Efficacy of Sildenafil as a Rescue Therapy for Patients With Severe Pulmonary Arterial Hypertension and Given Long-term Treatment With Prostanoids: 2-Year Experience

Strategies for optimizing intravenous prostacyclin-analog therapy in patients with pulmonary arterial hypertension

INTRODUCTION

Intravenous prostacyclin-analogs (PCA, e.g. epoprostenol, treprostinil, iloprost) have become an essential part in the therapy of patients with pulmonary hypertension (PH), mainly pulmonary arterial hypertension (PAH). They show considerable differences in pharmacology. A combination therapy including intravenous drugs is regarded as the 'gold standard' in most of PAH patients.

AREAS COVERED

This review discusses and summarizes the studies and concepts on which this therapy is based. To date, intravenous prostacyclin-analogs are mainly administered when standard therapy fails to improve patients to low-risk status. However, preliminary data from uncontrolled studies suggest that an 'upfront triple' therapy including intravenous or subcutaneous prostacyclin-analogs could be preferable in selected patients.

EXPERT OPINION

Various IV PCA have been evaluated in the treatment of patients with PAH. Today, combination therapy is the 'gold standard' for the majority of patients. Intravenous PCA is recommended from functional class III onwards. Timing of its initiation is still a point of discussion. An escalation of therapy to IV or SC PCA is always necessary if a low-risk status cannot be achieved with other targeted therapies. Preliminary data suggest that selected patients could benefit from an 'upfront triple' therapy. Controlled studies on which such recommendation could be based are lacking.

Echocardiography in Pulmonary Arterial Hypertension: Is It Time to Reconsider Its Prognostic Utility?

Pulmonary arterial hypertension (PAH) is characterized by an insult in the pulmonary vasculature, with subsequent right ventricular (RV) adaptation to the increased afterload that ultimately leads to RV failure. The awareness of the importance of RV function in PAH has increased considerably because right heart failure is the predominant cause of death in PAH patients. Given its wide availability and reduced cost, echocardiography is of paramount importance in the evaluation of the right heart in PAH. Several echocardiographic parameters have been shown to have prognostic implications in PAH; however, the role of echocardiography in the risk assessment of the PAH patient is limited under the current guidelines. This review discusses the echocardiographic evaluation of the RV in PAH and during therapy, and its prognostic implications, as well as the potential significant role of repeated echocardiographic assessment in the follow-up of patients with PAH.

Combination Therapy in Pulmonary Arterial Hypertension-Targeting the Nitric Oxide and Prostacyclin Pathways

Pulmonary arterial hypertension (PAH) is a chronic and progressive disorder characterized by vascular remodeling of the small pulmonary arteries, resulting in elevated pulmonary vascular resistance and ultimately, right ventricular failure. Expanded understanding of PAH pathophysiology as it pertains to the nitric oxide (NO), prostacyclin (prostaglandin I₂) (PGI₂) and endothelin-1 pathways has led to recent advancements in targeted drug development and substantial improvements in morbidity and mortality. There are currently several classes of drugs available to target these pathways including phosphodiesterase-5 inhibitors (PDE5i), soluble guanylate cyclase (sGC) stimulators, prostacyclin class agents and endothelin receptor antagonists (ERAs). Combination therapy in PAH, either upfront or sequentially, has become a widely adopted treatment strategy, allowing for simultaneous targeting of more than one of these signaling pathways implicated in disease progression. Much of the current treatment landscape has focused on initial combination therapy with ambrisentan and tadalafil, an ERA and PDE5I respectively, following results of the AMBITION study demonstrating combination to be superior to either agent alone as upfront therapy. Consequently, clinicians often consider combination therapy with other drugs and drug classes, as deemed clinically appropriate, for patients with PAH. An alternative regimen that targets the NO and PGI₂ pathways has been adopted by some clinicians as an effective and sometimes preferred therapeutic combination for PAH. Although there is a paucity of prospective data, preclinical data and results from secondary data analysis of clinical studies targeting these pathways may provide novel insights into this alternative combination as a reasonable, and sometimes preferred, alternative approach to combination therapy in PAH. This review of preclinical and clinical data will discuss the current understanding of combination therapy that simultaneously targets the NO and PGI₂ signaling pathways, highlighting the clinical advantages and theoretical biochemical interplay of these agents.

Intravenous prostacyclin-analogue therapy in pulmonary arterial hypertension - A review of the past, present and future

Therapy with intravenous prostacyclin analogues in patients with pulmonary arterial hypertension (PAH) has been established for decades and is an integral component of the current guidelines for the treatment of pulmonary hypertension. Initially, these drugs were infused by external pump systems via tunnelled right atrial catheters with the need for cooling and frequent exchange of drug reservoirs. Associated complications included, among others, catheter-related infections. More recently, fully implantable pump systems have been developed with drug reservoirs that are filled transcutaneously, allowing intervals between refills of several weeks. This technique results in a low rate of infections. Epoprostenol, iloprost and treprostinil have all been used intravenously in PAH, but titration, dosing and dose escalation in long-term therapy are not standardized. Intravenous prostacyclin analogues are still under-used, despite available data suggesting that early and broad application of these therapies as part of risk-oriented, guideline-directed combination therapy for patients with PAH may lead to a survival benefit. This review provides a detailed overview of the drugs, infusion systems and dosing strategies used for intravenous therapy in patients with PAH.

Network meta-analysis combining individual patient and aggregate data from a mixture of study designs with an application to pulmonary arterial hypertension

Background

Network meta-analysis (NMA) is a methodology for indirectly comparing, and strengthening direct comparisons of two or more treatments for the management of disease by combining evidence from multiple studies. It is sometimes not possible to perform treatment comparisons as evidence networks restricted to randomized controlled trials (RCTs) may be disconnected. We propose a Bayesian NMA model that allows to include single-arm, before-and-after, observational studies to complete these disconnected networks. We illustrate the method with an indirect comparison of treatments for pulmonary arterial hypertension (PAH).

Methods

Our method uses a random effects model for placebo improvements to include single-arm observational studies into a general NMA. Building on recent research for binary outcomes, we develop a covariate-adjusted continuous-outcome NMA model that combines individual patient data (IPD) and aggregate data from two-arm RCTs with the single-arm observational studies. We apply this model to a complex comparison of therapies for PAH combining IPD from a phase-III RCT of imatinib as add-on therapy for PAH and aggregate data from RCTs and single-arm observational studies, both identified by a systematic review.

Results

Through the inclusion of observational studies, our method allowed the comparison of imatinib as add-on therapy for PAH with other treatments. This comparison had not been previously possible due to the limited RCT evidence available. However, the credible intervals of our posterior estimates were wide so the overall results were inconclusive. The comparison should be treated as exploratory and should not be used to guide clinical practice.

Conclusions

Our method for the inclusion of single-arm observational studies allows the performance of indirect comparisons that had previously not been possible due to incomplete networks composed solely of available RCTs. We also built on many recent innovations to enable researchers to use both aggregate data and IPD. This method could be used in similar situations where treatment comparisons have not been possible due to restrictions to RCT evidence and where a mixture of aggregate data and IPD are available.

Electronic supplementary material

The online version of this article (doi:10.1186/s12874-015-0007-0) contains supplementary material, which is available to authorized users.

Clinical utility of treprostinil in the treatment of pulmonary arterial hypertension: an evidence-based review

Pulmonary arterial hypertension (PAH) remains a progressive disease without a cure, despite the development of several treatment options over the past several decades. Its management strategy consists of the endothelin receptor antagonists (ambrisentan, bosentan, macitentan), phosphodiesterase-5 inhibitors (sildenafil, tadalafil, vardenafil), and prostacyclin analogs (epoprostenol, treprostinil, iloprost). Treprostinil, a stable prostacyclin analog, displays vasodilatory effects in the pulmonary vasculature, as well as antiplatelet aggregation properties. Clinical practice guidelines recommend oral endothelin receptor antagonist or phosphodiesterase inhibitor therapy in mild to moderate PAH. Epoprostenol is specifically suggested as first-line therapy in moderate to severe PAH patients (ie, World Health Organization/New York Heart Association functional class III-IV). However, treprostinil may be an alternative option in these severe PAH patients. The longer half-life and stability at room temperature with treprostinil may be associated with lower risk of pulmonary hemodynamic worsening as a result of abrupt infusion discontinuation and less frequent drug preparation. These characteristics make treprostinil an attractive alternative to continuous infusion of epoprostenol, due to convenience and patient safety. The purpose of this review is to evaluate the safety and efficacy of continuous infusion of treprostinil as well as the inhaled and oral routes of administration in PAH.

Assessment of right ventricular responses to therapy in pulmonary hypertension

Irrespective of its cause, pulmonary hypertension (PH) leads to an increase in pulmonary vascular resistance (PVR). Failing adaption of the right ventricle (RV) to the increased afterload is the main cause of death in PH patients and therefore monitoring RV function during treatment is essential. However, consensus on the optimal method for serial assessment of RV function is lacking and therefore the major clinical trials on PH-specific therapies have not provided clear answers with respect to the response of the RV to treatment. This short review will give an overview of the most important load-dependent and load-independent parameters for assessing RV response to therapy in PH patients.

Long-term sildenafil added to intravenous epoprostenol in patients with pulmonary arterial hypertension

BACKGROUND

In pulmonary arterial hypertension (PAH), adding oral sildenafil to intravenous epoprostenol improved 6-minute walk distance (6MWD) and hemodynamics and delayed time to clinical worsening in a 16-week randomized, placebo-controlled trial (Pulmonary Arterial Hypertension Combination Study of Epoprostenol and Sildenafil [PACES-1]).

METHODS

Patients completing PACES-1 could receive sildenafil (titrated to 80 mg, three times daily, as tolerated) in an open-label extension study (PACES-2) for ≥ 3 years; additional therapy was added according to investigator judgment. Survival and changes from PACES-1 baseline in World Health Organization Functional Class and 6MWD were captured.

RESULTS

In an open-label setting, 6MWD, an effort-dependent outcome measure, was known to have improved or to have been maintained in 59%, 44%, and 33% of patients at 1, 2, and 3 years, respectively; functional class was known to have improved or to have been maintained in 73%, 59%, and 46%. At 3 years, 66% of patients were known to be alive, 24% were known to have died, and 10% were lost to follow-up. Patients with PACES-1 baseline 6MWD < 325 meters without 6MWD improvement during the first 20 weeks of sildenafil treatment subsequently had poorer survival.

CONCLUSIONS

Although reliable assessments of safety and efficacy require a long-term randomized trial, the addition of sildenafil to background intravenous epoprostenol therapy appeared generally to be well tolerated in PAH patients.

Combination therapy in pulmonary arterial hypertension

Despite major advances in understanding the mechanisms of disease and development of specific drug therapy, pulmonary arterial hypertension (PAH) remains a progressive, fatal disease. At present there are 3 classes of drug therapy for PAH: prostaglandins, endothelin receptor antagonists, and phosphodiesterase-5 inhibitors. To maximize therapeutic benefit, and according to national and international guidelines, many patients are treated with combinations of these medications. This review presents a detailed account of the published data on the use of combination therapy in PAH. There are few randomized, placebo-controlled trial data to strongly support efficacy of most combination therapy, particularly oral combination therapy.

Combination therapy in pulmonary arterial hypertension

Many potential therapeutic options are now available for patients with pulmonary arterial hypertension. Interest has emerged in using therapies in various combinations. Retrospective experience has suggested that this approach is common and can be efficacious. Data are emerging supporting the benefit of combination therapy; however, limitations and questions remain about this strategy. This report reviewed the rationale for combination therapy and summarized the results from clinical trials.

Pulmonary arterial hypertension: new insights into the optimal role of current and emerging prostacyclin therapies

Pulmonary arterial hypertension (PAH), which is a subset of pulmonary hypertension, is a group of diseases distinguished by vascular remodeling of the small pulmonary arteries with associated elevated pulmonary arterial pressure and right ventricular failure. This progressive and sometimes fatal disease occurs as an idiopathic disease or as a component of other disease states. Estimates of the incidence of PAH have varied from 5 to 52 cases/1 million population. Symptoms begin with shortness of breath with exertion and progress to dyspnea with normal activities and, finally, dyspnea at rest. Untreated patients with PAH have a 1-, 3-, and 5-year survival rate of 68%, 48%, and 34%, respectively. Treated, the survival rates improve to 91% to 97% after 1 year and 84% to 91% after 2 years. The current definition of PAH consists of 3 specific hemodynamic assessments confirmed by right heart catheterization findings. One of several important pathophysiologic mechanisms involved in PAH is pulmonary vascular remodeling, which is caused by endothelial and smooth muscle cell hyperproliferation. This is coincident with overexpression of the vasoconstrictor endothelin-1 and a reduction in the vasodilators nitric oxide and prostacyclin, which further impedes proper vasomotor tone, among other effects. Prostacyclin therapies augment the decreased prostacyclin levels in patients with PAH. The currently approved prostacyclins for the treatment of PAH include epoprostenol, iloprost, and treprostinil. Among the 3 medications, the delivery options include intravenous infusion, subcutaneous infusion, and inhaled formulations. Epoprostenol has been shown to have a positive effect on survival in patients with PAH. All prostacyclins have demonstrated improvements in functional class, exercise tolerance, and hemodynamics in patients with PAH. Intravenously and subcutaneously administered formulations of prostacyclins require continuous infusion pump administration, which presents clinical challenges for both the patient and the care provider. Dosing must be individualized and also presents a clinical challenge. Inhaled formulations seem efficacious in moderately symptomatic patients with PAH and might be appropriate when combined with an oral medication. Combination therapies are commonly used in clinical practice, with the decision to do so based on randomized controlled trial data and case study evidence. The present report provides an overview of PAH, the scientific rationale for treatment with prostacyclin therapy, and the benefits and risks of prostacyclin therapy, both as monotherapy and combined with other medications approved for the treatment of PAH.

Combination Pharmacotherapy in the Treatment of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a disorder of the small pulmonary arteries characterized by progressive fibrotic and proliferative changes that result in an increased pulmonary vascular resistance. It is a progressive and debilitating disease that leads to right ventricular dysfunction, impairment in activity tolerance and eventually right-sided heart failure, and premature death. The treatment goals for PAH include improvement in symptoms, improvement in functional class and exercise class, decreased morbidity, and preventing mortality. Combination therapy in the treatment of PAH is an emerging therapeutic option. Combining therapies with differing mechanisms of action will maximize therapeutic benefits such as symptom control and increased rate of survival. The updated 2007 American College of Chest Physicians evidence-based clinical practice guidelines recommend combination therapy in functional classes III and IV if there is no improvement with current therapy or if there is deterioration in class. PAH monotherapy has been shown to improve symptoms, but the patients’ hemodynamic parameters may not be normalized, leading to further pulmonary vascular remodeling. Combination therapy offers an additional option for those patients who are unable to stabilize on monotherapy.

Dual therapy in IPAH and SSc-PAH. A qualitative systematic review

BACKGROUND

Use of endothelin receptor antagonists (ERA), phosphodiesterase type-5 (PDE-5) inhibitors and prostaglandin analogues has resulted in improved outcomes in idiopathic pulmonary arterial hypertension (IPAH) and systemic sclerosis-associated PAH (SSc-PAH) patients. However, patients often deteriorate on monotherapy. The objective of this study is to evaluate the effect of dual therapy on outcomes in IPAH and SSc-PAH.

METHODS

A systematic review of MEDLINE (1950-2011), EMBASE (1980-2011) and CINAHL (inception-2011) was conducted to identify studies that evaluated the effect of any dual combination of ERA, PDE-5 inhibitors or prostaglandin analogues on 6-min walk distance (6MWD), functional class (FC), haemodynamics, quality-of-life (QoL) or time-to-clinical-worsening in IPAH or SSc-PAH. A standardized form was used to abstract design, sample size, aetiology, outcome and treatment effect.

RESULTS

Twenty-six observational studies and 6 randomized trials were identified. Using combination PDE-5 inhibitor and prostaglandin analogues, 6/7 studies reported improvement in 6MWD, 6/8 studies reported improvement in FC, 6/6 studies reported improvement in haemodynamics and 1 trial demonstrated improvement in QoL and time-to-clinical-worsening. Using combination ERA and prostaglandin analogues, 4/6 studies and 1 trial reported improvement in 6MWD, 3/3 studies and 1 trial reported improvement in FC, 4/5 studies and 1 trial reported improvement in PAP. Using combination ERA and PDE-5 inhibitor, 4/7 studies reported an improvement in 6MWD, and 2/6 report improvement in FC.

CONCLUSION

The evidence suggests a beneficial effect of dual therapy in IPAH and SSc-PAH, particularly those who are deteriorating on monotherapy. Research should focus on subsets of patients to identify the optimal timing and combination of dual therapy.

A phase III, multicenter, collaborative, open-label clinical trial of sildenafil in Japanese patients with pulmonary arterial hypertension

BACKGROUND

There is evidence that phosphodiesterase type-5 is effective for the treatment of pulmonary arterial hypertension (PAH).

METHODS AND RESULTS

A phase III, multicenter, open-label clinical trial of sildenafil 20mg t.i.d. was conducted in 21 Japanese patients with PAH to examine its efficacy, safety, and pharmacokinetics. The present trial consisted of a screening period and 12-week treatment. Patients who were enrolled in the present trial increased their 6-min walking distance of administration increased at week 12 by 84.2m from baseline. Hemodynamic parameters (eg, mean pulmonary artery pressure and pulmonary vascular resistance), Borg dyspnea scores, and plasma brain natriuretic peptide concentrations also improved compared to baseline. Most patients improved or sustained WHO functional class. Seven subjects, who were examined for the pharmacokinetics of sildefanil, showed relatively large interindividual variations in the C(max), AUC(0-8), C(ss,av), and C(trough) of the drug. Any serious adverse events, severe adverse events, and deaths were not observed. Most of events of undeniable causality were mild or moderate in severity. Sildefanil was well tolerated by the subjects.

CONCLUSIONS

Sildenafil 20mg t.i.d. was effective and safe for Japanese patients with PAH.

Sildenafil for the treatment of pulmonary hypertension in pediatric patients

Sildenafil is a phosphodiesterase 5 inhibitor widely used for the treatment of pulmonary hypertension in children. Despite limited available safety and efficacy evidence, use of sildenafil continues to increase. To date, sildenafil use for pediatric pulmonary hypertension has been characterized for 193 children through 16 studies and 28 case series and reports. The primary efficacy data suggest that sildenafil is beneficial for facilitating the weaning of inhaled nitric oxide in children after cardiac surgery. Compiled safety data suggest that sildenafil is well tolerated among children with idiopathic pulmonary arterial hypertension and pulmonary arterial hypertension associated with congenital heart disease. This review summarizes the available data describing the use, safety, and efficacy of sildenafil for children with pulmonary hypertension.

Effects of sildenafil on the fetal growth of guinea pigs and their ability to survive induced intrapartum asphyxia

OBJECTIVE

Our goal was to determine whether sildenafil increased fetal weight and favored fetal tolerance to induced asphyxia at birth in guinea pigs.

STUDY DESIGN

Twenty guinea pigs were randomly allocated to placebo (n = 10) or sildenafil 50 microg/kg (n = 5) or 500 microg/kg (n = 5), starting from day 35 of gestation to delivery. Fetuses were delivered by cesarean section. Fetal asphyxia was induced by clamping the umbilical cord at birth for 5 minutes.

RESULTS

Sildenafil protected the pups against induced asphyxia at birth in a dose-dependent manner (eg, partial pressure (tension) of carbon dioxide levels were 75.9 +/- 19.3, 66.9 +/- 18.8, and 54.8 +/- 13.0 in the control and low- and high-dose sildenafil groups, respectively). The high-dose sildenafil group of piglets gained 1.5 times more body weight.

CONCLUSION

In guinea pigs, low doses of sildenafil administered from day 35 to the end of gestation favored fetal tolerability to induced intrapartum asphyxia. High doses of sildenafil increased fetal weight.

Safety and efficacy of transition from subcutaneous treprostinil to oral sildenafil in patients with pulmonary arterial hypertension

BACKGROUND

Sildenafil is a selective inhibitor of phosphodiesterase type 5 (PDE5), and has been shown to improve 6-minute walk distance (SMWD) and World Health Organization (WHO) functional class in patients with idiopathic pulmonary arterial hypertension (iPAH) and PAH associated with connective tissue disease or with repaired congenital systemic-to-pulmonary shunts. Despite the efficacy of sildenafil in patients on conventional therapy with diuretics and anti-coagulants, little is known of the safety and efficacy of transitioning patients already established on parenteral prostanoid therapy to sildenafil.

METHODS

We studied 14 patients on long-term subcutaneous treprostinil for PAH (from a cohort of 51 patients [27%]), who wished to discontinue treatment because of injection-site pain. The etiology of their PAH included iPAH (7 of 14), PAH secondary to scleroderma (2 of 14), thromboembolic disease (3 of 14) and PAH post-surgical correction of ventricular septal defect (2 of 14). Treprostinil was gradually weaned and all patients were started open-label with 50 mg sildenafil four times per day for 3 months. New York Heart Association (NYHA) functional class, SMWD, echocardiogram and quality-of-life (QOL) measures were determined at baseline and after 3 months of therapy with sildenafil.

RESULTS

Of 14 patients, 4 discontinued the transition because of deterioration during treprostinil withdrawal, despite the introduction of sildenafil. Replacement of chronic subcutaneous treprostinil with sildenafil was possible in 10 of 14 patients (71%), who demonstrated stable NYHA class (mean +/- SD: 3.1 +/- 0.3 at baseline to 2.6 +/- 0.8 at 3 months, p = 0.138), stable SMWD (434 +/- 83 m at baseline, 451 +/- 72 at 3 months, p = 0.23) and significantly improved QOL measures at 3 months.

CONCLUSIONS

The transition from subcutaneous treprostinil to sildenafil was safely achieved in most (71%), but not all, patients with pulmonary arterial hypertension of varied etiology. These patients had an improvement in both NYHA functional class and QOL, and maintained stable walk distances over a 3-month period on sildenafil therapy.