Combination therapy and new types of agents for pulmonary arterial hypertension

Recent Advances in the Treatment of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a disease in which stenosis or obstruction of the pulmonary arteries (PAs) causes an increase in PA pressure, leading to right-sided heart failure and death. Basic research has revealed a decrease in the levels of endogenous vasodilators, such as prostacyclin, and an increase in the levels of endogenous vasoconstrictors, such as endothelin, in patients with PAH, leading to the development of therapeutic agents. Currently, therapeutic agents for PAH target three pathways that are selective for PAs: the prostacyclin, endothelin, and nitric oxide pathways. These treatments improve the prognosis of PAH patients. In this review, we introduce new drug therapies and provide an overview of the current therapeutic agents.

An Update on Advancements and Challenges in Inhalational Drug Delivery for Pulmonary Arterial Hypertension

A lethal condition at the arterial–alveolar juncture caused the exhaustive remodeling of pulmonary arterioles and persistent vasoconstriction, followed by a cumulative augmentation of resistance at the pulmonary vascular and, consequently, right-heart collapse. The selective dilation of the pulmonary endothelium and remodeled vasculature can be achieved by using targeted drug delivery in PAH. Although 12 therapeutics were approved by the FDA for PAH, because of traditional non-specific targeting, they suffered from inconsistent drug release. Despite available inhalation delivery platforms, drug particle deposition into the microenvironment of the pulmonary vasculature and the consequent efficacy of molecules are influenced by pathophysiological conditions, the characteristics of aerosolized mist, and formulations. Uncertainty exists in peripheral hemodynamics outside the pulmonary vasculature and extra-pulmonary side effects, which may be further exacerbated by underlying disease states. The speedy improvement of arterial pressure is possible via the inhalation route because it has direct access to pulmonary arterioles. Additionally, closed particle deposition and accumulation in diseased tissues benefit the restoration of remolded arterioles by reducing fallacious drug deposition in other organs. This review is designed to decipher the pathological changes that should be taken into account when targeting the underlying pulmonary endothelial vasculature, especially with regard to inhaled particle deposition in the alveolar vasculature and characteristic formulations.

Investigation of mutual pharmacokinetic interactions between macitentan, a novel endothelin receptor antagonist, and sildenafil in healthy subjects

AIM

To study the mutual pharmacokinetic interactions between macitentan, an endothelin receptor antagonist, and sildenafil in healthy male subjects.

METHODS

In this open-label, randomized, three way crossover study, 12 healthy male subjects received the following oral treatments: A) a loading dose of 30 mg macitentan on day 1 followed by 10 mg once daily for 3 days, B) sildenafil 20 mg three times a day for 3 days and a single 20 mg dose on day 4 and C) both treatments A and B concomitantly. Plasma concentration-time profiles of macitentan and its active metabolite ACT-132577 (treatments A and C) and sildenafil and its N-desmethyl metabolite (treatments B and C) were determined on day 4 and analyzed non-compartmentally.

RESULTS

The pharmacokinetics of macitentan were not affected by sildenafil. In the presence of sildenafil Cmax and AUCτ of the metabolite ACT-132577 decreased with geometric mean ratios (90% confidence interval (CI)) of 0.82 (0.76, 0.89) and 0.85 (90% CI 0.80, 0.91), respectively. In the presence of macitentan, plasma concentrations of sildenafil were higher than during treatment with sildenafil alone, resulting in increased Cmax and AUCτ values. The respective geometric mean ratios were 1.26 (90% CI 1.07, 1.48) and 1.15 (90% CI 0.94, 1.41). The pharmacokinetics of N-desmethylsildenafil were not affected by macitentan. All treatments were well tolerated.

CONCLUSION

A minor, not clinically relevant, pharmacokinetic interaction was observed between macitentan and sildenafil. Based on these results, no dose adjustment of either compound appears necessary during concomitant treatment with macitentan and sildenafil.

Dual phosphodiesterase type 5 inhibitor therapy for refractory pulmonary arterial hypertension: a pilot study

BACKGROUND

Recent vasodilating drugs have improved prognosis of Pulmonary arterial hypertension (PAH). Some reports describe the merits of combination therapies for PAH, and this study evaluated the efficacy and safety of phosphodiesterase type 5 inhibitors (PDE5i) combination therapy, using sildenafil and tadalafil, for multi-drug-resistant PAH.

METHODS

We retrospectively analyzed 7 consecutive refractory patients with PAH administered either sildenafil 60 mg or tadalafil 40 mg as well as both ERA and prostanoid as combination therapies. All were started on the dual PDE5i (sildenafil and tadalafil at maximum dose).

RESULTS

Treatment was generally well tolerated without severe adverse events. On completion of the study, the seven patients received right heart catheterization and the 6-minute walk test (6WMT) 9.6 ± 1.4 months after initiation of the dual PDE5i therapy, showing significant improvements in hemodynamic parameters and exercise tolerance. Mean pulmonary arterial pressure and pulmonary vascular resistance decreased from 47.9 ± 9.7 to 41.7 ± 9.2 mmHg (P = 0.004) and 9.3 ± 2.7 to 6.7 ± 2.9 mmHg (P = 0.018), respectively. Cardiac index and 6MWT also increased from 2.8 ± 0.9 to 3.1 ± 0.8 L/min/m(2) (P = 0.026) and 353 ± 60 to 382 ± 62 m (P = 0.014), respectively.

CONCLUSION

The findings support dual PDE5i therapy as a new treatment option for refractory PAH.

The role of phosphodiesterase inhibitors in the management of pulmonary vascular diseases

Phosphodiesterase inhibitors (PDE) can be used as therapeutic agents for various diseases such as dementia, depression, schizophrenia and erectile dysfunction in men, as well as congestive heart failure, chronic obstructive pulmonary disease, rheumatoid arthritis, other inflammatory diseases, diabetes and various other conditions. In this review we will concentrate on one type of PDE, mainly PDE5 and its role in pulmonary vascular diseases.

An update on medical therapy for pulmonary arterial hypertension

Over the past 20 years, great progress has been made in the treatment of pulmonary arterial hypertension (PAH). Available therapies target one of three principal pathways: the endothelin (ET), nitric oxide (NO) or the prostacyclin (PGI2) pathway. Evidence shows that current drugs, used either as monotherapy or in different combinations, can improve exercise capacity, clinical symptoms, hemodynamics and even survival in PAH. Unfortunately, the disease remains incurable and the prognosis of the disease is still poor. However, existing and novel potent antiproliferative therapies are being explored, and new agents targeting different and/or additional pathways are likely to become available to clinicians in the near future. Promising candidates include tyrosine kinase antagonists (e.g. imatinib); soluble guanylate cyclase stimulators (riociguat); an oral analog of prostacyclin (selexipag); and a tissue targeting endothelin receptor antagonist (macitentan). Phase II or III trials have either been completed or are underway to evaluate the safety and efficacy of these various therapies.

Pulmonary arterial hypertension associated with systemic sclerosis: Current diagnostic approach and therapeutic strategies

Pulmonary arterial hypertension (PAH) represents a devastating vascular complication of systemic sclerosis (SSc) and is found in 10%-15% of cases carrying a severe prognosis. PAH has a dramatic impact on the clinical course and overall survival, being the single most common cause of death in patients with this entity. The clinical course and aggressive progression of PAH has led clinicians to perform annual screening for it, since early detection and diagnosis are the cornerstone of a prompt therapeutic intervention. The diagnosis of PAH can be challenging to clinicians, particularly in its early stages, since in the context of SSc, the multiple causes of dyspnea need to be assessed. Doppler echocardiography represents the best initial screening tool, however, right heart catheterization remains the gold standard and definitive diagnostic means. Remarkable advances have been achieved in elucidating the pathogenesis of PAH in the past two decades, leading to the development of disease-specific targeted therapies: prostacyclin analogues, endothelin receptor antagonists and inhibitors of five phosphodiesterase pathways. However, the clinical response to these therapies in SSc-associated PAH has not been as great as the one seen with idiopathic PAH. This review also focuses on the diagnosis and novel therapies that are currently available for PAH, as well as potential future therapeutic developments based on newly acquired knowledge of diverse pathogenic mechanisms.

IVI epoprostenol as salvage therapy in pulmonary arterial hypertension: an Australian perspective

BACKGROUND

IVI epoprostenol is the only therapy for pulmonary arterial hypertension (PAH) with a randomized controlled trial demonstrating improved survival, when used as first-line monotherapy. In Australia it is used as salvage therapy for those failing treatment with other targeted therapies or presenting in World Health Organization functional class (FC) IV.

AIMS

Report experience with IVI epoprostenol, administered as salvage therapy for the treatment of adults with PAH in a single Australian PAH centre.

METHODS

Retrospective case series of all patients commenced on IVI epoprostenol for PAH, between 2002 and 2010. Review of case notes with collection of data at baseline and after treatment, including FC, 6-min walk test (6MWT), right ventricular systolic pressure (RVSP) on echocardiogram, patient survival and treatment complications. Change in indices was assessed using the Wilcoxon Sign Rank Test and is expressed as median (inter-quartile range).

RESULTS

A total of 23 patients was included. Treatment was generally well tolerated with few major complications. At the end of the study period, nine patients were successfully bridged to transplant, five had a sustained response to IVI epoprostenol, six had an incomplete response but were clinically stabilized, two died awaiting transplant and one died who was not a candidate for transplantation. Overall, when measured at best level post initiation of IVI epoprostenol, there were significant improvements in FC -1 [0 to -1] (P < 0.0001), 6MWT (m) +117 [70-264] (P= 0.002) and RVSP (mmHg) -7.0 [4.0 to -45] (P= 0.03).

CONCLUSION

Findings support efficacy of epoprostenol as salvage therapy for patients with PAH.

Treatment of pulmonary arterial hypertension with targeted therapies

Pulmonary arterial hypertension (PAH) is a rare disorder characterized by progressive obliteration of the pulmonary microvasculature that results in elevated pulmonary vascular resistance and premature death. Although no cure exists for PAH, improved understanding of the pathobiological mechanisms of this disease has resulted in the development of effective therapies that target specific aberrant pathways. Agents that modulate abnormalities in the prostacyclin, endothelin, and nitric oxide pathways have been shown in randomized, controlled studies to confer improvements in functional status, pulmonary hemodynamics, and possibly even slow disease progression. Several additional pathways believed to play an important role in the pathogenesis of PAH have been identified as potentially useful therapeutic targets and a number of investigative approaches focusing on these targets are in active development. In this Review, we highlight the pharmacological agents currently available for the treatment of PAH and discuss potential novel strategies.

Is a regenerative approach viable for the treatment of COPD?

Degenerative lung diseases such as chronic obstructive pulmonary disease (COPD) are common with huge worldwide morbidity. Anti-inflammatory drug development strategies have proved disappointing and current treatment is aimed at symptomatic relief. Only lung transplantation with all its attendant difficulties offers hope of cure and the outlook for affected patients is bleak. Lung regeneration therapies aim to reverse the structural and functional deficits in COPD either by delivery of exogenous lung cells to replace lost tissue, delivery of exogenous stem cells to induce a local paracrine effect probably through an anti-inflammatory action or by the administration of small molecules to stimulate the endogenous regenerative ability of lung cells. In animal models of emphysema and disrupted alveolar development each of these strategies has shown some success but there are potential tumour-inducing dangers with a cellular approach. Small molecules such as all-trans retinoic acid have been successful in animal models although the mechanism is not completely understood. There are currently two Pharma-sponsored trials in progress concerning patients with COPD, one of a specific retinoic acid receptor gamma agonist and another using mesenchymal stem cells.

Endothelin receptor antagonists for the treatment of pulmonary arterial hypertension

INTRODUCTION

Endothelin is a key mediator in the pathophysiology of pulmonary arterial hypertension (PAH). Its effects are mediated through the activation of two associated receptor subtypes, termed A and B. Therapeutic strategies that modulate the activity of endothelin are, therefore, of interest to improve the functional status of patients with PAH.

AREAS COVERED

The rationale for the use of endothelin receptor antagonists as a therapeutic class in PAH and pertinent data from important clinical studies are presented in this review. Areas for future research are also suggested.

EXPERT OPINION

The availability of the endothelin receptor antagonist class of agents represents a significant addition to the therapeutic armamentarium which is available for the treatment of PAH. Comparative studies are warranted to establish whether selective endothelin-A receptor antagonism is more advantageous than dual receptor antagonism. Future studies of endothelin receptor antagonists will increasingly focus on the potential of a combination of different PAH therapeutic classes and will employ 'harder' clinical end points. This is of crucial importance to ensure that future developments are both worthwhile and acceptable to patients, physicians, health system payers and regulatory authorities.

Pulmonary veno-occlusive disease: the bête noire of pulmonary hypertension in connective tissue diseases?

Pulmonary veno-occlusive disease (PVOD) is a rare form of pulmonary hypertension that may develop in patients with connective tissue diseases (CTD). Most cases have been reported in patients with systemic sclerosis, though associations with systemic lupus erythematosis and mixed connective tissue disease have also been described. PVOD is characterised by progressive obstruction of small pulmonary veins and venules that leads to increased pulmonary vascular resistance, right heart failure and premature death. Distinguishing PVOD from pulmonary arterial hypertension (PAH) is often difficult, though use of a diagnostic algorithm may improve diagnostic accuracy and preclude recourse to lung biopsy. The finding of normal left-heart filling pressures in the context of radiological studies suggestive of pulmonary oedema is an important diagnostic clue, particularly if this clinical scenario coincides with the introduction of vasodilator therapy. There are no approved treatments for the disorder, though cautious use of PAH specific therapy may improve short-term outcomes in selected idiopathic PVOD cases. This review summarises the epidemiologic, clinico-pathologic and imaging characteristics of PVOD in the setting of CTD and discusses potential management approaches.

Management of dyspnea in advanced pulmonary arterial hypertension

PURPOSE OF REVIEW

Pulmonary hypertension leads to progressive increase in pulmonary vascular resistance, heart failure, and death. Pulmonary arterial hypertension (PAH) is a subset of pulmonary hypertension affecting small pulmonary arteries and not associated with underlying heart or lung disease. Dyspnea and exercise intolerance are hallmarks of PAH and are used to monitor disease progression. This review focuses on recent advances in the pathophysiology and treatment of dyspnea in PAH.

RECENT FINDINGS

The etiological classification of pulmonary hypertension and World Health Organization functional class clinical classification, as used to guide management, have recently been revised. Dyspnea and PAH disease progression are best assessed by cardiopulmonary exercise testing and the six-minute walk test. Understanding of the molecular pathogenesis of PAH has led to new classes of treatments, including prostacyclin analogues, endothelin receptor antagonists, and phosphodiesterase-5 inhibitors. Prostanoids have the longest track record in treatment of PAH but a short half-life and cumbersome delivery systems limit their utility. More convenient endothelin receptor antagonists are becoming mainstream in PAH management. Phosphodiesterase-5 inhibitors improve exercise capacity and quality of life, although long-term outcome data are pending. Combination therapy with different medication classes appears promising for progressive disease.

SUMMARY

Establishing the cause and clinical severity of pulmonary hypertension is critical for management. The pathophysiology of dyspnea in PAH is complex and related to pulmonary vascular resistance. Although disease-specific treatments are now available, a cure for PAH remains elusive and trials of combination treatments to improve symptoms and outcomes are ongoing.

Evidence for the use of combination targeted therapeutic approaches for the management of pulmonary arterial hypertension

The last decade has witnessed a remarkable increase in the number of effective treatment options available for the management of patients with pulmonary arterial hypertension. In this regard, agents belonging to the therapeutic classes that specifically target the prostacyclin, endothelin and nitric oxide pathways have shown the greatest efficacy in clinical studies to date. These various drug treatments have individually been shown to confer improvements in symptoms, exercise capacity, pulmonary haemodynamics and possibly survival in different patient subgroups. However, pulmonary arterial hypertension is characterised by dysregulation of a variety of pathways. In addition, disease worsening is inevitable for the majority of patients receiving monotherapy. As a consequence, there is increasing interest in the use of treatment combinations in order to target multiple targets with the aim of restoring normal pulmonary vascular function in order to improve clinical status. Indeed, use of multiple specific-treatment regimens is now part of routine clinical practice and is emphasized in recently published therapeutic guidelines. This review details the rationale for the different combination strategies and examines the clinical evidence in favour of some of the approaches that have been evaluated.

Pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a devastating disease with significant disability and mortality, and it has much higher prevalence than previously thought. During the past 15 years, we have witnessed remarkable advances in our understanding of pathogenesis, in diagnostic process and in the development of disease-specific treatments for PAH. Nowadays, the diagnosis is more clearly defined, non-invasive markers of disease severity can be widely applied, and finally we can adopt evidence-based treatment. Newer drugs availability has resulted in radical change in the management of this disease. The article reviews established approaches to evaluation and treatment of this disorder.

Adrenomedullin promotes lung angiogenesis, alveolar development, and repair

Bronchopulmonary dysplasia (BPD) and emphysema are significant global health problems at the extreme stages of life. Both are characterized by alveolar simplification and abnormal distal airspace enlargement due to arrested development or loss of alveoli, respectively. Both lack effective treatments. Mechanisms that inhibit distal lung growth are poorly understood. Adrenomedullin (AM), a recently discovered potent vasodilator, promotes angiogenesis and has protective effects on the cardiovascular and respiratory system. Its role in the developing lung is unknown. We hypothesized that AM promotes lung angiogenesis and alveolar development. Accordingly, we report that lung mRNA expression of AM increases during normal alveolar development. In vivo, intranasal administration of the AM antagonist, AM22-52 decreases lung capillary density (12.4 +/- 1.5 versus 18 +/- 1.5 in control animals; P < 0.05) and impairs alveolar development (mean linear intercept, 52.3 +/- 1.5 versus 43.8 +/- 1.8 [P < 0.05] and septal counts 62.0 +/- 2.7 versus 90.4 +/- 3.5 [P < 0.05]) in neonatal rats, resulting in larger and fewer alveoli, reminiscent of BPD. This was associated with decreased lung endothelial nitric oxide synthase and vascular endothelial growth factor-A mRNA expression. In experimental oxygen-induced BPD, a model of arrested lung vascular and alveolar growth, AM attenuates arrested lung angiogenesis (vessel density, 6.9 +/- 1.1 versus 16.2 +/- 1.3, P < 0.05) and alveolar development (mean linear intercept, 51.9 +/- 3.2 versus 44.4 +/- 0.7, septal counts 47.6 +/- 3.4 versus 67.7 +/- 4.0, P < 0.05), an effect in part mediated by inhibition of apoptosis. AM also prevents pulmonary hypertension in this model, as assessed by decreased right ventricular hypertrophy and pulmonary artery medial wall thickness. Our findings suggest a role for AM during normal alveolar development. AM may have therapeutic potential in diseases associated with alveolar injury.

Addition of sildenafil in patients with pulmonary arterial hypertension with inadequate response to bosentan monotherapy

BACKGROUND

Pulmonary arterial hypertension (PAH) remains a progressive disease despite improvement when using one of three medication classes: prostanoids, endothelin receptor antagonists or phosphodiesterase-5 inhibitors. Combination therapy has been proposed for patients with unsatisfactory response to monotherapy.

OBJECTIVES

To examine the effect of adding sildenafil to bosentan on 6 min walk distance (6MWD) and New York Heart Association (NYHA) classification in patients with PAH who achieved inadequate improvement with bosentan monotherapy.

METHODS

Patients with idiopathic PAH or connective tissue disease-associated PAH, and who had either self-reported inadequate improvement in exercise tolerance or a decline in 6MWD after initial improvement, were included in the study (n=10). Data on 6MWD and NYHA class at baseline (before initiation of bosentan), three and six months after baseline, second baseline (before initiation of combination therapy with sildenafil), and three and six months after second baseline were analyzed for any changes.

RESULTS

Mean time from initiation of bosentan monotherapy to initiation of combination therapy was 558 days (range 150 to 900 days). Six months after initiation of bosentan, 6MWD increased by 57.2 m above the baseline of 314.4 m. Six months after combination therapy, 6MWD was 62.80 m higher than the baseline before initiation of combination therapy of 339 m (P<0.02). The overall increase in 6MWD six months after combination therapy was higher than the first baseline by 87.4 m (P not significant). NYHA functional class did not improve with combination therapy in all patients.

DISCUSSION

Initiating combination therapy in patients who achieve an inadequate improvement in exercise tolerance with monotherapy may result in further improvement in exercise tolerance.

Pulmonary hypertension: diagnosis and management

Pulmonary arterial hypertension is a progressive, symptomatic, and ultimately fatal disorder for which substantial advances in treatment have been made during the past decade. Effective management requires timely recognition and accurate diagnosis of the disorder and appropriate selection among therapeutic alternatives. Despite progress in treatment, obstacles remain that impede the achievement of optimal outcomes. The current article provides an overview of the pathobiologic mechanisms of pulmonary arterial hypertension, including genetic substrates and molecular and cellular mechanisms, and describes the clinical manifestations and classification of pulmonary arterial hypertension. The article also reviews established approaches to evaluation and treatment, with emphasis on the appropriate application of calcium channel blockers, prostacyclin analogues, endothelin receptor antagonists, and phosphodiesterase 5 inhibitors. In addition, the authors discuss unresolved issues that may complicate patient management, such as the clinical importance of mild or exercise-related pulmonary arterial hypertension, and they identify avenues by which treatment may advance in the future through the use of combination treatment, outcomes assessment, and exploration of alternative pharmacologic strategies.

Pulmonary hypertension: diagnosis and management

Pulmonary arterial hypertension is a progressive, symptomatic, and ultimately fatal disorder for which substantial advances in treatment have been made during the past decade. Effective management requires timely recognition and accurate diagnosis of the disorder and appropriate selection among therapeutic alternatives. Despite progress in treatment, obstacles remain that impede the achievement of optimal outcomes. The current article provides an overview of the pathobiologic mechanisms of pulmonary arterial hypertension, including genetic substrates and molecular and cellular mechanisms, and describes the clinical manifestations and classification of pulmonary arterial hypertension. The article also reviews established approaches to evaluation and treatment, with emphasis on the appropriate application of calcium channel blockers, prostacyclin analogues, endothelin receptor antagonists, and phosphodiesterase 5 inhibitors. In addition, the authors discuss unresolved issues that may complicate patient management, such as the clinical importance of mild or exercise-related pulmonary arterial hypertension, and they identify avenues by which treatment may advance in the future through the use of combination treatment, outcomes assessment, and exploration of alternative pharmacologic strategies.

Pulmonary hypertension in interstitial lung disease

PURPOSE OF REVIEW

To examine recent advances in the understanding of the prevalence, pathophysiology, natural history, diagnosis, and treatment of pulmonary hypertension associated with interstitial lung disease.

RECENT FINDINGS

Significant progress has recently been made in understanding the etiology of various causes of pulmonary hypertension, including those associated with interstitial lung disease, and new data regarding the various pathophysiologic mechanisms of pulmonary hypertension in interstitial lung disease have been published. Therapeutic agents that were initially studied in patients with idiopathic pulmonary arterial hypertension are now being applied to interstitial lung disease-related pulmonary hypertension. Short-term hemodynamic benefits and disease-related quality of life outcomes that are associated with these advanced therapies are now better understood, but data regarding long-term outcomes and the efficacy of combination therapies remain lacking for interstitial lung disease-related pulmonary hypertension. Lung transplantation outcomes in the treatment of pulmonary hypertension associated with interstitial lung disease have been further defined.

SUMMARY

Pulmonary hypertension associated with interstitial lung disease is now frequently recognized and is associated with substantial morbidity and mortality. Various new pharmacotherapies as well as lung transplantation are increasing the treatment options for these disorders, although timing of advanced therapies and long-term benefits and toxicities remain uncertain.

ERG evaluation of daily, high-dose sildenafil usage

PURPOSE

Sildenafil can cause transient, mild ERG changes in healthy individuals taking large single doses. Although the drug was originally intended for intermittent use in erectile dysfunction, it has now been approved for chronic use in subjects with pulmonary arterial hypertension (PAH). The purpose of our study is to investigate possible ERG changes in subjects using large doses of sildenafil on a chronic daily basis.

METHODS

We examined five subjects with PAH taking sildenafil daily for 1-4 years. Full-field electroretinogram (ERG), multifocal ERG (mfERG), and color testing were performed. Three of the subjects returned on a later date for challenge off and on the medication.

RESULTS

On chronic daily sildenafil, color vision testing was normal, and ERG and mfERG amplitudes were normal; however, cone implicit times on drug were modestly lengthened. There were no consistent full-field ERG changes when off the drug, but the mfERG showed a small amplitude increase and implicit time decrease, which returned 1 h after re-dosing.

CONCLUSION

There was a modest lengthening of cone implicit time on chronic daily doses of sildenafil and a hint that some of these changes may be reversible in the short term. It does not appear that chronic sildenafil usage at these dosage levels is seriously toxic or threatening to vision.

Serotonin: a review

5-Hydroxytryptamine, or serotonin, is a biogenic amine most noted for its role as a neurotransmitter. Manipulation of serotonin in animal models was used as a tool for studying its role in humans. Through such research serotonin has been shown to modulate gastrointestinal motility, peripheral vascular tone, cerebral vascular tone, and platelet function and has been implicated in the pathophysiology of mood disorders, emesis, migraine, irritable bowel syndrome (IBS), and pulmonary and systemic hypertension. The knowledge gained is being directly applied back to animals in research on drugs that manipulate the serotonergic system in dogs and cats. Increasing use and availability of drugs that manipulate the serotonergic system has created a circumstance through which a novel toxicity was discovered in both humans and animals. Serotonin Syndrome describes the clinical picture seen in humans and animals with serotonin toxicity. This paper provides a review the physiology of serotonin and its involvement in the pathophysiologic mechanisms of various conditions, including the Serotonin Syndrome.

Pulmonary hypertension: evaluation and management

Pulmonary hypertension (PH) is a hemodynamic state characterized by elevation in the mean pulmonary arterial pressure and pulmonary vascular resistance leading to right ventricular failure and premature death. PH can be the result of a variety of diseases of different etiologies. Pulmonary arterial hypertension (PAH) should be distinctly differentiated from pulmonary venous hypertension (PVH) as a result of left heart disease. PAH is commonly caused by or associated with an underlying pulmonary, cardiac, or systemic disease (APAH). In the absence of an identifiable etiology or associated underlying disease, PAH is referred to as idiopathic (IPAH). IPAH, formerly known as primary pulmonary hypertension (PPH), is a rare disease most commonly seen in women of childbearing age. Presenting symptoms and signs are nonspecific and include dyspnea on exertion, fatigue, and a loud pulmonary component of the second heart sound. Transthoracic Doppler echocardiography is an excellent noninvasive test to detect the presence of pulmonary hypertension, although every patient should receive a right heart catheterization to confirm the diagnosis. A detailed work up, including laboratory tests and imaging studies, is also indicated to rule out known causes of pulmonary hypertension. Several targeted treatment options have become available in recent years and include parenteral and inhaled prostanoids, oral endothelin receptor antagonists, and oral phosphodiesterase type-5 inhibitors. As a result of their complex care, patients should be referred to centers with expertise in pulmonary hypertension.