同期内使用3种PDE5抑制剂治疗ED的经验

目的:观察与比较同期内使用3种PDE5抑制剂治疗ED患者的疗效,满意情况和不良反应。分析影响患者疗效、接受度、倾向性的因素。方法:11个月在门诊应用3种PDE5抑制剂治疗ED患者331例。使用西地那非134例,他达拉非88例,及伐地那非109例。医师详细指导药物的应用,注意事项,观察的内容等,并互留电话,列表登记、随访。结果:复诊或电话随访时间,结果为:①获得良好的疗效及满意率为西地那非72例(79.12%),他达拉非52例(78.78%),伐地那非63例(81.81%)。②PDE5抑制剂单纯或交叉应用的资料分析显示:青年患者或新婚者,偏好伐地那非;③中青年患者倾向于他达拉非;中老年及较长期应用PDE5抑制剂的患者多选用西地那非。3种PDE5抑制剂用于早泄均有一定疗效。④对不能继续用此类药治疗ED的原因进行了分析,分别为:价高,不治本,效果差,耽心不良反应。结论:①同期3种PDE5抑制剂治疗ED的疗效基本相近。亦各有一些优势和特点。②3种PDE5抑制剂的安全性均好,一般、轻度不良反应相近,中度、特殊的不良反应少,严重不良反应均无发生。③PDE5抑制剂的疗效观察,目前众多的问卷、量表实际均仍以主观的感受为主。对同一个人以相同形式、相同问题、繁简一致阐述,获得的有关疗效满意情况、感受等简易回答是有可比性、可信度和实用性的。     

Efficacy and safety of long‐term tadalafil 5 mg once daily combined with sildenafil 50 mg as needed at the early stage of treatment for patients with erectile dysfunction

This study aimed to evaluate the efficacy and safety of long‐term and low‐dose tadalafil combined with sildenafil as needed at the early stage of treatment for erectile dysfunction (ED). We enrolled 180 patients with ED 1 : 1 to tadalafil 5 mg once daily or once‐a‐day tadalafil 5 mg combined with sildenafil 50 mg as needed. The efficacy measures included the 5‐item version of the International Index of Erectile Function (IIEF‐5) and the Sexual Encounter Profile (SEP). The safety was assessed by observing drug tolerability and adverse events. Total IIEF‐5 scores of patients with severe ED in combined medication group were significantly higher than in tadalafil alone group. Question 2 scores of IIEF‐5 of patients with moderate and severe ED in combined medication group were significantly higher than in tadalafil alone group. The significant improvement in question 3 scores of IIEF‐5 existed only in patients with severe ED receiving combined medication. The percentage of ‘yes’ responses to SEP4, SEP5 and partner's SEP3 were improved significantly in combined medication group. There was no difference between two groups in the incidence of adverse events. Our results suggest that combined medication can better improve erectile function, especially for patients with severe ED.     

Erectile dysfunction secondary to nerve-sparing radical retropubic prostatectomy: Comparative phosphodiesterase-5 inhibitor efficacy for therapy and novel prevention strategies

Postprostatectomy erectile dysfunction appears to be initiated by neuropraxia and perpetuated by cavernosal smooth muscle apoptosis. Phosphodiesterase-5 (PDE-5) inhibitor therapy is the current cornerstone of erectile dysfunction (ED) therapy in this population. Although no head-to-head trials have been performed with sildenafil, vardenafil, and tadalafil in this population, there are numerous studies in the general ED population. The results of these studies demonstrate that neither of the new PDE-5 inhibitors met statistical noninferiority to sildenafil. Sildenafil has been studied in a novel primary prevention modality using nightly administration after a bilateral nerve-sparing prostatectomy. In this novel approach, it effected a sevenfold improvement in return of spontaneous, normal erectile function 2 months after drug discontinuation. This effect appears to be mediated by properties unique to sildenafil that include improved endothelial function and neuronal regeneration and neuroprotection. In primary prevention, unlike ED therapy, one has only “one shot” by definition. Therefore, it is even more critical to apply evidence-based medicine.     

Pre-clinical evidence for the use of phosphodiesterase-5 inhibitors for treating benign prostatic hyperplasia and lower urinary tract symptoms

OBJECTIVE: To evaluate the potential of sildenafil, vardenafil and tadalafil, all phosphodiesterase-5 (PDE-5) inhibitors used for treating erectile dysfunction, for treating benign prostatic hyperplasia (BPH) and lower urinary tract symptoms (LUTS). MATERIALS AND METHODS: The mRNA expression of the PDE-5 was determined in rat LUT tissues. The PDE-5 inhibitors were also tested in organ-bath experiments and in a partial bladder outlet obstruction (BOO) rat model in vivo. RESULTS: The highest PDE-5 mRNA expression was in the bladder, followed by the urethra and prostate. PDE-5 inhibitors dose-dependently reduced the contraction of the isolated bladder, urethral and prostate strips. The rank order of potency was vardenafil > sildenafil > tadalafil. In human prostate stromal cells vardenafil inhibited cell proliferation and was more effective than tadalafil and sildenafil. In the BOO model, there was a reduction in the non-voiding contractions after bolus intravenous administration of 3 mg/kg sildenafil and vardenafil. CONCLUSION: These results show that PDE-5 is expressed in LUT tissues. PDE-5 inhibitors induced significant relaxation of these tissues, inhibited the proliferation of human prostate stromal cells and reduced the irritative symptoms of BPH/LUTS in vivo. Therefore, PDE-5 inhibitors could be used as an effective treatment for BPH/LUTS.     

Prevalence and medical management of erectile dysfunction in Asia

Erectile dysfunction (ED) is an important worldwide health issue that has a significant negative impact on the quality of life and life satisfaction of both the affected individual and his partner. Here we review the prevalence of ED in Asia, associated factors that may influence sexual attitudes and sexual behaviours, and randomized clinical trials (RCTs) of phosphodiesterase-5 (PDE-5) inhibitors to evaluate the clinical efficacy and safety of PDE-5 inhibitors in Asian men. We searched for English-language articles in MEDLINE and PubMed from January 2000 to September 2010. Our results showed that the overall reported prevalence rate of ED in Asia ranged widely, from 2% to 88%. This finding indicates that ED is a common and major health problem in this region. However, sociocultural and economic factors in Asia prevent people from seeking and obtaining appropriate medical care. We found reports on five kinds of PDE-5 inhibitors for the management of ED: sildenafil, vardenafil, tadalafil, udenafil and mirodenafil. The results of RCTs showed that these five PDE-5 inhibitors are more effective than placebo in improving erectile function in Asian men with ED and that these drugs have similar efficacy and safety profiles.     

Phosphodiesterase type 5 inhibitors for the treatment of erectile dysfunction in patients with diabetes mellitus

Sildenafil, a phosphodiesterase 5 (PDE5) inhibitor, has become a first-line therapy for diabetic patients with erectile dysfunction (ED). The efficacy in this subgroup, based on the Global Efficacy Question, is 56% vs 84% in a selected group of non-diabetic men with ED. Two novel PDE5 inhibitors, tadalafil (Lilly ICOS) and vardenafil (Bayer), have recently completed efficacy and safety clinical trials in 'general' and diabetic study populations and are now candidates for US FDA approval. A summary analysis of the phase three clinical trials of sildenafil, tadalafil and vardenafil in both study populations is presented to provide a foundation on which the evaluation of the role of the individual PDE5 inhibitors for the treatment of patients with ED and DM can be built.     

Therapeutic effectiveness and patient satisfaction after 6 months of treatment with tadalafil, sildenafil, and vardenafil: results from the erectile dysfunction observational study (EDOS)

OBJECTIVE: This observational study was conducted across Europe to assess health outcomes in men with erectile dysfunction (ED) who took tadalafil, sildenafil citrate (sildenafil), or vardenafil HCl (vardenafil) for 6 mo. METHODS: Therapy effectiveness and patient satisfaction were evaluated using established and new questions on erectile function. Behavioural, psychological, and relationship outcomes were assessed using the short form of the Psychological and Interpersonal Relationship Scales (SF-PAIRS). RESULTS: In nine European countries at 904 sites, 8047 patients were enrolled and 94% (7560) selected either tadalafil (5315), sildenafil (1252), or vardenafil (993) for treatment at baseline. Of the 7560, 3998 (52.9%) took the same drug for 6 mo. Baseline characteristics across the three treatment groups were comparable: mean age approximately 56 yr, moderate or severe ED, and mean International Index of Erectile Function-Erectile Function domain score about 13. Tadalafil, sildenafil, and vardenafil were therapeutically effective and improved patient satisfaction in the 40-58% of men who completed 6 mo of a single therapy. Patients taking tadalafil consistently had numerically higher levels of therapeutic effectiveness and satisfaction compared with patients who took sildenafil or vardenafil. The three cohorts had statistically significant changes from baseline in response to SF-PAIRS and there were significant differences, in favour of tadalafil, among cohorts in the Time Concerns domain. CONCLUSION: In a large observational study that mimics a routine clinical setting, most patients selected an inhibitor of phosphodiesterase 5 to treat ED, which resulted in a high level of therapeutic effectiveness and patient satisfaction.     

Clinical update on phosphodiesterase type-5 inhibitors for erectile dysfunction

Erectile dysfunction (ED) affects the sexual lives of millions of men. The first-line oral pharmacotherapy for most ED patients is phosphodiesterase type-5 (PDE-5) inhibitors, of which three are available. Sildenafil is the most widely prescribed oral agent for ED and has a very satisfactory efficacy–safety profile in all patient categories. Tadalafil and vardenafil were introduced in the European Union and in the United States in 2003 and 2004, respectively. The three PDE-5 inhibitors share many pharmacological and clinical characteristics, and each has unique features. This review, which is based on the contemporary literature on PDE-5 inhibitors, describes the chemical, pharmacological, and clinical features of sildenafil, vardenafil, and tadalafil. The first section reviews the pathophysiology of penile erection and PDE-5 inhibitor pharmacology. The second section summarizes data regarding efficacy and safety of the three drugs in treating ED in the general population as well as in selected patient categories.     

磷酸二酯酶5抑制剂治疗勃起功能障碍的疗效和安全性比较

磷酸二酯酶 5 (PDE 5 )抑制剂西地那非的问世使男性勃起功能障碍 (ED)的治疗手段发生了根本性的改变。1998年以来有 10 0多个国家的 2 0 0 0多万患者使用了西地那非 ,患者的死亡率与总体人群的死亡率差异无显著性。西地那非治疗ED平均有效率达 80 %以上 ,成为治疗ED的首选手段。随着新的PDE 5抑制剂伐地那非和泰地那非在国外先后进入临床使用 ,药物治疗ED有了更多的选择。本文通过比较 3种PDE 5抑制剂的药效学、药动学及不良反应以评价其疗效和安全性。     

The effects of chronic phosphodiesterase-5 inhibitor use on different organ systems

Phosphodiesterase-5 (PDE-5) inhibitors selectively inhibit PDE-5 enzymes that are present in various tissues like penile tissue, platelets, vascular, and smooth muscle tissue. The drug's actions on these tissues have lead to the successful therapeutic use in patients suffering from conditions such as erectile dysfunction (ED) and pulmonary hypertension. PDE-5 inhibitors (PDE-5i) act on the erectile tissue causing penile smooth muscle relaxation and vasodilatation leading to penile erection. In addition, in particular when used in conjunction with prostaglandin inhibitors, PDE-5i cause vasodilatation in pulmonary vasculature hence decreasing both the pulmonary arterial pressure and resistance. PDE-5i have also shown to mildly decrease blood pressure, increase cardiac index, and increase coronary blood flow in experimental animals as well as in human studies. The Food and Drug Administration (FDA) has approved three PDE-5i for the treatment of ED: sildenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis) and one for pulmonary hypertension: sildenafil (Revatio). These agents are highly selective for PDE-5 enzymes as compared to other subclasses of PDE enzymes and have the almost identical pharmacological action but slightly different pharmacokinetics. Only little data exist about long-term use of PDE-5i and their effects on different organ system. This paper reviews the current information available on chronic PDE-5 inhibitor use.     

Indirect comparison of interventions using published randomised trials: systematic review of PDE-5 inhibitors for erectile dysfunction

Background

There are no randomised and properly blinded trials directly comparing one PDE-5 inhibitor with another in a normal home setting. Valid indirect comparisons with a common comparator must examine equivalent doses, similar duration, similar populations, with the same outcomes reported in the same way.

Methods

Published randomised, double-blind trials of oral PDE-5 inhibitors for erectile dysfunction were sought from reference lists in previous reviews and electronic searching. Analyses of efficacy and harm were carried out for each treatment, and results compared where there was a common comparator and consistency of outcome reporting, using equivalent doses.

Results

Analysis was limited by differential reporting of outcomes. Sildenafil trials were clinically and geographically more diverse. Tadalafil and vardenafil trials tended to use enriched enrolment. Using all trials, the three interventions were similar for consistently reported efficacy outcomes. Rates of successful intercourse for sildenafil, tadalafil and vardenafil were 65%, 62%, and 59%, with placebo rates of 23–28%. The rates of improved erections were 76%, 75% and 71%, respectively, with placebo rates of 22–24%, and NNTs of 1.9 or 2.0. Reporting of withdrawals was less consistent, but all-cause withdrawals for sildenafil, tadalafil and vardenafil were 8% 13% and 20%. All three drugs were well tolerated, with headache being the most commonly reported event at 13–17%. There were few serious adverse events.

Conclusion

There were differences between trials in outcomes reported, limiting comparisons, and the most useful outcomes were not reported. For common outcomes there was similar efficacy between PDE-5 inhibitors.     

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.     

Efficacy and satisfaction rates of oral PDE5is in the treatment of erectile dysfunction secondary to spinal cord injury: a review of literature

Concept

Decreased sexual function is a major concern of men with spinal cord injuries (SCIs). Treatment of erectile dysfunction (ED) through oral pharmacotherapies has been proven to be an effective way to address and treat this concern.

Objective

To find an efficacious and satisfactory treatment ED secondary to SCI through the compilation of studies that utilized the International Index of Erectile Function (IIEF) when testing phosphodiesterase V inhibitors (PDE5i).

Method

Ten articles, which used the IIEF to study satisfaction and/or efficacy of PDE5is sildenafil, tadalafil, and vardenafil in the treatment of ED were reviewed and analyzed. Through the use of a self-made grading scale the value of each article was determined for this research.

Results

Sildenafil, tadalafil, and vardenafil all have been proven to be effective in treating ED in men with SCI. While sildenafil is the most thoroughly studied ED treatment for patients with SCI, tadalafil has a longer time duration effectiveness, which allows for more spontaneity in the sexual experience. Minimal adverse effects have been noted in patients with SCI using these medications; headache, flushing, and mild hypotension are the most common. In articles that study satisfaction, patients show great improvement over baseline with the use of these medications.

Conclusion

Although there is a need for further research on the safety in long-term use of tadalafil and vardenafil, comparative studies done on all three medications show no statistically significant difference in effectiveness or satisfaction. New medications and treatment options, such as avanafil, are being studied in hope of continued improvement of sexual function in men with SCI.     

Efficacy of tadalafil in the treatment of erectile dysfunction in hypertensive men on concomitant thiazide diuretic therapy

Many men with erectile dysfunction (ED) have hypertension as a comorbid condition. Recent guidelines recommend thiazide diuretics as first-line therapy for hypertension. We analyzed data from 14 randomized, double-blind, placebo-controlled trials (N=2501) to evaluate the efficacy of tadalafil 20 mg for the treatment of ED in men on thiazides. Of the 2501 patients, 163 were on concomitant thiazides (116 tadalafil/47 placebo) and 159 (98%) were reported to have hypertension. The primary efficacy measures were mean change from baseline in the international index of erectile function (IIEF) erectile function (EF) domain and the proportion of 'yes' responses to sexual encounter profile (SEP) Questions 2 and 3. The tadalafil group showed a significantly (P<0.001) greater mean baseline to endpoint improvement on all efficacy outcome measures compared to placebo-treated patients regardless of concomitant thiazide use. More importantly, the responses to tadalafil were similar regardless of concomitant thiazide use. Additionally, responses to tadalafil were comparable between thiazide and nonthiazide users regardless of baseline ED severity (P>0.05).     

An open-label, multicentre, randomized, crossover study comparing sildenafil citrate and tadalafil for treating erectile dysfunction in men naïve to phosphodiesterase 5 inhibitor therapy

Associate Editor Michael G. Wylie Editorial Board Ian Eardley, UK Jean Fourcroy, USA Sidney Glina, Brazil Julia Heiman, USA Chris McMahon, Australia Bob Millar, UK Alvaro Morales, Canada Michael Perelman, USA Marcel Waldinger, Netherlands

OBJECTIVES

To compare treatment preference, efficacy, and tolerability of sildenafil citrate (sildenafil) and tadalafil for treating erectile dysfunction (ED) in men naïve to phosphodiesterase 5 (PDE5) inhibitor therapy.

PATIENTS AND METHODS

This was an open‐label, crossover study of sildenafil and tadalafil (taken as needed). After a 4‐week baseline assessment, 367 men with ED (mean age 54 years) were randomized to receive sildenafil for 12 weeks followed by tadalafil for 12 weeks or vice versa (8‐week dose optimization and 4‐week assessment phases). During dose optimization, patients started taking 25‐ or 50‐mg sildenafil or 10‐mg tadalafil and could titrate to find their optimum dose (25‐, 50‐ or 100‐mg sildenafil; 10‐ or 20‐mg tadalafil). After completing both 12‐week periods, patients chose which treatment to continue during an 8‐week extension. Efficacy was measured with the International Index of Erectile Function (IIEF) and Sexual Encounter Profile (SEP) diary.

RESULTS

Of the 291 men who completed both treatments, 85 (29%) chose sildenafil and 206 (71%) chose tadalafil (P < 0.001) for the 8‐week extension. The IIEF erectile function domain scores were 14.2 at baseline, 23.9 at endpoint on sildenafil, and 24.3 at endpoint on tadalafil (P = 0.08, sildenafil vs tadalafil). The mean per patient percentage success scores for SEP2 (penetration) were: baseline (46%), sildenafil (post‐baseline 82%) and tadalafil (post‐baseline 85%; P = 0.06, sildenafil vs tadalafil), and for SEP3 (successful intercourse) were: baseline (19%), sildenafil (post‐baseline 72%), and tadalafil (post‐baseline 77%; P = 0.003, sildenafil vs tadalafil). The only treatment‐emergent adverse events that were reported by >5% of men were headache and flushing.

CONCLUSIONS

In men with ED who were naïve to PDE5 inhibitor therapy, sildenafil and tadalafil were both effective and well tolerated. After treatment with sildenafil and tadalafil, 29% of men chose sildenafil and 71% chose tadalafil for ED therapy during an 8‐week extension.

     

Combination of alfuzosin and sildenafil is superior to monotherapy in treating lower urinary tract symptoms and erectile dysfunction

OBJECTIVES: This pilot study was undertaken to assess the efficacy and safety of the alpha(1)-blocker alfuzosin 10mg once daily (OD), the PDE-5 inhibitor sildenafil 25mg OD, and the combination of both on lower urinary tract symptoms (LUTS) suggestive of benign prostatic hyperplasia (BPH) and erectile dysfunction (ED). MATERIAL AND METHODS: Men aged 50-76 yr with previously untreated LUTS and ED were randomized to receive alfuzosin (n=20), sildenafil (n=21), or the combination of both (n=21) for 12 wk. Changes from baseline in International Prostate Symptom Score (IPSS), voiding diary, maximum urinary flow rate (Qmax), postvoid residual urine (PVRU) volume, and erectile function domain of the International Index of Erectile Function (IIEF) were assessed at week 12. RESULTS: Improvement of IPSS was significant with the three treatments but greatest with the combination (-24.1%) compared with alfuzosin (-15.6%) and sildenafil (-11.8%) [corrected] alone (p<0.03). Frequency, nocturia, PVR, and Qmax were significantly improved with alfuzosin only and the combination. Improvement in IIEF was slight with alfuzosin (16.7%), marked with sildenafil (49.7%), and greatest with the combination (58.6%). Likewise, increases in the frequency of penetration (Q3) and of maintained erection (Q4) were greater with the combination therapy (65.2% and 68.2%, respectively) than with sildenafil (41.7% and 59.1%, respectively) and alfuzosin (27.3% and 33.3%, respectively) alone. All three treatments were well tolerated. CONCLUSIONS: In this pilot study, the combination of alfuzosin 10 mg OD and sildenafil 25 mg OD is safe and more effective than monotherapy with either agent to improve both voiding and sexual dysfunction in men with LUTS suggestive of BPH.     

An open-label,multicenter, randomized,crossover study comparing sildenafil citrate and tadalafil for treating erectile dysfunction in Chinese men na?ve to phosphodiesterase 5 inhibitor therapy

The study was to compare treatment preference, efficacy, and tolerability of sildenafil citrate (sildenafil) and tadalafil for treating erectile dysfunction (ED) in Chinese men naïve to phosphodiesterase 5 (PDE5) inhibitor therapies. This multicenter, randomized, open-label, crossover study evaluated whether Chinese men with ED preferred 20-mg tadalafil or 100-mg sildenafil. After a 4 weeks baseline assessment, 383 eligible patients were randomized to sequential 20-mg tadalafil per 100-mg sildenafil or vice versa for 8 weeks respectively and then chose which treatment they preferred to take during the 8 weeks extension. Primary efficacy was measured by Question 1 of the PDE5 Inhibitor Treatment Preference Questionnaire (PITPQ). Secondary efficacy was analyzed by PITPQ Question 2, the International Index of Erectile Function (IIEF) erectile function (EF) domain, sexual encounter profile (SEP) Questions 2 and 3, and the Drug Attributes Questionnaire. Three hundred and fifty men (91%) completed the randomized treatment phase. Two hundred and forty-two per 350 (69.1%) patients preferred 20-mg tadalafil, and 108/350 (30.9%) preferred 100-mg sildenafil (P < 0.001) as their treatment in the 8 weeks extension. Ninety-two per 242 (38%) patients strongly preferred tadalafil and 37/108 (34.3%) strongly the preferred sildenafil. The SEP2 (penetration), SEP3 (successful intercourse), and IIEF-EF domain scores were improved in both tadalafil and sildenafil treatment groups. For patients who preferred tadalafil, getting an erection long after taking the medication was the most reported reason for tadalafil preference. The only treatment-emergent adverse event reported by > 2% of men was headache. After tadalafil and sildenafil treatments, more Chinese men with ED naïve to PDE5 inhibitor preferred tadalafil. Both sildenafil and tadalafil treatments were effective and safe.     

根治性前列腺切除术后勃起功能障碍的PDE5抑制剂治疗现状

前列腺癌根治性前列腺切除术(RRP)术后勃起功能障碍(ED)的发生率10%~100%,保留神经的根治性前列腺切除术(NS-RRP)术后ED也超过三分之一。5型磷酸二酯酶(PDE5)抑制剂可用于各种原因ED的治疗。西地那非、伐地那非和他达拉非临床应用显示对RRP术后勃起功能的治疗有相似的作用,保留双侧神经的患者,服用西地那非的有72%的成功勃起率(阴道插入);服用伐地那非20 mg和10 mg的反应率是71.1%和59.7%;服用他达拉非的所有患者,平均成功的插入率是54%,平均成功性交率是41%,术后有某种程度勃起的患者,平均成功的插入率和成功性交率是69%和52%。但未有三者对RRP术后ED治疗的直接比较。     

Molecular mechanisms and pharmacokinetics of phosphodiesterase-5 antagonists

The prominence of phosphodiesterase-5 (PDE-5) inhibitors in the treatment of male erectile dysfunction and other diseases related to vascular dysfunction mandates a comprehensive understanding of the properties and effects of these compounds. Three potent and selective PDE-5 inhibitors (sildenafil, tadalafil, and vardenafil) have been approved for clinical use. The clinical efficacy and safety profiles of these medications are related to their molecular mode of action, the selectivity for PDE-5, and the pharmacokinetic properties (absorption, bioavailability, time to onset of action, distribution, metabolism, and elimination). These PDE-5 inhibitors share some common properties with regard to mechanisms of action and selectivities for PDE-5. They also have distinctive characteristics that may impact their clinical use. This article focuses on the basic biochemistry of cyclic guanosine monophosphate signaling and the pharmacokinetic parameters that describe characteristics of drug action of these PDE-5 inhibitors in facilitating smooth muscle relaxation, leading to improved penile erectile response or causing side effects.