erectile dysfunction can be satisfactorily overcome, the long-term use of treatments to do so tends to wane. Thus, although the prospect of effective treatment for what had been for many a distressing life sentence has the potential to place new demands on the health service, there is no evidence that restrictions on prescribing will prove economically rational.

Moxisylyte: a review of its pharmacodynamic and pharmacokinetic properties, and its therapeutic use in impotence

Moxisylyte is a competitive noradrenaline antagonist, acting preferentially on post-synaptic alpha-1 adrenoceptors. It was introduced more than thirty years ago for the treatment of cerebro-vascular disorders and shown more recently effective in the urological field due to its ability to modulate the urethral pressure. Renewal of interest in this drug has been observed in recent years since the demonstration of the possibilities of vasoactive drugs in evaluation and treatment of erectile dysfunctions. Moxisylyte is a prodrug, rapidly transformed into an active metabolite in plasma (Deacetylmoxisylyte or DAM). Elimination of the active metabolite occurs by N-demethylation, sulpho- and glucuroconjugation. The N-demethylated metabolite is sulphoconjugated only. Urine is the main route of excretion. The metabolites of moxisylyte can be determined in biological fluids by various methods using high-performance liquid chromatography. Their pharmacokinetics is dependent on the route of administration. By the oral route, the concentrations of the active metabolite are low, and the glucuroconide of DAM predominates over the sulphates. After intravenous and intracavernous injection, the active metabolite is proportionally higher, the two sulphates are equivalent and in larger amounts than the glucuronide. In the treatment of impotence, intracavernous injection of moxisylyte at 10, 20 or 30 mg can induce an erection adequate for intercourse in most of the patients. Compared to inducing agents such as papaverine and prostaglandin E1, moxisylyte must be considered as a facilitator of male erection, its interest lying in the low rate of adverse effects, either general or local.

Intracavernous pharmacotherapy

Intracavernous application of vasoactive substances not only has enhanced our understanding of penile hemodynamics, the physiology of penile erection, and the pathophysiology of erectile dysfunction but also has revolutionized the diagnosis and treatment of erectile dysfunction in the last 15 years. Virag was the first to report on the erectile effect of papaverine in humans, and Brindley later reported the effect of intracavernous application of alpha-receptor-blocking agents on cavernous tissue. These reports led to numerous basic and clinical investigations and ultimately established a new treatment alternative for patients with erectile dysfunction that is now considered to be the treatment of choice for most patients. Changes in penile hemodynamics include the relaxation of cavernous smooth musculature and arteries, which leads to an increase in arterial blood flow and a restriction of venous outflow through a compression of subtunical veins. These hemodynamic changes are the prerequisite for the induction and maintenance of penile erection. With the intracavernous application of vasoactive substances it was possible to influence penile hemodynamics at a local level and to induce an erection despite alterations in the nervous system, penile arterial blood flow, cavernous musculature, or neurotransmitter status. In addition, the local application of pharmacologically active substances directly to the end organ enabled the achievement of high local drug concentrations without severe systemic side effects. The commonly used substances are papaverine the combination of papaverine and phentolamine, and prostaglandin E1 (alprostadil). In addition to these established substances, several other regimens, such as linsidomine (SIN-1), calcitonin gene-related peptide (CGRP), moxisylyte, and various triple- or quadruple-drug mixtures have been described. In addition, several other compounds as well as different routes of administration are on the horizon and may prove to be effective in the future diagnosis and treatment of erectile dysfunction.

Adrenergic receptors on smooth muscle cells isolated from human penile corpus cavernosum

The effect of the alpha-adrenergic blocker moxisylyte was examined on smooth muscle cells isolated from human corpus cavernosum, and compared with that of other adrenergic agents and papaverine. Isolated smooth muscle cells were shown to contract (reduction of the mean cell length) under noradrenaline and carbachol stimulations in a time-dependent and concentration-dependent manner (maximum at 30 seconds, EC50 [noradrenaline] = 5 nM., EC50 [carbachol] = 1 nM.). The contractile effect of noradrenaline was dose-dependently inhibited by moxisylyte (IC50 = 0.5 +/- 0.2 microM.) and by prazosin (IC50 = 0.9 +/- 0.2 microM.). The dose-response curves were parallel and no statistically significant difference could be shown between the IC50 values. The alpha 2-adrenergic antagonist tolazoline also inhibited noradrenaline-induced contraction, whereas the alpha-adrenergic agonist methoxamine did not change the mean cell length. As expected, isoproterenol caused relaxation of noradrenaline-precontracted cells by interaction with a beta 2-adrenergic receptor. Papaverine was also found to inhibit the contraction induced by noradrenaline in a dose-dependent manner (IC50 = 2 +/- 0.3 nM.). Tritiated-dihydroergocryptine (3H-DHE) specific binding was competitively inhibited by moxisylyte and prazosin with the same IC50 value of 0.01 microM. Methoxamine and tolazoline also inhibited this binding with lower affinity (IC50 = 0.1 +/- 0.02 microM.), while isoproterenol did not change specific binding. Scatchard plots from saturation experiments with 3H-DHE and with 3H-N-methyl scopolamine revealed the presence of 15 times more adrenergic than muscarinic binding sites (650,000 and 45,000 sites per cell, respectively). Together, these data support evidence for the presence of postsynaptic alpha 1-adrenergic receptors on smooth muscle cells from human corpus cavernosum. These receptors are coupled with the contraction of the cell and are blocked by the alpha 1-adrenergic antagonists moxisylyte or prazosin. They also show that the phosphodiesterase inhibitor papaverine and the beta-adrenergic agonist isoproterenol induced relaxation. This model constitutes a new approach to study the potential targets of the adrenergic agents in the erectile tissue.

Efficiency and side effects of intracavernous injections of moxisylyte in impotent patients: a dose-finding study versus placebo

We assessed the efficiency and tolerance of the alpha-blocking agent moxisylyte in 2 double-blind studies versus placebo performed in 12 neurogenic patients with spinal cord lesions and in 61 patients presenting with either psychogenic impotence (30) or erectile dysfunction that was predominantly neither psychogenic, hormonal nor neurogenic (31). In each etiological group patients were randomized (according to latin square method) to receive 3 single doses (10, 20 and 30 mg.) of moxisylyte and a placebo. The erectile response was determined 5, 10, 15, 20 and 30 minutes after each injection. Whatever etiology of impotence and dosage tested, the erectile response induced by moxisylyte was significantly higher than the placebo-induced response. No difference occurred among the 3 doses. In 93% of the patients moxisylyte induced an erectile response, including tumescence in 6, partial rigidity in 16 and complete rigidity in 46. Thus, in 62 of 73 patients (85%) the drug allowed initiation of erection adequate for intercourse. Placebo induced such erection in only 25% of the cases and in 55% there was no response. Tolerance was good and no priapism occurred. Only 4 patients (5%) reported mild pain during injection but erections were never painful, 1 presented with moderate and transient hypotension at the 20 mg. dose and a painless prolonged erection was observed in 1 case after the lowest dose. Drugs such as moxisylyte should be given before less well tolerated drugs.

Moxisylyte plasma kinetics in humans after intracavernous administration

Obtaining and sustaining an erection are common problems for the male spinal cord injury patient. Intracavernous injection of vasoactive substances offers a new treatment option but it must be approached with caution in this population. In this work, the use of an alpha-adrenergic blocking agent, moxisylyte, after intracavernous administration for complete paraplegic patients with erectile impotence is described. During this study, the pharmacokinetic profile of moxisylyte has been defined. Unchanged moxisylyte is not found in plasma, this drug is immediately metabolized after administration. Three metabolites were found in plasma: desacetylmoxisylyte (DAM), conjugated DAM, and conjugates of desmethylated DAM (MDAM). Maximum plasma levels of 72.3 ng ml-1, 301.4 ng ml-1, and 88.8 ng ml-1 are obtained 0.22 h, 0.9 h, and 2.08 h after drug administration for these three metabolites, respectively. The elimination half-lives are 0.89 h, 2.16 h, and 5.32 h and the MRT, 1.38 h, 3.23 h, and 8.45 h, respectively. No side-effects were noted, only one patient presented sleepiness. Successful erections (10 to 25 min) were obtained in all patients and no priapism was noted.