Past, present, and future: a 7-year update of Viagra (sildenafil citrate)

ORIGINAL RESEARCH—ED PHARMACOTHERAPY: Do Food and Dose Timing Affect the Efficacy of Sildenafil? A Randomized Placebo‐Controlled Study

INTRODUCTION

Sildenafil citrate has been used worldwide by men with erectile dysfunction. The prescribing information for sildenafil suggests ingestion 1 hour before sexual activity and also notes reduced maximum plasma concentration and delayed time to maximum concentration following ingestion with a high-fat meal. The clinical impact of coingestion of food and these factors has never been evaluated.

AIM

To determine, using a naturalistic study design, whether sildenafil taken 1 hour before or during a meal compared with usual ingestion 30-60 minutes before sexual activity affects efficacy or patient satisfaction.

METHODS

After a 1-2-week washout, 48 men (29-79 years old), currently satisfied with sildenafil, followed each of four regimens: (A) sildenafil 1 hour before a meal and placebo 30-60 minutes before planned coitus vs. (B) placebo 1 hour before a meal and sildenafil 30-60 minutes before coitus; and (C) sildenafil during a meal and placebo 30-60 minutes before coitus vs. (D) placebo during a meal and sildenafil 30-60 minutes before coitus. Subjects were not instructed to change their regular dietary habits during the course of the study.

MAIN OUTCOME MEASURES

Change from baseline in the International Index of Erectile Function (IIEF) Erectile Function (EF) domain score, responses to Sexual Encounter Profile (SEP) questions 2 (erection sufficient for penetration) and 3 (erection sufficient to complete intercourse), and measures of patient preference and satisfaction.

RESULTS

Mean changes in IIEF-EF domain scores were 11.4 for regimens A and B and 11.2 for C and D. Positive SEP2 responses were recorded for 93.9% and 91.8% of intercourse attempts in A and B and 91.4% and 92.6% in C and D. Corresponding results for SEP3 were 84.7% and 85.9%, and 83.4% and 87.5%, respectively. There were no significant differences between pairs of treatments on satisfaction. The time between sildenafil ingestion and intercourse attempt (0-0.5 to >10 hours) had no significant effect on responses to SEP2, but decreased responses to SEP3 from a maximum of 92.8% at 1.5-2 hours to 81.6% at more than 10 hours (P = 0.003).

CONCLUSIONS

No significant loss of efficacy occurs when sildenafil is taken shortly before or with a meal. The duration of action for sildenafil may exceed 10 hours.

hMaxi-K Gene Transfer in Males with Erectile Dysfunction: Results of the First Human Trial

Eleven patients with moderate to severe erectile dysfunction (ED) were given a single-dose corpus cavernosum injection of hMaxi-K, a "naked" DNA plasmid carrying the human cDNA encoding hSlo (for human slow-poke), the gene for the alpha, or pore-forming, subunit of the human smooth muscle Maxi-K channel. Three patients each were given 500, 1000, and 5000 microg, and two patients were given 7500 microg, of hMaxi-K and monitored for 24 weeks. The primary objectives of this phase I study were safety and tolerability of escalating hMaxi-K doses as assessed by clinical evaluations and laboratory tests. Secondary efficacy objectives were measured primarily by use of the International Index of Erectile Function (IIEF) scale. Patient responses were validated by partner responses. There were no serious adverse events and no dose-related adverse events attributed to gene transfer for any patient at any dose or study visit. No clinically significant changes from baseline were seen in physical evaluations (general and genitourinary), hematology, chemistry, and hormone analyses, or in cardiac events evaluated by repeated electrocardiograms. Importantly, no plasmid was detected in the semen of patients at any time after the injections. Patients given the two highest doses of hMaxi-K had apparent sustained improvements in erectile function (EF) as indicated by improved IIEF-EF domain scores over the length of the study. One patient given 5000 microg and one given 7500 microg reported EF category improvements that were highly clinically significant and were also maintained through the 24 weeks of study. Efficacy conclusions cannot be drawn from results of a phase I trial with no control group. However, the promising primary safety outcomes of the study and preliminary indications of effectiveness provide evidence that hMaxi-K gene transfer is a viable approach to the treatment of ED and that further studies investigating the efficacy of hMaxi-K in patients with ED should be performed.

Sildenafil: from angina to erectile dysfunction to pulmonary hypertension and beyond

In less than 20 years, the first selective type 5 phosphodiesterase inhibitor, sildenafil, has evolved from a potential anti-angina drug to an on-demand oral treatment for erectile dysfunction (Viagra), and more recently to a new orally active treatment for pulmonary hypertension (Revatio). Here we describe the key milestones in the development of sildenafil for these diverse medical conditions, discuss the advances in science and clinical medicine that have accompanied this journey and consider possible future indications for this versatile drug.

Mechanisms of direct relaxant effect of sildenafil, tadalafil and vardenafil on corpus cavernosum

Sildenafil, tadalafil, vardenafil and verapamil induced concentration-dependent relaxation of the rabbit corpus cavernosum muscle precontracted with noradrenaline. The maximal relaxation (%) at 20 microM was 61.4 +/- 6.9, 32.4 +/- 5.4, 100.0 +/- 5.5 and 86.6 +/- 5.1 (n = 5 each) respectively. Pre-incubation of cavernosal muscle strips with N(omega)-nitro-L-arginine or guanylate cyclase inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) but not adenylate cyclase inhibitor, cis-N-[2-phenylcyclopentyl]-azacyclotridec-1-en-2-amine] (MDL12330A) culminated in only a 20-30% reduction in muscle relaxant action of the 3 phosphodiesterase inhibitors. This suggests that another mechanism of relaxation independent of nitric oxide-cGMP or cAMP pathway was involved. Higher concentrations of sildenafil (100 microM) and vardenafil (10 and 100 microM) produced non-competitive antagonism of noradrenaline-induced contraction characterized by reduced maximal effect. In contrast, tadalafil was devoid of significant effect on noradrenaline. On K(+)-depolarized tissues, sildenafil was as potent as vardenafil whereas tadalafil was the least effective in relaxing K(+)-induced tone. The maximal relaxation (% of K(+)-induced tone) at 20 microM sildenafil, tadalafil and vardenafil was respectively 84.1 +/- 6.5, 9.0 +/- 19.9, and 88.9 +/- 6.2 (n = 5 each). In addition, verapamil, sildenafil and vardenafil were more efficacious than tadalafil in reversing tonic contractions by Ca(2+) channel activator, 1,4,dihydro-2,6-dimethyl-5-nitro-4-[2(triflouromethyl)phenyl]pyridine-3-carboxylic acid methyl ester (BAY K-8644). These results indicate that vardenafil and sildenafil possess direct muscle relaxant potential possibly via inhibiting Ca(2+) influx through both receptor-operated and voltage-dependent Ca(2+) channels whereas tadalafil appears capable of inhibiting receptor-operated transmembrane Ca(2+) entry only.

The second Princeton consensus on sexual dysfunction and cardiac risk: new guidelines for sexual medicine

INTRODUCTION

Erectile dysfunction (ED) is a highly prevalent disorder associated with a significant burden of illness. The prevalence and incidence of ED are strongly age-related, affecting more than half of men >60 years. The first Princeton Consensus Conference (Princeton I) in 1999 developed guidelines for safe management of cardiac patients regarding sexual activity and the treatment of ED.

AIM

The second conference (Princeton II) was convened to update the recommendations based on the expanding knowledge base and new treatments available. This article reviews and expands on the Princeton II guidelines to address sexual dysfunction and cardiac risk.

METHODS

A consensus panel of experts reviewed recent multinational studies in safety and drug interaction data for three phosphodiesterase type 5 (PDE5) inhibitors (sildenafil, tadalafil, vardenafil), with emphasis on the safety of these agents in men with ED and concomitant cardiovascular disease.

RESULTS

Erectile dysfunction is an early symptom or harbinger of cardiovascular disease, due to the common risk factors and pathophysiology mediated through endothelial dysfunction. Major comorbidities include diabetes, hypertension, hyperlipidemia and heart disease. Any asymptomatic man who presents with ED that does not have an obvious cause (e.g., trauma) should be screened for vascular disease and have blood glucose, lipids, and blood pressure measurements. Ideally, all patients at risk but asymptomatic for coronary disease should undergo an elective exercise electrocardiogram to facilitate risk stratification. Lifestyle intervention in ED, specifically weight loss and increased physical activity, particularly in patients with ED and concomitant cardiovascular disease, is literature-supported.

CONCLUSIONS

The recognition of ED as a warning sign of silent vascular disease has led to the concept that a man with ED and no cardiac symptoms is a cardiac (or vascular) patient until proven otherwise. Men with ED and other cardiovascular risk factors (e.g., obesity, sedentary lifestyle) should be counseled in lifestyle modification.