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

Drug Repurposing of Voglibose, a Diabetes Medication for Skin Health

Background/Objectives: Voglibose, an α-glucosidase inhibitor commonly prescribed to manage postprandial hyperglycemia in diabetes mellitus, demonstrates potential for repurposing as an anti-melanogenic agent. This study aims to explore the inhibitory effects of voglibose on melanogenesis and elucidate its molecular mechanisms, highlighting its possible applications in treating hyperpigmentation disorders. Methods: The anti-melanogenic effects of voglibose were investigated using B16F10 melanoma cells. Cell viability, melanin content, and tyrosinase activity were assessed following voglibose treatment. Western blot analysis was performed to examine changes in melanogenic proteins and transcription factors. The role of signaling pathways, including PKA/CREB, MAPK, PI3K/AKT, and GSK3β/β-Catenin, was analyzed. Primary human skin irritation tests were conducted to evaluate the topical safety of voglibose. Results: Voglibose significantly reduced melanin synthesis and tyrosinase activity in B16F10 cells in a dose-dependent manner. Western blot analysis revealed decreased expression of MITF, TRP-1, and TRP-2, indicating the inhibition of melanogenesis. Voglibose modulated key signaling pathways, including the suppression of PKA/CREB, MAPK, and AKT activation, while restoring GSK3β activity to inhibit β-catenin stabilization. Human skin irritation tests confirmed voglibose's safety for topical application, showing no adverse reactions at 50 and 100 μM concentrations. Conclusions: Voglibose demonstrates anti-melanogenic properties through the modulation of multiple signaling pathways and the inhibition of melanin biosynthesis. Its safety profile and efficacy suggest its potential as a repurposed drug for managing hyperpigmentation and advancing cosmeceutical applications.

Investigating the therapeutic promise of drug-repurposed-loaded nanocarriers: A pioneering strategy in advancing colorectal cancer treatment

Globally, colorectal cancer is a major health problem that ranks in third place in terms of occurrence and second in terms of mortality worldwide. New cases increase annually, with the absence of effective therapies, especially for metastatic colorectal cancer, emphasizing the need for novel therapeutic approaches. Although conventional treatments are commonly used in oncotherapy, their success rate is low, which leads to the exploration of novel technologies. Recent efforts have focused on developing safe and efficient cancer nanocarriers. With their nanoscale properties, nanocarriers have the potential to utilize internal metabolic modifications amid cancer and healthy cells. Drug repurposing is an emerging strategy in cancer management as it is a faster, cheaper, and safer method than conventional drug development. However, most repurposed drugs are characterized by low-key pharmacokinetic characteristics, such as poor aqueous solubility, permeability, retention, and bioavailability. Nanoparticles formulations and delivery have expanded over the past few decades, creating opportunities for drug repurposing and promises as an advanced cancer modality. This review provides a concise and updated overview of colorectal cancer treatment regimens and their therapeutic limitations. Furthermore, the chemotherapeutic effect of various FDA-approved medications, including statins, non-steroidal anti-inflammatory drugs, antidiabetic and anthelmintic agents, and their significance in colorectal cancer management. Along with the role of various nanocarrier systems in achieving the desired therapeutic outcomes of employing these redefined drugs.

Safety assessment of sildenafil use in neonates: a real-world data analysis based on the FDA adverse event reporting system (FAERS)

BACKGROUND

The safety of neonatal sildenafil use remains uncertain. This study aimed to investigate adverse events (AEs) associated with sildenafil use in neonates.

RESEARCH DESIGN AND METHODS

We collected data on AEs associated with sildenafil use in neonates from the US Food and Drug Administration Adverse Event Reporting System database, spanning from its inception of the database in 2004 to 2023. Disproportionality measures were employed to analyze the correlation between AEs and sildenafil.

RESULTS

Sildenafil was identified as the primary suspect drug in 75 AE reports, involving 214 AEs. Three system organ classes, namely, eye disorders, hepatobiliary disorders, and vascular disorders were associated with sildenafil use. Six preferred terms, namely, flushing, retinopathy of prematurity, hyperbilirubinemia, pulmonary hemorrhage, hypotension, and diarrhea were associated with sildenafil use. Notably, hyperbilirubinemia and pulmonary hemorrhage were previously unreported AEs associated with sildenafil use.

CONCLUSION

The results highlight the ongoing uncertainty surrounding the safety of neonatal sildenafil use and provide vital support for risk monitoring and identification in neonates receiving sildenafil. Additionally, the study underscores the need for continuous safety surveillance in neonates treated with sildenafil and suggests further exploration of the precise causal relationships between AEs and sildenafil.

Exploring the Multifaceted Potential of Sildenafil in Medicine

Phosphodiesterase type 5 (PDE5) is pivotal in cellular signalling, regulating cyclic guanosine monophosphate (cGMP) levels crucial for smooth muscle relaxation and vasodilation. By targeting cGMP for degradation, PDE5 inhibits sustained vasodilation. PDE5 operates in diverse anatomical regions, with its upregulation linked to various pathologies, including cancer and neurodegenerative diseases. Sildenafil, a selective PDE5 inhibitor, is prescribed for erectile dysfunction and pulmonary arterial hypertension. However, considering the extensive roles of PDE5, sildenafil might be useful in other pathologies. This review aims to comprehensively explore sildenafil's therapeutic potential across medicine, addressing a gap in the current literature. Recognising sildenafil's broader potential may unveil new treatment avenues, optimising existing approaches and broadening its clinical application.

In vitro high glucose increases apoptosis, decreases nerve outgrowth, and promotes survival of sympathetic pelvic neurons

Background

Diabetes mellitus (DM) is a common cause of erectile dysfunction (ED), yet the molecular basis of DM neurogenic ED remains unknown.

Aim

In this study we examined the impact of high glucose on survival and growth of primary cultured pelvic neurons in a rat model and assessed whether coculturing with healthy Schwann cells (SCs) can rescue pelvic neuron growth in patients with DM.

Methods

Major pelvic ganglia (MPGs) from adult male Sprague Dawley rats (n = 8) were dissociated and plated on coverslips. Neurons were exposed to high glucose (45 mM) for 24 or 48 hours and compared to time-matched controls (25 mM). Neurons were stained for neuron-specific beta-tubulin, neuronal nitric oxide synthase, vesicular acetylcholine transferase, tyrosine hydroxylase, and TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling) assay. Schwann cells were dissociated from MPGs of healthy male Sprague Dawley rats (n = 4) and grown to confluence. Additional Sprague Dawley rats were made diabetic with streptozotocin (50 mg/kg, n = 4), and 5 weeks later MPGs were collected from these rats, dissociated, and cocultured on healthy SCs. Neurons and SCs were stained with beta-tubulin and S100.

Outcomes

Length, branching, and survival of nitrergic, parasympathetic, and sympathetic neurons was assessed in neurons exposed to normal or high glucose concentrations, and neuron length was measured in neuron-SC coculture.

Results

The total number of neurons and the length and number of branches were significantly decreased after 24 and 48 hours of high glucose (P < .05). The percentage of nitrergic neurons decreased 10% after 24 hours and 50% after 48 hours of high glucose (P < .05). After 24 hours of high glucose, cholinergic-positive neurons were unchanged; however, these neurons decreased 30% after 48 hours (P < .05). The proportion of sympathetic neurons increased 25% after 48 hours of high glucose (P < .05). At both timepoints, there was a 2-fold increase in the total apoptotic neurons with high glucose (P < .05). Neurite outgrowth recovered to control lengths after coculture of diabetic neurons with healthy SCs (P < .05).

Clinical Translation

Glucose can be used as a tool to investigate the direct effects of DM on neuritogenesis. Our data suggest that an effective treatment for DM ED protects and repairs the penile neuronal supply.

Strengths and Limitations

Exposing MPG neurons to high glucose offers a quick and, inexpensive proxy for DM-related conditions. A limitation of our study is that our model reflects type 1 DM, whereas clinically, most diabetic ED patients have type 2 DM.

Conclusion

Culturing pelvic neurons in high glucose can be used as a tool to elucidate how to protect proerectile neurons from cell death and may lead to new therapeutic strategies for diabetic men suffering from ED.

Changes in the Pharmacokinetics and Pharmacodynamics of Sildenafil in Cigarette and Cannabis Smokers

Sildenafil citrate, a widely-used oral therapy for erectile dysfunction, is a cytochrome P3A4 (CYP3A4) enzyme substrate. Studies have reported that this substrate has an inhibitory effect on CYP3A4 enzymes in long-term cigarette and cannabis smokers, which predominantly mediate the hepatic elimination of sildenafil. Cigarette and/or cannabis smoking could therefore alter the exposure of sildenafil. The aim of this study was to examine the effect of smoking cigarettes and/or cannabis on the pharmacokinetics, pharmacodynamics, safety and tolerability of sildenafil. Thirty-six healthy human subjects were equally divided into three groups: non-smokers, cigarette smokers and cannabis smokers. Each group was administered a single dose of sildenafil (50 mg tablets). The primary outcome measures included the maximum concentration of sildenafil in plasma (C_max), the elimination half-life (t1/2) and the area under the plasma concentration time curve from zero to time (AUC_0-t). The pharmacodynamics were assessed by the International Index of Erectile Function (IIEF-5). The exposure of sildenafil (AUC_0-t) showed a statistically significant increase in cigarette smokers (1156 ± 542 ng·h/mL) of 61% (p < 0.05) while in cannabis smokers (967 ± 262 ng·h/mL), a non-significant increase in AUC_0-t of 35% (p > 0.05) was observed relative to non-smokers (717 ± 311 ng·h/mL). Moreover, the C_max of sildenafil increased by 63% (p < 0.05) and 22% (p > 0.05) in cigarette smokers and cannabis smokers, respectively. Cigarette smoking increases the exposure of sildenafil to a statistically significant level with no effect on its pharmacodynamics, safety and tolerability.

Sildenafil beyond erectile dysfunction and pulmonary arterial hypertension: Thinking about new indications

Sildenafil, approved two decades ago, is the inhibitor of phosphodiesterase 5 (PDE5). First of all, it was designated for angina pectoris, but soon it showed a wonderful efficacy in erectile dysfunction (ED) and then pulmonary arterial hypertension (PAH). Due to the distribution of phosphodiesterase (PDE) in almost all organs, maybe it effects other diseases. Hence, a great number of investigations began to understand the role of PDEi in different organs. Preliminary research on sildenafil in cell culture and animal models has yielded promising results. Soon, a greater number of animal researches and clinical trials joined them. The results disclosed sildenafil can have beneficial effects in each organ such as heart, liver, kidney, brain, and intestines. Furthermore, it has significantly improved the prognosis of organ ischemia in various animal models. Clinical trials in several diseases, such as recurrent spontaneous miscarriage, fatty liver disease, bronchopulmonary dysplasia (BPD), heart failure, and premature ejaculation (PE) brought promising results. Although some clinical trials are available on the effects of sildenafil on various diseases, further studies on humans are needed to consolidate the ultimate effects of sildenafil. The aim of this review was to describe the effects of sildenafil on each organ and explain its mechanisms of action. Further, other PDE inhibitors such as tadalafil and vardenafil have been briefly discussed in parts of this review.

Drug adulteration of sexual enhancement supplements: a worldwide insidious public health threat

Worldwide, the consumption of dietary supplements for the enhancement of sexual performance is common. Consumers are generally fond of these products because they often want to avoid drugs, preferring "natural" than "chemical" solutions. This is challenging, as many of these supplements labelled "herbal" or "natural" are actually adulterated with drugs, mainly phosphodiesterase-5 inhibitors. This phenomenon is facilitated by fewer demanding regulations for marketing supplements. Thus, consumers may be widely exposed to serious adverse events, such as acute liver injury, kidney failure, pulmonary embolism, stroke or even death. We aim to warn physicians about this issue. This multidisciplinary review simultaneously deals with clinical consequences of this phenomenon, analytical toxicology and regulation. Indeed, after outlining this worldwide issue and highlighting that a drug-adulterated dietary supplement is actually a falsified drug, we discuss its main contributing factors. Then, we describe some examples of adverse events of which a case of sildenafil-tadalafil-induced ischaemic stroke that benefited medical care in our hospital. Furthermore, we present some means to avoid adulteration and discuss their limitations that may be explained by the heterogeneity of the regulation of dietary supplements between countries. Doing so, we point out the requirement of a global harmonization of this regulation for an efficient eradication of this public health threat. Meanwhile, dietary supplements should be considered adulterated until proven otherwise. Thus, we encourage physicians to investigate these products in the drug histories of their patients, especially when clinical conditions cannot be explained by classical aetiologies.

New Approaches in Oncology for Repositioning Drugs: The Case of PDE5 Inhibitor Sildenafil

The use of already-approved drugs to treat new or alternative diseases has proved to be beneficial in medicine, because it reduces both drug development costs and timelines. Most drugs can be used to treat different illnesses, due their mechanisms of action are not restricted to one molecular target, organ or illness. Diverging from its original intent offers an opportunity to repurpose previously approved drugs to treat other ailments. This is the case of sildenafil (Viagra), a phosphodiesterase-5 (PDE5) inhibitor, which was originally designed to treat systemic hypertension and angina but is currently commercialized as erectile dysfunction treatment. Sildenafil, tadalafil, and vardenafil are PDE5 inhibitors and potent vasodilators, that extend the physiological effects of nitric oxide and cyclic guanosine monophosphate (cGMP) signaling. Although most of the biological implications of these signaling regulations remain unknown, they offer a large therapeutic potential for several diseases. In addition, some PDE5 inhibitors' molecular effects seem to play a key role in different illnesses such as kidney disease, diabetes mellitus, and cancer. In this review, we discuss the molecular effects of PDE5 inhibitors and their therapeutic repurposing in different types of cancer.

Behavioral and hormonal effects of prolonged Sildenafil treatment in a mouse model of chronic social stress

Chronic social defeat can inhibit the reproductive system of subordinate males and causes behavioral deficits. Sildenafil treatment increases mice testosterone levels through its effects on Leydig cells of mice and it has been found to work as an antidepressant drug both in humans and in animal models. Since previous findings showed that sildenafil can counteract the inhibitory effects of chronic social defeat on agonistic, reproductive and anxiety-like behaviors of subordinate male mice, we investigated whether these behavioral outcomes can be explained by Sildenafil stimulation of testosterone. CD1 mice underwent an intruder-resident paradigm. After the fifth day of test, subordinate mice were injected with either a 10 mg/kg Sildenafil or a saline solution for 4 weeks. The results of the present study showed that Sildenafil treatment increased counterattacking behaviors and sexual motivation of subordinate males in addition to limiting the increase in body weight often observed in subordinate mice following chronic psychosocial stress. Moreover, sildenafil treated mice showed a pattern of behaviors reflecting lower anxiety. In agreement with previous studies, Sildenafil also increased testosterone levels. These data demonstrate that sildenafil can counteract the effects of chronic stress, possibly through its stimulatory effects on Leydig cells. These data demonstrate that sildenafil might counteract the effects of chronic psychosocial stress through centrally and peripherally mediated mechanisms.

Sexual dysfunction or sexual discipline? Sexuopharmaceutical use by men as prevention and proficiency

In the first decade following Viagra’s appearance, feminist and critical scholars documented the sexuopharmaceutical expansion of definitions of erectile dysfunction and its target consumer. As we approach Viagra’s 30th anniversary, while feminist scholarship on the medicalization of sexuality flourishes, the impact of erectile medication has received much less attention. This paper (re)casts a critical lens on popularized erectile medication sexual health messages in the context of current pharmaceutical marketing targeting users as neoliberal aspirational sexual subjects. Discourse analysis reveals that online advice about erectile medication use leverages the increased preoccupation with health risk assessment and prevention technologies to normalize erectile dysfunction as a risk for all men, irrespective of age and health status. Erectile dysfunction is presented as inevitable, pathological, and requiring vigilance and expert consultation; penile performance acts as a predictive health gauge. Erectile medication users are situated as model masculine subjects, (medically) augmenting sexual proficiency in romantic or sexually experimental contexts.

Off-Label Use of Phosphodiesterase Type 5 Inhibitor Erectile Dysfunction Medication to Enhance Sex Among Gay and Bisexual Men in Australia: Results From the FLUX Study

BACKGROUND

Gay and bisexual men (GBM) use oral erectile dysfunction medications (EDMs) often with little evidence of medical indication necessitating their use.

AIM

To investigate the prevalence, contexts, and motivations for oral EDM use and its relation to sexual risk behavior.

METHODS

A total of 2,250 Australian GBM completed an online survey of licit and illicit drug use and their associated behaviors. Multivariate logistic regression analysis identified factors associated with use of EDMs in the previous 6 months and, for those who had used EDMs, factors associated with use on a weekly basis.

OUTCOMES

Any EDM use and at least weekly use in the previous 6 months.

RESULTS

The median age of the sample was 33.0 years (range = 16-81). Two thirds (67.7%) reported no lifetime history of EDM use. Approximately 1 in 10 participants (11.1%) had last used an EDM more than 6 months previously. In the previous 6 months, 11.5% reported using EDMs less than monthly, 5.3% reported using EDMs approximately monthly, and 4.5% reported using EDMs at least weekly. Of men who had used EDMs in the previous 6 months, common reasons cited for its use were to maintain an erection for longer (73.3%), to make it easier to "get hard" (67.3%), and difficulty in attaining or maintain an erection (53.5%). Use of EDMs in the previous 6 months was associated with illicit drug use and higher rates of sexual risk behavior. Weekly users were more likely to have severe anxiety than less frequent users.

CLINICAL TRANSLATION

The use of EDMs in the context of intensive sex partying, with the associated potential for increased risk of HIV transmission and illicit drug use, indicates a need to consider the use of EDMs among GBM in HIV prevention and minimizing harm.

STRENGTHS AND LIMITATIONS

This large-scale study of drug use among GBMs includes comprehensive detailed data on their history of use and rationales for use. Our online methodology potentially decreases social desirability bias in reporting illegal or stigmatized behaviors. This volunteer online convenience sample might not be representative of all GBMs in Australia.

CONCLUSION

GBMs who used an oral EDM in the previous 6 months often used it for recreational purposes, but many of those who used it on a weekly basis also might have used it for therapeutic reasons. GBMs often use EDMs to enhance their sexual experiences often in the context of intensive sex partying (which can include risky sexual behavior). Hammoud MA, Jin F, Lea T, et al. Off-Label Use of Phosphodiesterase Type 5 Inhibitor Erectile Dysfunction Medication to Enhance Sex Among Gay and Bisexual Men in Australia: Results From the FLUX Study. J Sex Med 2017;14:774-784.

Propping up pharma's (natural) neoliberal phallic man: pharmaceutical representations of the ideal sexuopharmaceutical user

Contemporary social theorists emphasise the cultural quest for authenticity under conditions of increasing artificiality. Within this context, the body is commonly treated as an 'unfinished' surface requiring ongoing transformation to fulfil identity obligations. In this paper, we examine one such identity authentication project in the form of marketing of men's sexuopharmaceuticals. We use online pharmaceutical advertising for four approved sexuopharmaceuticals (Viagra, Cialis, STAXYN and Stendra) to describe the ideal neoliberal consumer. These campaigns underscore the robust role of pharmaceuticals in sexual authentication projects undergirded by neoliberal consumerist and aspirationalist ideals. Penile dependability as a luxury consumerist project reinvigorates traditional sexual (masculine) authentication as yoked to phallic control, by repackaging sexual enhancement medication use as a neoliberal beacon of aspirational achievements. The ideal targeted user is increasingly younger, and consumption of sexuopharmaceuticals is represented as achieving elite status and exclusive pleasures; masculine authenticity and choice; progressive relationships and a contemporary urban, fast-paced life; and a prepared yet spontaneous romantic sexuality. Women are also increasingly used in promotional materials directed at men; their responsibility centres on coaching and coaxing potential users.

Concise Review: Fat and Furious: Harnessing the Full Potential of Adipose-Derived Stromal Vascular Fraction

Due to their capacity to self-renew, proliferate and generate multi-lineage cells, adult-derived stem cells offer great potential for use in regenerative therapies to stop and/or reverse degenerative diseases such as diabetes, heart failure, Alzheimer's disease and others. However, these subsets of cells can be isolated from different niches, each with differing potential for therapeutic applications. The stromal vascular fraction (SVF), a stem cell enriched and adipose-derived cell population, has garnered interest as a therapeutic in regenerative medicine due to its ability to secrete paracrine factors that accelerate endogenous repair, ease of accessibility and lack of identified major adverse effects. Thus, one can easily understand the rush to employ adipose-derived SVF to treat human disease. Perhaps faster than any other cell preparation, SVF is making its way to clinics worldwide, while critical preclinical research needed to establish SVF safety, efficacy and optimal, standardized clinical procedures are underway. Here, we will provide an overview of the current knowledge driving this phenomenon, its regulatory issues and existing studies, and propose potential unmapped applications. Stem Cells Translational Medicine 2017;6:1096-1108.

The devil is in the details: an analysis of the subtleties between phosphodiesterase inhibitors for erectile dysfunction

Erectile dysfunction (ED) is a common sexual disorder with numerous etiologies involving multiple organ systems that leads to significant distress and decreased quality of life for the affected men. Fortunately, there are several modalities and interventions for treating ED. Oral medications, intra-urethral compounds, intracorporeal injections, vacuum-assist devices and surgically implanted prostheses are all part of the treatment algorithm. One of the first-lines and certainly the most widely used options for treating ED is the family of oral phosphodiesterase type 5 inhibitors (PDE5I). The introduction of these medications in the late 1990s revolutionized the field of sexual medicine. Currently there are no guidelines and minimal literature to help providers choose among drugs in this class. This review will address differences in efficacy and side effects between various members of the oral selective phosphodiesterase-5 inhibitor class of drugs.

Sildenafil Ameliorates Advanced Glycation End Products-Induced Mitochondrial Dysfunction in HT-22 Hippocampal Neuronal Cells

OBJECTIVE

Accumulation of advanced glycation end-products (AGE) and mitochondrial glycation is importantly implicated in the pathological changes of the brain associated with diabetic complications, Alzheimer disease, and aging. The present study was undertaken to determine whether sildenafil, a type 5 phosphodiesterase type (PDE-5) inhibitor, has beneficial effect on neuronal cells challenged with AGE-induced oxidative stress to preserve their mitochondrial functional integrity.

METHODS

HT-22 hippocampal neuronal cells were exposed to AGE and changes in the mitochondrial functional parameters were determined. Pretreatment of cells with sildenafil effectively ameliorated these AGE-induced deterioration of mitochondrial functional integrity.

RESULTS

AGE-treated cells lost their mitochondrial functional integrity which was estimated by their MTT reduction ability and intracellular ATP concentration. These cells exhibited stimulated generation of reactive oxygen species (ROS), disruption of mitochondrial membrane potential, induction of mitochondrial permeability transition, and release of the cytochrome C, activation of the caspase-3 accompanied by apoptosis. Western blot analyses and qRT-PCR demonstrated that sildenafil increased the expression level of the heme oxygenase-1 (HO-1). CoPP and bilirubin, an inducer of HO-1 and a metabolic product of HO-1, respectively, provided a similar protective effects. On the contrary, the HO-1 inhibitor ZnPP IX blocked the effect of sildenafil. Transfection with HO-1 siRNA significantly reduced the protective effect of sildenafil on the loss of MTT reduction ability and MPT induction in AGE-treated cells.

CONCLUSION

Taken together, our results suggested that sildenafil provides beneficial effect to protect the HT-22 hippocampal neuronal cells against AGE-induced deterioration of mitochondrial integrity, and upregulation of HO-1 is involved in the underlying mechanism.

Increased collagen maturity with sildenafil citrate: experimental high risk colonic anastomosis model

BACKGROUND

Inadequate healing and high anastomosis leak rates at rectal anastomosis may be due to lack of supportive serosal layer and technical difficulty of low anterior resections. Positive effects of sildenafil on wound healing were observed. The aim of this study was to simulate rectal anastomosis as a technical insufficient anastomosis and investigate the effects of sildenafil on anastomosis healing.

METHODS

Colonic anastomoses were carried out in 64 rats and randomized into four groups, CA-S, complete anastomoses without sildenafil (10 mg/kg for 5 days); CA+S, complete anastomoses with sildenafil; IA-S, incomplete anastomoses without sildenafil; IA+S, incomplete anastomoses with sildenafil. Half of the rats in every group were sacrificed on post-operative day (POD) 3, half of them sacrificed on POD 7. Tissues from the anastomoses were used for functional, histochemical, biochemical investigations.

RESULTS

Sildenafil treatment resulted in increased bursting pressures in IA+S on POD 7 (p=0.010). Collagen maturity was higher in IA+S on POD 3 and POD 7, CA+S on POD 7 (p=0.010; p=0.010; p<0.007). Collagen content was higher in IA+S on POD 7 (p<0.001). Glutathione, hydroxyproline levels were similar. Malondialdehyde levels were lower in IA+S on POD 3 (p<0.001). Epithelization score was higher in IA+S on POD 7 (p=0.007). Inflammation score was higher in CA-S group on POD 3 and POD 7 (p<0.001; p<0.001). Neutrophil score was lower in CA+S on POD 3 (p=0.005).

CONCLUSION

An increase in collagen content, maturity, and epithelization, a decrease in neutrophil infiltration, oxidative stress and better mechanical strength were observed with the administration of sildenafil.

Screening of aphrodisiac property in sea slug, Aplysia dactylomela

OBJECTIVE

To evaluate the aphrodisiac property of Aplysia dactylomela (A. dactylomelan), locally known as 'dugu-dugu', which is one of the sea slug species.

METHODS

Two types of extractions were used; aqueous and lipid. Three doses of each A. dactylomelan extract, respectively; 50, 100, 200 mg/kg were administered (i.p.) to male mice for mounting behavior test. Sildenafil citrate or Viagra® (5 mg/kg) being positive control while negative control received saline solution.

RESULTS

The animals treated with lipid extract at the respective dose exhibited mounting behavior, but the mounting frequency decreased at higher doses (100 and 200 mg/kg). However, all doses of aqueous extract did not show any mounting behavior. Meanwhile, in all doses of lipid extracts administered displayed significant difference (P<0.05) from the positive control. Despite this, only the lipid extract of 50 mg/kg showed significant difference (P<0.05) with negative control. This signifies that lipid extracts especially in dose 50 mg/kg have a substantial effect of aphrodisiac property. In addition, the presence of steroids was detected in the phytochemical screening of lipid extract.

CONLUSIONS

The findings from this study provides preliminary scientific evidence that A. dactylomela could be used as an alternative medication of natural product for promoting sexual activity in men.

Condom Attitudes of Heterosexual Men Ages 50 and Older Using Prescribed Drugs (Viagra, Cialis, Levitra) to Treat Erectile Dysfunction

The purpose of this study was to explore attitudes about condoms that may affect condom use by heterosexual men ages 50 and older who were sexually active and currently using prescribed oral phosphodiesterase type 5 inhibitor medications (Viagra®, Cialis®, or Levitra®) for treatment of erectile dysfunction. The study was part of a larger study that explored the need for safer-sex health promotion and education for these men. Fifty men completed factor subscales of the Condom Attitude Scale. Subscales were scored and analyzed. Positive factors were found with regard to the Interpersonal Impact, Inhibition, Perceived Risk, Perceived Seriousness, and Global Attitudes subscales. Factors with negative or neutral responses included the Effect on Sexual Experience, Relationship Safety, and Promiscuity subscales. Independent t tests revealed no differences between married and nonmarried men for the mean score on any of the subscales, but there was a difference on the Global Attitude Scale, with younger men having a more positive global attitude than older men. Study findings can be used in the development of health promotion educational activities on condom use as a safer-sex practice.

Sildenafil, a phosphodiesterase type 5 inhibitor, enhances the activity of two atypical antidepressant drugs, mianserin and tianeptine, in the forced swim test in mice

Sildenafil, a selective phosphodiesterase type 5 inhibitor, has recently been reported to abolish anti-immobility action of antidepressant drugs, i.e., bupropion, venlafaxine and S-citalopram, in the forced swim test in mice. The present study was designed to investigate the influence of sildenafil on the potential of two atypical antidepressants, namely mianserin and tianeptine. Swim sessions were conducted by placing mice in glass cylinders filled with water for 6 min and the duration of the behavioral immobility during the last 4 min of the test was evaluated. Locomotor activity was measured with photoresistor actimeters. To evaluate the potential pharmocokinetic interaction, total brain concentrations of the studied antidepressants were determined by HPLC method. Sildenafil at a dose of 2.5 mg/kg did not affect the activity of mianserin (20 mg/kg) in the forced swim test. Interestingly, at higher doses (5 and 10 mg/kg), sildenafil significantly enhanced the anti-immobility action of mianserin. Likewise, sildenafil (5, 10 and 20 mg/kg) robustly augmented the antidepressant activity of tianeptine (30 mg/kg). Mianserin alone, as well as in a combination with sildenafil at the highest dose, caused a potent reduction in locomotor activity. However, the changes in motor activity did not interfere with the data obtained in the forced swim test. Sildenafil significantly increased the total brain tianeptine concentration. No alteration in mianserin level in the brain after sildenafil co-administration was observed. The present study suggests that sildenafil enhances the activity of mianserin and tianeptine in the forced swim test in mice. The changes in the antidepressant activity of mianserin evoked by sildenafil co-administration were related to pharmacodynamic interaction while the interaction between tianeptine and sildenafil was, at least in part, pharmacokinetic in nature.

ADMET considerations for phosphodiesterase-5 inhibitors

INTRODUCTION

ADMET (absorption, distribution, metabolism, excretion, and toxicity) profiling is an important aspect of all drug developments. The pharmaceutical industry must always consider ADMET properties in order to optimize drug candidates and to introduce new formulations against existing marketed drugs. Consequently, candidate drug development may be halted early in the discovery phase or during the more costly drug development process because of their poor ADMET properties.

AREAS COVERED

The main focus of this article is ADMET profiling, pharmacokinetic (PK) drug interactions, mechanisms and possible adverse drug reactions (ADRs) for approved phosphodiesterase-5 inhibitors (PDE5Is). The authors also look at the efficacy and non-erectogenic benefits of current PDE5Is, which are widely used by patients with erectile dysfunction (ED). The authors also discuss other unapproved PDE5Is such as aildenafil and udenafil, which are currently in use in clinical trials.

EXPERT OPINION

The authors believe that the enhancing effect of PDE5Is on the nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) pathway means that PDE5Is could be used to treat various conditions. An important issue in their development is 'cross-talk' between PDE5 and other PDEs and thus their specificity for other PDEs. But while it might be difficult to achieve the ideal ADMET profile, it should not necessarily prevent further development of a lead PDE5I. The risk assessment of PDE5Is, with respect to their ADMET properties, is therefore very important for predicting drug-drug interactions, possible side effects, ADRs and its future clinical applications.

Phosphodiesterase-5 inhibitors: novel weapons against Alzheimer's disease?

Although Alzheimer's disease (AD) poses a major health problem in both developing and developed countries, no definite treatment is available for its cure; hence efforts are being focused on introducing disease-modifying agents for slowing down its course. Recent studies on the effects of sildenafil on different organs have shown that PDE-5 inhibitors may offer new horizons in therapeutic treatment of pulmonary hypertension, multiple sclerosis, neuropathic pain, and age-related memory impairment. In this paper we introduce PDE-5 inhibitors as novel disease-modifying agents against AD and review the different impacts of PDE-5 inhibition on various pathogenic mechanisms leading to AD, including neuronal apoptosis, neurovascular dysfunction, neurotransmitter modulation, and impairment of neurogenesis.

Pharmacokinetic-pharmacodynamic analysis of the static allodynia response to pregabalin and sildenafil in a rat model of neuropathic pain

The objective of this study was to develop a pharmacokinetic-pharmacodynamic (PK-PD) model of the static allodynia response to pregabalin with and without sildenafil in a chronic constriction injury model of neuropathic pain. Six treatment groups were evaluated every 30 min for 6 h. Rats were treated with either 1) a saline infusion; 2) a 2-h pregabalin infusion at 4 mgxkg(-1)xh(-1); 3) a 2-h pregabalin infusion at 10 mgxkg(-1)xh(-1); 4) a 2.2-mg loading dose + 12 mgxkg(-1)xmin(-1) infusion of sildenafil; 5) a 2-h pregabalin infusion at 1.6 mgxkg(-1)xh(-1) with sildenafil; and 6) a 2-h infusion of pregabalin at 4 mgxkg(-1)xh with sildenafil. The static allodynia endpoint was modeled by using three population PD approaches: 1) the behavior of the injured paw using a three-category ordinal logistic regression model; 2) paw withdrawal threshold (PWT) (g) between the injured and uninjured paw using the Hill equation with a baseline function; and 3) the baseline normalized difference in PWT between the injured and uninjured paw. The categorical model showed a significant shift in the concentration-response relationship of pregabalin to lower concentrations with concomitant sildenafil. Likewise, the continuous PK-PD models demonstrated a reduction in the EC(50) of pregabalin necessary for PD response in the presence of sildenafil. The difference-transformed PD model resulted in a 54.4% (42.3-66.9%) decrease in EC(50), whereas the percentage-transformed PD model demonstrated a 53.5% (42.7-64.3%) shift. It is concluded from these studies that there is a synergistic PD interaction between pregabalin and sildenafil.

Clinical use of sildenafil in pulmonary artery hypertension

Severe pulmonary hypertension is a debilitating disease with short life expectancy that often affects young people. It is usually idiopathic pulmonary artery hypertension and is characterized by progressive elevation of pulmonary artery pressure and vascular resistance, right ventricular failure and death with a limited median survival time. There is an imbalance in vasoconstrictive and vasodilatory substances. The phosphodiesterase-5 inhibitor sildenafil, a pulmonary and penile vasodilator initially approved for erectile dysfunction, is found to be efficacious in severe pulmonary artery hypertension. There are limited treatment options for the management of pulmonary artery hypertension in developing countries and sildenafil is a reasonable treatment option. This article reviews the relevant clinical data in pulmonary hypertension and the role of sildenafil in its management.

The effect of sildenafil citrate (Viagra) on cerebral blood flow in patients with cerebrovascular risk factors

OBJECTIVES

Sildenafil citrate is widely used for erectile dysfunction. The present study examined the short-term effects of sildenafil administration in individuals with cerebrovascular risk factors, including patients with a history of stroke.

MATERIALS AND METHODS

Twenty-five consecutive male patients with erectile dysfunction and vascular risk factors were included in the study. A perfusion brain SPECT study was performed at baseline and 1 h after the oral administration of sildenafil.

RESULTS

Associations between any of the risk factors and the perfusion scores were not detected, with the exception of stroke. Stroke patients showed significantly more areas with diminished perfusion after sildenafil administration compared to baseline.

CONCLUSIONS

In patients with diabetes or hypertension, a dose of 50 mg sildenafil does not appear to produce detrimental effects on cerebral blood flow. However, patients with a history of stroke may be at increased risk of hemodynamic impairment after the use of sildenafil.

Dose-dependent effects of sildenafil on post-ischaemic left ventricular function in the rat isolated heart

Objectives

Sildenafil may be beneficial during myocardial ischaemia/reperfusion, but this effect may be dose-dependent, accounting for previous conflicting results. We have explored the effects of two acute and one chronic administration regimen on left ventricular function.

Methods

The study was conducted on 36 Wistar rats (290 ± 7 g). Sildenafil was administered 30 min before ischaemia at a low (0.7 mg/kg, n= 8) or high (1.4 mg/kg, n= 8)dosage. The chronic treatment arm (n= 8) consisted of two daily injections of sildenafil (0.7 mg/kg) for three weeks. The control group was formed by 12 rats. Ischaemic contracture, post-ischaemic recovery and hypercontracture were measured in isolated, Langendorff-perfused preparations.

Key findings

Ischaemic contracture tended to be lower after high-dose sildenafil, while remaining unchanged after low-dose or chronic sildenafil administration. Compared with controls (62.9 ± 2.0% of baseline developed pressure), post-ischaemic recovery was higher (P= 0.0069) after low dose (75.1 ± 2.4%), unchanged (P= 0.13) after high dose (69.1 ± 2.1%), but lower (P &lt; 0.001) after chronic (42.9 ± 4.5%) sildenafil administration. Compared with controls (71.8 ± 3.9 mmHg), hypercontracture was higher (P= 0.0052) after chronic sildenafil administration (89.5 ± 4.1 mmHg), but similar after acute low dose (65.7 ± 3.3 mmHg, P= 0.33) or high dose (67.1 ± 4.7 mmHg, P= 0.43).

Conclusions

The effects of sildenafil after ischaemia/reperfusion were strongly dose-dependent. Beneficial actions on left ventricular function were evident after acute pretreatment with a low dosage, but were lost after doubling the dose. Chronic sildenafil administration deteriorated left ventricular function during ischaemia and reperfusion.

Phosphatidylethanolamine-binding proteins, including RKIP, exhibit affinity for phosphodiesterase-5 inhibitors

Identifying protein "interactors" of drugs is of great importance to understand their mode of action and possible cross-reactivity to off-target protein binders. In this study, we profile proteins that bind to PF-3717842, a high-affinity phosphodiesterase-5 (PDE5) inhibitor, by using a refined affinity pulldown approach with PF-3717842 immobilized beads. By performing these pulldowns in rat testis tissue lysate, we strongly and specifically enriched for PDE5 and a few other PDEs. In addition to these expected affinity-enriched proteins we also detect rodent-specific phosphatidylethanolamine-binding protein 2 (PEBP2), as a putative binder to the PDE5 inhibitor. By using recombinant forms of the related murine mPEBP2, mPEBP1 and human hPEBP1 (also known as Raf kinase inhibitor protein or RKIP) we confirm that they all can bind strongly to immobilized as well as soluble PF-3717842. As the phosphatidylethanolamine-binding proteins are involved in various important signal transduction pathways, the synthetic PDE5 inhibitor used here might form a platform to synthesize enhanced binders/inhibitors of the family of PEBP proteins. Our approach shows how chemical proteomics might be used to profile the biochemical space (interactome) of small molecule inhibitors.

Sildenafil improves scotoma after posterior cerebral infarctions: a case report

A 65-year-old man had an embolic stroke of both posterior cerebral arteries in 2002. Two years later he noted rapid improvement of the residual bilateral inferior quadrant anopia whenever he took 25 mg sildenafil. The improvement of scotomas was verified by visual field examinations and persisted reproducibly for 3-7 days. An overlay of a subtraction of functional magnetic resonance imaging (MRI) during visual stimulation before and after medication onto a T1-weighted MRI of the patient revealed additional activations along the margins of the old cerebral infarctions. These findings and the additional results of a perfusion MRI suggest that phosphodiesterase 5 inhibitors may prove beneficial in the rehabilitative course after ischemic strokes.

Population pharmacokinetic model of the pregabalin-sildenafil interaction in rats: application of simulation to preclinical PK-PD study design

PURPOSE

Preliminary evidence has suggested a synergistic interaction between pregabalin and sildenafil for the treatment of neuropathic pain. The focus of this study was to determine the influence of sildenafil on the pharmacokinetics (PK) of pregabalin with the objective of informing the design of a quantitative pharmacodynamic (PD) study.

METHODS

The pharmacokinetics were determined in rats following 2-hr intravenous infusions of pregabalin at doses of 4 mg/kg/hr and 10 mg/kg/hr with and without a sildenafil bolus (2.2 mg) and steady state infusion (12 mg/kg/hr for 6 h). This PK model was utilized in a preclinical trial simulation with the aim of selecting the optimal sampling strategy to characterize the PK-PD profile in a future study. Eight logistically feasible PK sampling strategies were simulated in NONMEM and examined through trial simulation techniques.

RESULTS

A two-compartment population PK model best described pregabalin pharmacokinetics. Significant model covariates included either a binary effect of sildenafil administration (30.2% decrease in clearance) or a concentration-dependent effect due to sildenafil's active metabolite.

CONCLUSIONS

Analysis of simulations indicated that three post-PD samples had the best cost/benefit ratio by providing a significant increase in the precision (and minor improvement in bias) of both PK and PD parameters compared with no PK sampling.

A systematic review of experimental and clinical studies of sildenafil citrate for intrauterine growth restriction and pre-term labour

Sildenafil could be an alternative in the treatment of intrauterine growth retardation (IUGR) and premature delivery. In order to systematically review the reproductive-related effects of sildenafil, a search was made on PubMed and the Science Citation Index for studies evaluating the effects of sildenafil on uterine vessels or myometrium either in vitro or in experimental animal models as well as for any clinical trial or case reporting the outcome of pregnant women treated with sildenafil. The information was obtained from: three in vitro studies, five studies performed in experimental animal models, four studies on women with fertility and sterility disorders receiving 100 mg/day of sildenafil intravaginally, and two case reports of pregnant women who received sildenafil for the treatment of pulmonary hypertension. Incubation with sildenafil of different in vitro preparations resulted in vasodilator and uterine relaxant effects. No evidence of teratogenicity was observed in the studies performed in mice, rats and dogs. Sildenafil increased fetal weight in rats. In women, contradictory results on uterine blood flow and endometrial development were reported after the intravaginal administration of sildenafil. No adverse fetal outcomes were reported in the two pregnant women with pulmonary hypertension receiving sildenafil late in their pregnancy. In conclusion, there is still limited information about the efficacy of sildenafil for the treatment of IUGR and premature delivery. However, studies in experimental animal models and two human case reports have reported no deleterious effects on the mother or offspring.

Effect of the phosphodiesterase 5 inhibitors sildenafil, tadalafil and vardenafil on rat anococcygeus muscle: functional and biochemical aspects

1. The anococcygeus muscle is part of the erectile machinery in male rodents. Phosphodiesterase (PDE) 5 inhibitors enhance and prolong the effects of cGMP, which has a key role in penile erection. The aim of the present study was to provide a functional and biochemical comparison of the three PDE5 inhibitors, namely sildenafil, tadalafil and vardenafil, in the rat anococcygeus muscle. 2. Muscle strips were mounted in 4 mL organ baths and isometric force recorded. Levels of cGMP were measured using an enzyme immunoassay kit. Western blots were used to determine PDE5 protein expression. 3. The PDE5 inhibitors concentration-dependently relaxed carbachol-precontracted anococcygeus muscle; however, vardenafil was more potent (pEC(50) = 8.11 +/- 0.05) than sildenafil (7.72 +/- 0.06) or tadalafil (7.69 +/- 0.05). Addition of N(G)-nitro-l-arginine methyl ester (100 micromol/L) or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10 micromol/L) to the organ baths caused significant rightward shifts in concentration-response curves for all PDE5 inhibitors. 4. Sildenafil, tadalafil and vardenafil (all at 0.1 micromol/L) caused leftward shifts in the glyceryl trinitrate (GTN) concentration-response curves (by 4.0-, 3.7- and 5.5-fold, respectively). In addition, all three PDE5 inhibitors significantly potentiated relaxation responses to both GTN (0.01-10 micromol/L) and electrical field stimulation (EFS; 1-32 Hz), with vardenafil having more pronounced effects. 5. All three PDE5 inhibitors reduced EFS-evoked contractions in a concentration-dependent manner over the concentration range 0.001-1 micromol/L. There were no significant differences between the effects of the three PDE5 inhibitors. 6. Vardenafil (0.01-0.1 micromol/L) was more potent in preventing cGMP degradation in vitro than sildenafil (0.01-0.1 micromol/L) and tadalafil (0.01-0.1 micromol/L). 7. Under control conditions, the expression of PDE5 was higher in the anococcygeus muscle than in the corpus cavernosum. 8. In conclusion, PDE5 inhibitors enhance exogenous and endogenous nitric oxide-mediated relaxation in the rat anococcygeus muscle. The potency of vardenafil was greater than that of either sildenafil or tadalafil.

Integrating evidence from multiple sources to evaluate post-approval safety: an example of sildenafil citrate and cardiovascular events

OBJECTIVE

Recent high-profile medicine withdrawals have highlighted the complex decision-making process that regulators, pharmaceutical companies, prescribers, and patients must undertake in determining whether a drug has an appropriate benefit-risk balance. Our objective was to analyze the utility of different drug safety data sources and methods, using the experience of sildenafil citrate (Viagra) and post-approval concerns about its potential association with cardiovascular (CV) events (i.e., myocardial infarction [MI] and death) as a case study.

METHODS

We evaluated safety data from three sources: the standard passive surveillance system (i.e., spontaneous reports filed to Pfizer Inc), pooled clinical trial data, and a prospective observational cohort study, the International Men's Health Study (IMHS).

RESULTS

More than 28 000 spontaneous reports were received in the first 7 years after approval. Between 2001 and 2005, the proportion filed by persons other than healthcare professionals (61%) was approximately double the proportion averaged across five other drugs from the manufacturer's safety database. CV events and/or deaths represented 22.0% of reports, and 23% of reported deaths were medically unconfirmed reports made by persons other than healthcare professionals. In contrast, MI and all-cause mortality rates for sildenafil from both the pooled clinical trial data and the IMHS were similar to placebo, despite differences in methods and populations.

CONCLUSIONS

These results suggest that passive surveillance may generate apparent signals of risk, as was the case with sildenafil and CV events. However, to adequately assess the benefit-risk profile of a drug, these signals must be evaluated via other data sources such as clinical trial and epidemiologic studies, as the apparent signal was not supported by more rigorously collected data. Our post-marketing analysis was unable to examine all potential influences of spontaneous reports, and the study data sources (although large for erectile dysfunction studies) were not designed to exclude small CV risks.

Erectile dysfunction medication use among men seeking substance abuse treatment

Few studies of erectile dysfunction (ED) medications use among heterosexual drug using or abusing men have been conducted. The aims of this study were to provide information on ED medication use prevalence, method of acquisition, and sexual effects among men seeking substance abuse treatment. A single time point cross-sectional anonymous survey was completed by 297 men over the age of 18 seeking substance abuse treatment at an outpatient clinic at a Veterans Affairs Medical Center in the Pacific Northwest. Mean age of participants was 49.7 years and 59.4% self-identified as Caucasian. Alcohol (56.7%) and cocaine (26.1%) were the primary drugs of abuse. Lifetime use of ED medications was reported by 24% (95%CI = 8.6%, 39.4%) of men. Almost 69% of ED medication users reported obtaining ED medications from a physician. Fifty-nine percent of ED medication users reported taking the medications to enhance their sexual experience rather than to treat ED, which was marginally associated with stimulant use (OR = 3.86, 95%CI = 0.96, 15.54, p = .057). These results add to an emerging recognition of the need to address the health implications of ED medication use among heterosexual drug using populations.

NO netting, health and stress – Studying wellness from a net perspective

On the nature of wellness, stress, netting and the radical gas nitric oxide (NO). The multi-complex role of NO resulted in its discoverers receiving a Nobel award, its presence everywhere and volatility makes it a suitable candidate to be a main signal in an instantaneous communication network. Such network, with the capacity of tight physiological monitoring, enables assets distributions in the body. A model is presented suggesting that an inter-cellular communication network coordinates the various bodily functions. Radical gases like nitric oxide (NO) are signals in this net and its usability affects health and indicates wellness. From this netting point of view, stress is the sense of flow interruption or blockage of the information stream. Such flow interruption affects also physiological functions and can explain the association between stress and many ailments. It is suggested that netting is a prerequisite route of wellness, enabling bodily unconscious managerial decisions. This vital diffusive network is extremely labile and potentially could contain the interplay of consciousness and unconsciousness effected by activities such as yoga or guided imagery. Vast data from studies on NO signals, health and the relaxation/stress processes have already been accumulated. Integration of these data supports this novel look of an NO network as a coordinator. Interactions between stress and health are discussed in net perspective and include basic concepts of some integrative health approaches. Studying the nature of such communication network and of NO may suggest new ways to reduce stress and approach wellness.

Involvement of alpha-receptors and potassium channels in the mechanism of action of sildenafil citrate

Modulation of the adrenergic activity and interfering with channels such as potassium channels may affect relaxation and contraction of the corpus cavernosum. Sildenafil is a selective phosphodiesterase-5 inhibitor, proven effective in treating erectile dysfunction. In this study, the effect of sildenafil citrate on alpha-receptors modulation and potassium channels was tested. The direct relaxant effect of sildenafil citrate was studied by measuring changes in isometric tension in isolated strips of rabbit corpus cavernosum and rat aortic ring precontracted with phenylephrine or KCl compared to that of diazoxide in the presence and absence of tetraethylammonium. The inhibitory effect of sildenafil on electrical field stimulation-induced contraction of rabbit corpus cavernosum and rat anococcygeus muscle was also studied compared to that of phentolamine. Muscle relaxant effect of sildenafil (1 x 10(-9)-1 x 10(-6) M on phenylephrine-precontracted rabbit corpus cavernosum strips was not attenuated by N(G)-nitro-L-arginine (3 x 10(-5) M). Cumulative addition of sildenafil (1 x 10(-9)-1 x 10(-6) M) and phentolamine (1 x 10(-9)-1 x 10(-6) M) to the organ bath dose-dependently inhibited electrical field stimulation-induced contraction of rabbit corpus cavernosum and rat anococcygeus muscle, with almost similar EC(50) values. Sildenafil (1 x 10(-7) M) also inhibited phenylephrine-induced contraction of rat aortic rings by 39.83+/-3.01%. In addition, tetraethylammonium (1 x 10(-3) M) significantly attenuated the muscle relaxant effect of sildenafil (1 x 10(-9)-1 x 10(-6) M) on phenylephrine-precontracted strips of rabbit corpus cavernosum. Sildenafil citrate is capable of producing cavernosal smooth muscle relaxation by an additional mechanism that may involve alpha-receptors and potassium channel opening.

Factors that predict changing the type of phosphodiesterase type 5 inhibitor medication among men in the UK

OBJECTIVE

To evaluate predictors of changing the type of phosphodiesterase type 5 (PDE5) inhibitor (switching) among men with erectile dysfunction (ED) in the UK, the largest consumer of PDE5 inhibitors in Europe, as switching medication is often associated with higher resource use, and there are three oral PDE5 inhibitor medications currently available.

PATIENTS AND METHODS

Patients were identified from The Health Improvement Network database in the UK; men initiating therapy with sildenafil, tadalafil or vardenafil from May 2003 to August 2004 with >/= 6 months of prescription history before and after their initial PDE5 inhibitor prescription were included. Switching was evaluated as the proportion of second PDE5 inhibitor prescriptions that were for a drug differing from the first. Logistic regression was used to adjust for factors that might be associated with switching (dose, age and the presence of hypertension, dyslipidaemia, diabetes or depression).

RESULTS

Of the 2703 eligible men who initiated PDE5 inhibitor treatment during the study period, 91 (3.4%) switched to a different PDE5 inhibitor at their second prescription. The choice of initial PDE5 inhibitor therapy was a highly significant predictor of switching; men initiated on sildenafil were less likely to switch than those initiated on tadalafil (P < 0.001) or vardenafil (P < 0.003). Age and the presence of comorbidities were not significantly associated with switching (P > 0.05).

CONCLUSION

Initiating ED therapy with sildenafil was associated with the lowest rate of PDE5 inhibitor switching, which might reflect treatment satisfaction and patient preference.

Nitrate Cessation Profiles in Men Wishing to Use Sildenafil Citrate

OBJECTIVES

To define the likelihood of nitrate users wishing to use sildenafil citrate being permitted by their nitrate-prescribing physicians to cease nitrate use, and to attempt to derive predictors of a "no" response to this request.

METHODS

A total of 248 patients with erectile dysfunction were included in this study. All patients using or in possession of nitrates who opted to be treated with sildenafil had letters sent to the nitrate-prescribing physician, asking whether the nitrate could be ceased so as to facilitate sildenafil use.

RESULTS

Of 248 letters, 236 (95.7%) were answered by the nitrate-prescribing physicians. The types of nitrate use included oral (72 patients), sublingual (150 patients), and transdermal (14 patients); mean patient age was 64 years. To the question, "Would you permit the patient to cease use or possession of nitrate, to facilitate the use of sildenafil," 42% of the physicians (99 of 236) responded "yes." For men who were using oral, transdermal, and as-required sublingual nitrates, 28%, 0, and 53% of letters had a "yes" response. In a multivariable analysis we found five predictors of a "no" response: patient age greater than 65 years, duration of nitrate possession less than 6 months, oral/transdermal nitrate use, sublingual nitrate use more than once per year, and nitrate medication prescribed by a non-cardiology physician.

CONCLUSIONS

We demonstrated that 42% of men with erectile dysfunction who were using nitrates were permitted to discard their nitrates to facilitate sildenafil use, and we identified factors predicting a "no" response to such a request.

Assessment of heme oxygenase-1 (HO-1) activity in the cavernous tissues of sildenafil citrate-treated rats

AIM

To assess heme oxygenase-1 (HO-1) activity in the cavernous tissue of sildenafil citrate-treated rats.

METHODS

One hundred and ninety-two Sprague-Dawley male rats, divided into four equal groups, were investigated. Group 1, the control group, received regular animal chow; group 2 received sildenafil citrate by intragastric tube; group 3 received sildenafil and HO inhibitor (zinc protoporphyrin, ZnPP); and group 4 received sildenafil and nitric oxide synthase (NOS) inhibitor L-nitroarginine methyl ester (L-NAME). Twelve rats from each group were killed after 0.5 h, 1 h, 2 h and 3 h of drug administration. Then HO-1 activity, cGMP levels and NOS enzymatic activity in the cavernous tissues were estimated.

RESULTS

In cavernous tissue, HO-1 activity, NOS enzymatic activity and cGMP concentration increased significantly in sildenafil-treated rats compared to other groups throughout the experiment. Rats receiving either HO or NOS inhibitors showed a significant decrease in these parameters. HO-1 cavernous tissue activity and NOS enzymatic activity demonstrated a positive significant correlation with cGMP levels (r = 0.646, r = 0.612 respectively; P < 0.001).

CONCLUSION

The actions of PDE5 inhibitor sildenafil citrate in the cavernous tissue are partly mediated through the interdependent relationship between both HO-1 and NOS activities.

The role of nitric oxide in erectile dysfunction: implications for medical therapy

Erectile dysfunction is a common, multifactorial disorder that is associated with aging and a range of organic and psychogenic conditions, including hypertension, hypercholesterolemia, diabetes mellitus, cardiovascular disease, and depression. Penile erection is a complex process involving psychogenic and hormonal input, and a neurovascular nonadrenergic, noncholinergic mechanism. Nitric oxide (NO) is believed to be the main vasoactive nonadrenergic, noncholinergic neurotransmitter and chemical mediator of penile erection. Released by nerve and endothelial cells in the corpora cavernosa of the penis, NO activates soluble guanylyl cyclase, which increases 3',5'-cyclic guanosine monophosphate (cGMP) levels. Acting as a second messenger molecule, cGMP regulates the activity of calcium channels as well as intracellular contractile proteins that affect the relaxation of corpus cavernosum smooth muscle. Impaired NO bioactivity is a major pathogenic mechanism of erectile dysfunction. Treatment of erectile dysfunction often requires combinations of psychogenic and medical therapies, many of which have been only moderately successful in the past. The advent of oral phosphodiesterase type 5 (PDE-5) inhibitors, however, has greatly enhanced erectile dysfunction treatment; patients have demonstrated high tolerability and success rates for improved erectile function. The efficacy of the PDE-5 inhibitors also serves to illustrate the importance of the NO-cGMP pathway in erectile function since these agents counteract the degradation of NO-generated cGMP. Because not all patients respond to PDE-5 inhibitors, additional therapies are being investigated, such as soluble guanylyl cyclase activators and NO donors, which act on NO-independent and NO-dependent pathways, respectively.

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.