Evolution of phosphodiesterase type 5 inhibitors in treatment of erectile dysfunction in Taiwan

Erectile dysfunction (ED) is a prevalent form of male sexual dysfunction. Phosphodiesterase type 5 (PDE5) inhibitor is the first-line treatment for ED. Numerous well-designed and -conducted clinical trials and postmarketing studies have established the safety and efficacy of PDE5 inhibitors for the treatment of ED. Ever since the first approval of sildenafil in 1998, PDE5 inhibitors have had several advances in their clinical use. More new agents with different pharmacokinetic profiles and new formulations were marketed. Conventional on-demand administration expanded to daily dosing. These advances provide more flexibility in clinical treatment of ED for patients and physicians. Moreover, clinical indications of PDE5 inhibitors extend from treatment of ED to pulmonary arterial hypertension and signs and symptoms of benign prostatic hyperplasia because of the distribution of PDE5 enzyme in human organs and tissues. The evolution of PDE5 inhibitors heralds a remarkable medical history from bench to clinical practice.     

Non-responders to phosphodiesterase type 5 inhibitors: is there a second chance?

Phosphodiesterase type 5 (PDE5) inhibitors are, today, the first treatment option for erectile dysfunction (ED). However, efficacy does not exceed 70%, while the drop-out rate is high. Therefore, salvage strategies and second/third line treatment options are necessary to restore erectile response in such patients. This literature review of the currently available data on non-responders to PDE5 inhibitors aims to discuss key issues that physicians address in everyday clinical practice. These issues include the definition of treatment failure, the identification of factors that affect treatment outcome and the management strategy for non-responders to PDE5 inhibitors. Medication, clinical and patient/partner related issues have been identified as factors related to treatment failure. Treatment outcome assessment is based not only on quality of erectile response, but also on side effect profiles and patient satisfaction. Proper instructions for PDE5 inhibitor administration and psychosexual counselling may convert a substantial number of non-responders to responders. Inappropriate use of PDE5 inhibitors is a major issue in clinical practice. Non-responders may be converted to responders after careful assessment of the proper use of a PDE5 inhibitor. Treatment options for true non-responders are under investigation and include chronic administration of PDE5 inhibitors (everyday, low dose use), switchover from one drug to another or combination treatments. Management strategies must identify patient and partner needs and expectations and involve them in the decision-making.     

Erektile Dysfunktion

Erectile dysfunction (ED) tends to be associated with other diseases, the common basis of which is endothelial dysfunction. ED is also frequently combined with LUTS and the common basis for both conditions seems to be elevation of Rho-kinase activity and decrease of NO concentration. Because all three PDE 5 inhibitors sildenafil, tadalafil, and vardenafil have a common mode of action, i.e., inhibition of PDE 5, they are not different in terms of their efficacy and safety profile except for color vision disturbances which are more common after sildenafil and back pain/myalgia more often observed after tadalafil. The main differentiating characteristics among the three PDE 5 inhibitors are their pharmacokinetics. These are ultimately responsible for the observation that in head-to-head comparative trials depending on the respective study design the overwhelming majority of the patients opted either for tadalafil as the longest acting PDE 5 inhibitor (36 h) or for vardenafil as a relatively rapidly acting drug.All published studies so far have shown that in terms of the cardiovascular risk profile (myocardial infarction rate) all three PDE 5 inhibitors performed better than placebo although the results were not statistically significant. Without any exception it applies to all three PDE 5 inhibitors that they are absolutely contraindicated in patients taking nitrate- or molsidomine-containing medications and that they may interact in particular with non-uroselective alpha-adrenoceptor blockers. This is why their simultaneous application with PDE 5 inhibitors has to be avoided.In the near future chronic (daily) application of a PDE 5 inhibitor may show advantages, at least in those 50-60% of all patients in whom there is a high likelihood of endothelial dysfunction due to the diagnostic (penile duplex Doppler) outcome. Possible new developments in the management of ED with a time frame of 5-8 years until their market approval are guanylate cyclase activators, Rho-kinase inhibitors, melanocortin receptor agonists, gene therapy, and tissue engineering.     

Newer phosphodiesterase inhibitors: comparison with established agents

Erectile dysfunction is defined as the consistent or recurrent inability to attain or maintain penile erection sufficient for sexual performance. Self-reported erectile dysfunction has increased significantly as men seek effective therapy, such as oral phosphodiesterase 5 inhibitors (PDE5i). PDE5i are now the drugs of choice in the initial therapy of erectile dysfunction. This review compares the currently available PDE5i with the second-generation PDE5i, which are soon to be available.     

Drug Insight: oral phosphodiesterase type 5 inhibitors for erectile dysfunction

Erectile dysfunction (ED) is a common medical condition that affects the sexual life of millions of men. At present, first-line oral pharmacotherapy for most patients with ED is a phosphodiesterase type 5 (PDE-5) inhibitor, of which three are currently available worldwide. Sildenafil (Viagra, Pfizer) has a very satisfactory efficacy-safety profile in all patient categories. The first PDE-5 inhibitor to reach the market, it is now the most widely prescribed oral agent for ED. Tadalafil (Cialis, Lilly ICOS) and vardenafil (Levitra, Bayer/GlaxoSmithKline) were introduced to the European Union and the US in 2003 and 2004, respectively. These three PDE-5 inhibitors share many characteristics, but each has unique features. This review describes the chemical, pharmacologic and clinical features of sildenafil, vardenafil and tadalafil as oral first-line treatments for ED. First, we describe the physiology of penile erection and PDE-5 inhibitor pharmacology, including chemistry, PDE selectivity, pharmacokinetics, and possible drug interactions. We then summarize data on the efficacy and safety profiles of the three PDE-5 inhibitors for the treatment of ED in the general population, in patients with diabetes mellitus and in men that have undergone bilateral nerve-sparing retropubic radical prostatectomy.     

Chronic low dosing of phosphodiesterase type 5 inhibitor for erectile dysfunction

Oral phosphodiesterase type 5 (PDE5) inhibitors have provided non-invasive, effective, and well-tolerated treatments for patients with erectile dysfunction (ED). However, many patients with ED are unresponsive to 'on-demand' PDE5 inhibitors. In addition, the lack of spontaneity and naturalness of the on-demand regimen could be a reason for decreased compliance with PDE5 inhibitors. Recently, tadalafil and udenafil were approved for low-dose daily administration for the treatment of ED. Since the introduction of the concept of daily administration of PDE5 inhibitors, several reports have supported the potential benefits of this therapy for disease modification, improvement of the treatment response in difficult-to-treat populations, spontaneity, and safety, although further research is needed to better address these hypotheses. In this article, we reviewed the daily administration of PDE5 inhibitors in terms of pharmacokinetics, safety, efficacy, and distinct features.     

Tissue expression, distribution, and regulation of PDE5

Phosphodiesterase 5 (PDE5) has been identified in many species. The three isoforms, PDE5A1, PDE5A2, and PDE5A3, differ only in their N-terminal sequence. PDE5A1 and PDE5A2 are ubiquitous, but PDE5A3 is specific to smooth muscle. The initial three exons (A1-A3-A2) of PDE5A, located on chromosome 4q26, are alternative first exons encoding the isoform-specific sequences. The PDE5A promoter overlaps with the A1-specific exon, while the PDE5A2 promoter is located between the A3- and A2-specific exons. Both respond to cyclic guanosine monophosphate (cGMP) or cyclic adenosine monophosphate (cAMP) stimulation. The PDE5A2 promoter contains an Sp1-binding sequence critical for basal and cGMP/cAMP-inducible promoter activities. PDE5A is induced by adjacent sequences (enhancers) containing Sp1-binding sites. The potential role of PDE5A promoters in the tachyphylaxis effect of PDE5 inhibitors is currently being investigated. Preliminary data suggest that hypoxia might down-regulate PDE5A promoters, implying an involvement of PDE5 in stuttering priapism.     

Effects of phosphodiesterase-5 inhibitors on sperm parameters and fertilizing capacity

The aim of this review study is to elucidate the effects that phosphodiesterase 5 （PDE5） inhibitors exert on spermatozoa motility, capacitation process and on their ability to fertilize the oocyte. Second messenger systems such as the cAMP/adenylate cyclase （AC） system and the cGMP/guanylate cyclase （GC） system appear to regulate sperm functions. Increased levels of intracytosolic cAMP result in an enhancement of sperm motility and viability. The stimulation of GC by low doses of nitric oxide （NO） leads to an improvement or maintenance of sperm motility, whereas higher concentrations have an adverse effect on sperm parameters. Several in vivo and in vitro studies have been carried out in order to examine whether PDE5 inhibitors affect positively or negatively sperm parameters and sperm fertilizing capacity. The results of these studies are controversial. Some of these studies demonstrate no significant effects of PDE5 inhibitors on the motility, viability, and morphology of spermatozoa collected from men that have been treated with PDE5 inhibitors. On the other hand, several studies demonstrate a positive effect of PDE5 inhibitors on sperm motility both in vivo and in vitro. In vitro studies of sildenafil citrate demonstrate a stimulatory effect on sperm motility with an increase in intracellular cAMP suggesting an inhibitory action of sildenafil citrate on a PDE isoform other than the PDE5. On the other hand, tadalafil＇s actions appear to be associated with the inhibitory effect of this compound on PDE11. In vivo studies in men treated with vardenafil in a daily basis demonstrated a significantly larger total number of spermatozoa per ejaculate, quantitative sperm motility, and qualitative sperm motility; it has been suggested that vardenafil administration enhances the secretory function of the prostate and subsequently increases the qualitative and quantitative motility of spermatozoa. The effect that PDE5 inhibitors exert on sperm parameters may lead to the improvement of the outcome of assi     

Vardenafil preclinical trial data: potency, pharmacodynamics, pharmacokinetics, and adverse events

Vardenafil potently inhibits human phosphodiesterase 5 (PDE5) with an IC50 of 0.7 nM. Enhancement of nitric oxide (NO)-induced erections in rabbits by 0.1 mg/kg vardenafil is limited by its pharmacokinetic properties (Tmax=1 h; T1/2=1.2 h), although erectile effects have been observed after 7 h. In humans, vardenafil is rapidly absorbed (Tmax approximately 40 min) and more slowly metabolized (T1/2 approximately 4 h), with an absolute bioavailability of 14.5% (vs 40% for sildenafil). Although the consumption of high-fat meals does not affect the drug's relative bioavailability, it retards intestinal absorption. Coadministration of CYP3A4 inhibitors such as ritonavir can affect hepatic metabolism. M1, an active metabolite of vardenafil, is a four-fold-less potent inhibitor of PDE5 than its parent compound, contributing approximately 7% to vardenafil's overall efficacy. The side effects of all selective PDE5 inhibitors commonly include vasodilation, small reductions in blood pressure, headache, and nasal congestion.     

Treating erectile dysfunction by endothelial rehabilitation with phosphodiesterase 5 inhibitors

A large body of evidence has accumulated demonstrating that a common pathway in conditions such as hypertension, atherosclerosis, hypercholesterolemia, diabetes mellitus, and erectile dysfunction (ED) is endothelial dysfunction. Although a complete pharmacological cure for ED is currently unavailable, the phosphodiesterase 5 (PDE5) inhibitors sildenafil, vardenafil, and tadalafil are efficacious oral therapy for ED. Results from recent studies suggest that regular treatment with a PDE5 inhibitor may lead to enhanced erectile function (EF) beyond that observed with on-demand usage, possibly through improvement of endothelial function. Such an effect may be viewed as rehabilitation of damaged erectile tissue. The present review focuses on several recent studies which provide evidence for the beneficial effect of regular PDE5 inhibitor administration on the improvement of EF by rehabilitation of vascular endothelium.     

Phosphodiesterase type 5 inhibitors: state of the therapeutic class

With three effective and safe phosphodiesterase type 5 (PDE5) inhibitors, the clinician now has multiple choices in the treatment of patients who have erectile dysfunction of all severities and etiologies. Based on pharmacokinetics, pharmacodynamics, efficacy, and safety, each of these agents can be used. Because no well-controlled head-to-head selection or patient preference studies are available, each clinician must choose an agent based on the profile of the patient, his tolerance, risk factors, and side effects. This discussion summarizes some of the current data on PDE5 inhibitors and their efficacy, safety, and use in other conditions.     

JNJ-10280205 and JNJ-10287069: Novel PDE5 inhibitors as clinical candidates for erectile dysfunction

Phosphodiesterase 5 (PDE5) inhibitors are efficacious in treating patients with erectile dysfunction. New PDE5 inhibitors with different selectivity and pharmacokinetic profiles have been vigorously pursued. Here we report two novel, potent, and selective PDE5 inhibitors, JNJ-10280205 and JNJ-10287069, with Ki values of 0.05 and 0.12 nM, respectively. Both compounds displayed superior selectivity against PDE1-4 and -6 when compared to sildenafil. In the anesthetized dogs, JNJ-10280205 and JNJ-10287069 exhibited similar efficacy as sildenafil in enhancing erectile functions, with no significant effect on cardiovascular parameters. Pharmacokinetic studies showed that JNJ-10287069 had better oral bioavailability than JNJ-10280205 in several animal species. In vitro study suggested that cytochrome P450 (CYP) 3A4 played a major role in the metabolism of both compounds. The compounds inhibited some of the CYP450 enzymes and the human ether-a-go-go (HERG) channel at much higher concentrations than that required to inhibit PDE5, thus, no cross inhibition would be expected at therapeutic doses. Both compounds are suitable clinical candidates.     

Diabetic nephropathy: Treatment with phosphodiesterase type 5 inhibitors

The importance of nitric oxide (NO) in vascular physiology is irrefutable; it stimulates the intracellular production of cyclic guanosine monophosphate (cGMP), initiating vascular smooth muscle relaxation. This biochemical process increases the diameter of small arteries, regulating blood flow distribution between arterioles and the microvasculature. The kidney is no exception, since NO predominantly dilates the glomerular afferent arterioles. It is now evident that the vascular production of cGMP can be augmented by inhibitors of phosphodiesterase type 5 (PDE 5), the enzyme which breakdowns this cyclic nucleotide. This has clinical relevance, since diabetic nephropathy (DN) a major microvascular complication of diabetes mellitus and the most common cause of end-stage renal disease, increases intraglomerular capillary pressure, leading to glomerular hypertension. PDE 5 inhibitors may have, therefore, the potential to reduce glomerular hypertension. This review describes the use of PDE 5 inhibitors to improve the metabolic, haemodynamic and inflammatory pathways/responses, all of which are dysfunctional in DN.     

PDE5抑制剂治疗缺血再灌注损伤研究进展

5型磷酸二酯酶(PDE5)抑制剂常用于治疗男性阴茎勃起功能障碍。近年来,有实验研究表明PDE5抑制剂可用于治疗器官组织缺血再灌注损伤,本文就PDE5抑制剂治疗缺血再灌注损伤的基础和临床研究成果作一综述,以期为临床医生选择使用PDE5抑制剂提供理论依据。     

勃起功能障碍（ED）的联合疗法

二十世纪九十年代末二十一世纪初,口服PDE5抑制剂（PDE5Is）的引入在很大程度上革新了性医学领域。目前PDE5I已经成为勃起功能障碍（ED）的首选单一疗法。然而,对一些复杂型ED患者来说,PDE5I单一疗法的疗效还不尽人意。目前越来越多不易治疗的ED病例开始采用联合疗法治疗,但还缺少对当前使用的联合疗法的严格评估。基于此,本综述在Pubmed和Cochrane Library数据库中进行了全面的文献检索．主要检索对象是1990年1月到2010年12月间研究PDE5I单一治疗失败后接受联合疗法的所有相关综述、随机对照试验、队列研究和回顾性研究。同时还对检索所得文献的参考文献进行了人工筛选,获得了其它一些相关的文献资料。目前发表的联合疗法主要包括PDE5I加真空吸引器（VED）、尿道给药、阴茎注射（ICI）、雄激素补充疗法、α-阻断剂,还有其它一些联合疗法。本综述发现,有些联合疗法的初步试验结果是有效的。然而,进行治疗时还是要谨慎,因为近十年来发表的大部分联合疗法相关文章的研究方法有很多问题,比如研究偏见和样本量小等。尽管如此,目前的研究结果还是在为将来复杂型ED的治疗研究方面奠定了坚实的基础。     

PDE5 inhibitors beyond erectile dysfunction

The phosphodiesterase type-5 (PDE5) inhibitors sildenafil, vardenafil and tadalafil are widely used first-line therapy for erectile dysfunction (ED). Since the advent of sildenafil in 1998, more than 40 million men worldwide have been successfully treated with these compounds. The safety and high tolerability of PDE5 inhibitors make them an attractive tool to investigate further physiological functions of PDE5, for example the modulation of intracellular cyclic GMP (cGMP) pools. As cGMP is a key component of intracellular signaling this may provide novel therapeutic opportunities beyond ED even for indications in which chronic administration is necessary. The approval of sildenafil for the treatment of pulmonary hypertension in 2005 was a notable success in this area of research. A number of other potential new indications are currently in various phases of preclinical research and development. In recent years, extensive but very heterogeneous information has been published in this field. The aim of this review is to summarize existing preclinical and clinical knowledge and critically discuss the evidence to support potential future indications for PDE5 inhibitors.     

Rationale for phosphodiesterase 5 inhibitor use post-radical prostatectomy: experimental and clinical review

Erectile dysfunction (ED) is a common complication after radical prostatectomy and results from trauma sustained by the cavernosal nerves. This is a major concern for patients and often affects treatment decisions. The likely mechanism for post-prostatectomy ED is through corporal veno-occlusive dysfunction. There is an increasing amount of evidence to suggest that phosphodiesterase 5 inhibitors (PDE5 inhibitors), when given on a continuous long-term basis, can help to prevent and reverse ED after surgery. In this review article we will examine the pathophysiology of post-prostatectomy ED and discuss the experimental and available clinical evidence for administering PDE5 inhibitors after prostatectomy.     

A Novel Treatment of Premature Ejaculation

The investigation of the etiology and treatment of premature ejaculation (PE), a common and significant problem for men and their partners, has been limited by the lack of defined outcomes and differences in clinical trial designs. Currently, no medication has been approved for the treatment for PE worldwide. Recognition of serotonin as a key mediator in ejaculatory signaling has raised interest in the utility of pharmacologic intervention for treating PE. Selective serotonin reuptake inhibitors (SSRIs) have been used off-label for PE, with varied results. However, treatment with currently available SSRIs typically requires chronic dosing that increases drug accumulation and the attendant risk of adverse events. Dapoxetine is an SSRI with a short half-life (1.2 h), developed specifically for the treatment of men with PE. This agent has a unique pharmacokinetic profile characterized by rapid absorption and elimination. Dapoxetine is metabolized by multiple pathways, and no clinically relevant drug–drug interactions have been identified. Furthermore, dapoxetine pharmacokinetics do not appear to be affected by food, age, alcohol, or phosphodiesterase type 5 (PDE5) inhibitors to a relevant degree. In two placebo-controlled phase 3 trials involving >2600 men with PE, dapoxetine 60 mg given as needed over 12 wk significantly prolonged the stopwatch-assessed intravaginal ejaculatory latency time (IELT) from 0.91 min at baseline to 3.32 min (p < 0.0001), increased control over ejaculation, and increased sexual satisfaction for men and their partners compared with placebo (both p < 0.0001). These results suggest that dapoxetine may meet the medical need for on-demand therapy for PE.