Phosphodiesterase type 5 inhibitors: the day after

Erectile dysfunction and lower urinary tract

During the last decades it turned out that the NO/cGMP signaling cascade is one of the most prominent regulators of a variety of physiological and pathophysiological processes in a broad range of mammalian tissues. Thus cGMP is a key second messenger and targeting this pathway by increasing intracellular cGMP levels is a very successful approach in pharmacology as shown for nitrates, PDE5 inhibitors and more recently for stimulators of the guanylate cyclase. Besides the beneficial effects of cGMP elevation in cardiac, vascular, pulmonary, renal or liver disorders the launch of PDE5 inhibitors for the treatment of erectile dysfunction 10 years ago, has directed a lot of attention to the NO/cGMP signaling in the lower urinary tract. Triggered by the use of PDE5 inhibitors in ED it turned out that cGMP is a common regulatory mechanism for lower urinary tract function also beyond ED. In recent years intense research and development efforts were undertaken to elucidate the role of the NO/cGMP and to fully exploit the therapeutic implications of cGMP elevation in urological disorders in ED and beyond. Therefore we have summarized the effects of cGMP elevation for treatment of erectile dysfunction in males and in females. We have also reviewed the recent pre-clinical and clinical lines of evidence for treatment options of benign prostatic hyperplasia and lower urinary tract symptoms in male patients and overactive bladder and urinary incontinence in female patients. In addition we also touch more speculative concepts using cGMP elevating drugs for the treatment of premature ejaculation, peyornies disease and stone disease.

The use of phosphodiesterase 5 inhibitors with concomitant medications

The phosphodiesterase-5 inhibitors (PDE5i) sildenafil, vardenafil, and tadalafil are considered first-line therapy for the treatment of patients with erectile dysfunction (ED). In addition to the classical pro-erectile-effect, clinical findings have suggested that they can also influence vascular tone in pulmonary, coronary and other vascular tissues, as well as improving symptoms associated with benign prostatic hyperplasia. Therefore, considering the hypothetical widespread application of PDE5i, the potential for drug-drug interactions emerges as a relevant factor in determining the safety profile of PDE5i. Review of relevant literature was conducted using data sources from MEDLINE (1998, to June 2007). The use of nitrates remains the only contraindication for all 3 PDE5i. Vardenafil is also not recommended in patients taking type 1A (such as quinidine, or procainamide) or type 3 antiarrhythmics (such as sotalol, or amiodarone) while no other major limitations have been reported for tadalafil and sildenafil. In contrast to previously reported labeling, recent studies have suggested only a precaution, but not contraindication with the concomitant use of alpha-blockers agents. In addition, precaution is also suggested in the presence of potent CYP3A inhibitors, such as azole antifungals, antiretroviral protease inhibitors, or macrolid antibiotics. This is because sildenafil, vardenafil, and tadalafil are metabolized mainly via the CYP3A4 pathway. On the other hand, statins and testosterone seem to have synergic effects with PDE5i on sexual activity.

Efficacy of tadalafil once daily in men with diabetes mellitus and erectile dysfunction

AIMS

Erectile dysfunction (ED) is a common comorbidity in men with diabetes mellitus. Tadalafil 10 or 20 mg taken on demand is efficacious and safe for men with diabetes and ED. Recently, continuous treatment with tadalafil has been proposed, addressing ED management as any other chronic condition. This study examined whether once-daily tadalafil 2.5 and 5 mg is efficacious for men with diabetes and ED.

METHODS

This randomized, double-blind, placebo-controlled, multicentre, 12-week study enrolled 298 men with diabetes and ED to once-daily treatment with placebo, tadalafil 2.5 mg or tadalafil 5 mg. Primary efficacy measures were International Index of Erectile Function Erectile Function (IIEF EF) Domain score, and patient success rates for vaginal penetration and completion of intercourse. Patient satisfaction, endothelial function biomarkers, and safety were also assessed.

RESULTS

Patients receiving either dose of tadalafil had clinically and statistically significant improvements in IIEF EF and statistically significant improvements in mean success rates for vaginal penetration, completion of intercourse, and overall treatment satisfaction (P < or = 0.005 tadalafil vs. placebo, all measures). Endothelial dysfunction biomarkers were unchanged. The most common adverse events were headache, back pain and dyspepsia.

CONCLUSIONS

In this first study of men with diabetes and ED, once-daily tadalafil 2.5 and 5 mg was efficacious and well tolerated, suggesting this may be an alternative to on-demand treatment for some men, eliminating the need to plan sex within a limited timeframe.

Centrally acting mechanisms for the treatment of male sexual dysfunction

The development of pharmacologic therapy for erectile dysfunction (ED) has been possible because of incremental growth in our understanding of the physiology of normal erections and the complex pathophysiology of ED. Although the oral phosphodiesterase type 5 (PDE5) inhibitors have provided safe, effective treatment of ED for some men, a large proportion of men who have ED do not respond to PDE5 inhibitors or become less responsive or less satisfied as the duration of therapy increases. Also, men who are receiving organic nitrates and nitrates, such as amyl nitrate, cannot take PDE5 inhibitors because of nitrate interactions. The current options for treatment beyond PDE5 inhibitors are invasive, unappealing to some patients, and sometimes ineffective. The search for other options by which ED can be treated has branched out and now encompasses centrally acting mechanisms that control erectile function. Drugs available in Europe include apomorphine. This article focuses on the mechanism of centrally acting agents and reviews clinical data on potential new centrally acting drugs for men who have ED.

Antioxidant Treatment Associated with Sildenafil Reduces Monocyte Activation and Markers of Endothelial Damage in Patients with Diabetic Erectile Dysfunction: A Double-Blind, Placebo-Controlled Study

OBJECTIVE

To investigate the synergic effect of propionyl L-carnitine (PLC) plus sildenafil in reducing monocyte oxidative activity and endothelial dysfunction markers in diabetic patients with erectile dysfunction (ED).

METHODS

Thirty-two type 2 diabetic patients with ED (according to the International Index of Erectile Function-5 [IIEF-5]) were randomized to receive PLC (2 g/d) alone (n=8) or combined with sildenafil (50 mg/d twice weekly) (n=8), sildenafil alone (50 mg/d twice weekly) (n=8), or placebo (n=8) in a double-blind, fixed-dose study. Monocyte oxidative activity (stimulation index [SI]), intercellular adhesion molecule-1 [ICAM-1], P-selectin, advanced glycation end product (AGE) levels, Doppler sonography (recording peak systolic velocity [PSV]; end diastolic velocity [EDV]; systolic wave time [SWT]; resistive index [RI]), and IIEF score were evaluated before and after 12 wk of treatment; IIEF-5 was evaluated again 4 wk posttreatment.

RESULTS

SI was reduced by treatment with PLC alone or combined with sildenafil (p<0.05). In patients treated with PLC plus sildenafil, a decrease in ICAM-1, P-selectin, and EDV values was observed compared with patients treated with sildenafil alone (p<0.05, p<0.01, p<0.001, respectively). IIEF-5 improved in all patients treated with PLC plus sildenafil or sildenafil alone (p<0.03, p<0.05, respectively). Four weeks posttreatment, patients treated with PLC plus sildenafil maintained the improvement of the IIEF-5 compared with patients on sildenafil alone (p=0.05). In patients on PLC treatment (with or without sildenafil), SI was correlated with IIEF-5 (p<0.001), glycemia with STW (p<0.03), and AGEs with IIEF-5 (p<0.01).

CONCLUSION

PLC plus sildenafil was more effective in reducing SI and endothelial dysfunction markers in patients with type 2 diabetes and ED.

Daily treatment with sildenafil reverses endothelial dysfunction and oxidative stress in an animal model of insulin resistance

OBJECTIVES

Patients with insulin resistance exhibit endothelial dysfunction with decreased nitric oxide (NO) production and increased oxidative stress. We postulated that daily sildenafil improved endothelial function in fructose-fed rats.

METHODS AND RESULTS

Wistar rats were fed a standard or fructose-enriched diet (FFR) for 9 wk. From weeks 6-8, sildenafil was administered twice daily (sc, 20 m g/kg), followed by a 1-wk washout. Concentration-response curves (CRCs) to endothelium-dependent (acetylcholine [Ach] and A23187) and -independent (sodium nitroprusside [SNP]) relaxing agents were performed on isolated precontracted aortas and superior mesenteric arteries (SMAs). Vascular cyclic guanosine monophosphate (cGMP) content, urinary excretion of nitrates/nitrites (NOx) and 8-isoprostanes (IPT), and plasma levels of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) were evaluated. Relaxations to ACh were significantly reduced in aortas and SMAs of FFR. Sildenafil restored ACh-induced relaxations in aortas and provoked a significant leftward shift of the CRC to ACh in SMAs, whereas it did not modify the enhanced relaxations to SNP in FFR. IL-6, TNF-alpha, vascular cGMP, and urinary NOx levels were not modified by the fructose or sildenafil treatment. Urinary IPT levels were significantly elevated in FFR and normalized by sildenafil.

CONCLUSIONS

Endothelial dysfunction and oxidative stress associated with insulin resistance can be reversed by daily sildenafil, even 1 wk after treatment cessation.

Erectile dysfunction drugs and risk of anterior ischaemic optic neuropathy: casual or causal association?

Phosphodiesterase type 5 (PDE5) inhibitor drugs for erectile dysfunction have revolutionised the treatment of male sexual dysfunction and are among the best selling drugs worldwide. Several cases of non-arteritic anterior ischaemic optic neuropathy (NAION) have been reported since 2005 in users of these agents. NAION is a sudden irreversible cause of visual loss with a poorly understood aetiology that affects up to 10 adults per 100,000 each year. Following a series of such case reports, WHO and FDA have labelled the association between use of PDE5 inhibitors and risk of NAION as "possibly" causal. There have been several recent studies of this association, including a rechallenge case report and a large managed care database study. However, the inability to confirm or refute claims of an association between NAION and EDD is generating clinical and regulatory uncertainty. Questions surrounding use of PDE5 inhibitors and risk of NAION highlight weaknesses in current systems used to identify and evaluate uncommon adverse effects of medication use. This paper reviews all the recent evidence on PDE5 inhibitors and the risk of NAION.

The Role of Phosphodiesterase Type 5 Inhibitors in the Management of Premature Ejaculation: A Critical Analysis of Basic Science and Clinical Data

OBJECTIVES

To assess the usefulness of the phosphodiesterase type 5 inhibitors (PDE5-Is) in the treatment of premature ejaculation (PE) and to describe possible mechanisms to explain their effect.

METHODS

A MedLine search was performed for peer-reviewed articles on the role of PDE5-Is in managing PE. No meta-analysis method was used.

RESULTS

Five manuscripts that examined the efficacy of PDE5-Is in the treatment of PE were retrieved. Three studies used sildenafil as monotherapy and two used it in combination with a serotonin selective reuptake inhibitor (SSRI). Three studies demonstrated a beneficial effect of sildenafil in the treatment of PE, as measured by intravaginal ejaculatory latency time (IELT) and by different questionnaires assessing the patients' subjective feelings of ejaculatory control, sexual satisfaction, and anxiety. One study showed the superiority of sildenafil compared to other modalities. Two studies showed that combination therapy of paroxetine and sildenafil was better than paroxetine alone. One study did not demonstrate a beneficial effect of sildenafil in prolonging IELT, but showed that sildenafil improved patients' perception of ejaculatory control. Another study showed that topical anesthetics were better than sildenafil in the treatment of PE but did not use IELT or a validated questionnaire to measure the efficacy of treatment. Several possible mechanisms could explain effectiveness of the PDE5-Is for treatment of PE: centrally, through the effect on the nitric oxide/cyclic guanosine monophosphate pathway; peripherally by causing relaxation of smooth muscle in the vas deferens, seminal vesicles, prostate, and urethra and inhibition of adrenergic transmission; or locally by inducing peripheral analgesia. Another possibility might be prolongation of the duration of erection.

CONCLUSIONS

Encouraging evidence supports the role of PDE5-Is for treating PE. Possible therapeutic mechanisms of action of PDE5-Is are multiple and complex and include central and peripheral effects. A large population, multicenter, randomized, double-blind, placebo-controlled study is needed to elucidate the efficacy of PDE5-Is in the treatment of PE.

Patterns of switching phosphodiesterase type 5 inhibitors in the treatment of erectile dysfunction: results from the Erectile Dysfunction Observational Study

AIMS

This report describes patterns of treatment changes with the phosphodiesterase type 5 (PDE5) inhibitors tadalafil, sildenafil and vardenafil, and variables associated with those treatment changes, during the 6-month, prospective, pan-European Erectile Dysfunction Observational Study (EDOS).

METHODS

EDOS observed 8047 men > or = 18 years old with erectile dysfunction (ED), who began or changed ED therapy as part of their routine healthcare. Patients could change ED treatment at any time during EDOS. Data were collected at baseline and at 3 (+/- 1) and 6 (+/- 1) months. Analyses included ED treatment-naïve patients with complete follow-up who were prescribed a PDE5 inhibitor at baseline (n = 4026).

RESULTS

Most patients, regardless of what PDE5 inhibitor they were prescribed at baseline, continued on that same PDE5 inhibitor throughout the study. Continuation rates were approximately 89% in the tadalafil cohort, vs. 63-64% in the sildenafil and vardenafil cohorts. The variables most strongly associated with increased risk of switching were prescription of sildenafil or vardenafil, vs. tadalafil, at baseline (odds ratios 4.43 and 4.14 respectively; p < 0.0001). Of patients who switched from tadalafil to another treatment, nearly 25% had switched back to tadalafil by study end. In contrast, of patients who switched from sildenafil or vardenafil, < 10% from each cohort had switched back to their original treatment by study end.

CONCLUSION

The data suggest that tadalafil treatment in treatment-naïve ED patients may increase their likelihood of treatment continuation. These findings should be interpreted conservatively due to the observational nature of the study.

Daily Administration of Phosphodiesterase Type 5 Inhibitors for Urological and Nonurological Indications

OBJECTIVES

Although the discovery of phosphodiesterases (PDEs) was made soon after the identification of cyclic adenosine monophosphate nearly half a century ago, their true importance in medicine has taken many decades to be realised. The recognition of the important role PDE enzymes play and the impact of altering intracellular cyclic nucleotide levels became significant for most urologists and clinicians in the early 1990s with the discovery of sildenafil, a PDE5 inhibitor (PDE5-I). Once approved around the world, on-demand use of PDE5-Is became the gold standard. Recently, the potential beneficial effects of PDE5-Is on the pulmonary, vascular, and other systems has led to examination of alternative dosing regimens. In this review, we have synthesised the available published peer-reviewed literature to provide a critical contemporary view of evolving indications for PDE5-Is and how alternative dosing regimens may impact on sexual and other functions.

METHODS

MEDLINE search of all peer-reviewed English literature for the period 1990-2007.

RESULTS

The plethora of articles detailing potential uses of PDE5-I in multiple fields of medicine was uncovered. Use of alternative dosing regimens shows great promise across a number of clinical indications, including post-radical retropubic prostatectomy, pulmonary hypertension, endothelial dysfunction, and salvage of on-demand PDE5-I nonresponders.

CONCLUSIONS

Use of PDE5-I on a daily basis may evolve into a major form of drug administration both for men with erectile dysfunction and for those with a myriad of other conditions shown to benefit from this approach.

Immunohistochemical distribution of cyclic GMP-dependent protein kinase-1 in human prostate tissue

OBJECTIVES

Phosphodiesterase 5 (PDE5) inhibitors improve smooth muscle relaxation and therefore are considered for pharmacotherapy of benign prostatic hyperplasia (BPH) and lower urinary tract symptoms (LUTS). Cyclic guanosine monophosphate (cGMP)-dependent protein kinase-1 (cGKI) has been identified as one of the downstream targets for cGMP. The aim of the present study was to evaluate, by means of immunohistochemistry and Western blot analysis, the expression and localization of cGKI isoforms in relation to smooth muscle alpha-actin and cGMP in the human prostate.

METHODS

Cryostat sections of tissue segments excised from the transition zone of human prostates from 11 patients (aged 54-68 yr) were incubated with primary antibodies directed against smooth muscle alpha-actin, cGMP, cGKI, cGKIalpha, and cGKIbeta. Visualization of double-labelled immunofluorescent staining was achieved by laser microscopy. Western blot analysis was performed to confirm the expression of cGKI isoforms.

RESULTS

Immunoreactivities specific for cGKI, cGKIalpha, and cGKIbeta were observed in the smooth musculature of the transition zone. Double-staining revealed the colocalization of smooth muscle alpha-actin, cGMP, and cGKI isoforms in smooth muscle cells of the fibromuscular stroma. The expression of cGKI isoforms was confirmed by Western blot analysis.

CONCLUSIONS

Our results confirm the presence of cGKI isoforms alpha and beta in the transition zone of human prostate tissue. In addition, the colocalization of alpha-actin, cGMP, and cGKI isoforms provides further evidence for a significant role of the nitric oxide/cGMP pathway in the regulation of smooth muscle contractility in human prostate tissue and therefore could provide additional targets for pharmacotherapy of BPH and LUTS.