Medical Therapy for Pulmonary Arterial Hypertension^*: Updated ACCP Evidence-Based Clinical Practice Guidelines FREE TO VIEW

Pulmonary arterial hypertension (PAH), defined as a mean pulmonary artery pressure (PAPm) ≥ 25 mm Hg with a pulmonary capillary wedge pressure ≤ 15 mm Hg measured by cardiac catheterization, is a disorder that may occur either in the setting of a variety of underlying medical conditions or as a disease that uniquely affects the pulmonary circulation. Irrespective of its etiology, PAH is a serious and often progressive disorder that results in right ventricular dysfunction and impairment in activity tolerance, and may lead to right-heart failure and death. The pathogenesis of PAH is complex and incompletely understood, but includes both genetic and environmental factors that alter vascular structure and function.

Dramatic advances in the treatment of PAH have occurred over the past 2 decades, based in part on seminal observations on pathogenesis made in the research laboratory. Recognizing the need to educate physicians on the diagnosis and management of PAH, the American College of Chest Physicians (ACCP) convened a multidisciplinary panel of experts from 2003 to 2004 to formulate guidelines for the approach to management of this complex condition. These evidence-based guidelines, including a comprehensive overview of treatment,¹ were published as a supplement to CHEST in 2004.^12345678 The guidelines from this original publication are presented in Table 1.

The pace of developments in the treatment for PAH has quickened, with several important clinical trials having been published over the past 2 years that have led to regulatory approval of newer drugs and experience with combinations of existing drugs. These advances are likely to impact on the way physicians should now approach the treatment of PAH. Accordingly, the ACCP impaneled a subcommittee of the original panel to develop an update to the treatment guidelines based on these recent developments. As before, these guidelines are evidence based and the subcommittee employed the same criteria for inclusion and recommendation as were used in the previous work.

A consensus panel convened by the ACCP developed guidelines for the diagnosis and treatment of PAH that were published in 2004.⁹ Subsequently, several important clinical trials have been published and new treatments have received regulatory approval. In addition, add-on and combination therapy are being explored, which promise to open new therapeutic avenues.

Therefore, the Health and Science Policy Committee of the ACCP authorized an update of the medical treatment guidelines.¹ Lewis Rubin, MD, FCCP, was again selected to chair the panel. A small subset of authors from the original guideline were requested to participate in the update. In October 2005, the group met in Montreal to plan the revision and to cultivate consensus on the approach to the new treatment algorithm.

The authors performed computerized searches of the literature for studies on the medical treatment of PAH that were published prior to September 1, 2006. Only English-language articles were included. We selected studies of therapeutic agents in the following classes: prostanoids, endothelin receptor antagonists, and phophodiesterase inhibitors. As in the previous guidelines,¹ we considered studies conducted among patients with known or suspected idiopathic PAH (IPAH) or PAH occurring in association with underlying collagen vascular disease, and congenital heart disease. Also in a manner consistent with the previous statement, we excluded studies of pulmonary hypertension (PH) associated with COPD or other parenchymal lung disease, high-altitude PH, or cardiac disease (eg, left-heart failure, valvular heart disease) except congenital heart disease. This article provides an update to the previously published guidelines based on this current body of literature. The original guidelines have been summarized, a discussion of new studies has been added, and the treatment algorithm has been revised to take into account recent developments in therapy. The recommendations in this guideline, like those in the 2004 edition, are based on the same grading system (Table 2 ), in which the strength of the recommendation results from the interaction of two components: the quality of the evidence, and the net benefit of the therapy to the patient⁴ (Table 3 ).

This update provides evidence-based treatment recommendations for physicians involved in the care of patients with PAH. No financial support was provided by any pharmaceutical companies for the development of this update. Any conflicts of interest were required to be disclosed by all authors and included in this document. This guideline was reviewed and approved by the Pulmonary Vascular NetWork, Health and Science Policy Committee, and ultimately by the Board of Regents of the ACCP.

A small number of patients with IPAH, who demonstrate a favorable response to acute vasodilator testing at the time of cardiac catheterization, will do well with calcium-channel blocker (CCB) therapy. Since publication of the original ACCP guidelines, an important article¹⁰ has further clarified the role of CCBs in the IPAH population. Sitbon and colleagues¹⁰ reported results of a retrospective analysis of 557 IPAH patients tested acutely with IV epoprostenol or inhaled nitric oxide. Using a criteria of a > 20% decrease in both PAPm and pulmonary vascular resistance (PVR), only 70 patients (12.6%) displayed vasoreactivity. Long-term CCB responders were defined as patients in New York Heart Association (NYHA) functional class I or II with a sustained hemodynamic improvement after at least 1 year without the addition of other PAH-specific therapy. Of the 70 patients who displayed acute vasoreactivity, only 38 patients (6.8% of the overall study group) had a favorable long-term clinical response to long-term CCB therapy. These patients exhibited a more pronounced reduction in PAPm, reaching an absolute PAPm of 33 ± 8 mm Hg (± SD) with acute vasodilator testing. As a result, the consensus definition of a favorable response is now defined as a fall in PAPm ≥ 10 mm Hg, to a PAPm ≤ 40 mm Hg, with an unchanged or increased cardiac output. Patients with IPAH who meet these criteria may be treated with CCBs. True responders to vasodilators (CCBs) are very uncommon among patients with other forms of PAH (non-IPAH, or PAH occurring in association with underlying disease processes). Long-acting nifedipine or diltiazem, or amlodipine are suggested. Due to its potential negative inotropic effects, verapamil should be avoided. Patients should be followed up closely for both safety and efficacy, with an initial reassessment after 3 months of therapy.¹⁰ If a patient does not improve to functional class I or II, additional or alternative PAH therapy should be instituted.

In a 12-week, prospective, multicenter, randomized, controlled, open-label trial,¹¹ continuously IV infused epoprostenol plus conventional therapy (including oral vasodilators [CCBs], anticoagulation, diuretic, digoxin, and oxygen) was compared to conventional therapy alone in 81 patients with severe IPAH (NYHA class III or IV). Exercise capacity improved in the 41 patients treated with epoprostenol (median 6 min walk [6MW] distance, 362 m at 12 weeks, vs 315 m at baseline), and decreased in the 40 patients treated with conventional therapy alone (204 m at 12 weeks vs 270 m at baseline; p < 0.002 for the comparison of the treatment groups). There were also improvements in indexes of the quality of life, hemodynamics, and survival. A multicenter, randomized, controlled, open-label study¹² of long-term IV epoprostenol treatment in patients with PAH occurring in association with the scleroderma spectrum of disease showed improvement in exercise capacity and hemodynamics. Exercise capacity improved with epoprostenol (median 6MW distance, 316 m at 12 weeks, compared with 270 m at baseline) but decreased with conventional therapy (192 m at 12 weeks, compared with 240 m at baseline). The difference between treatment groups in the median distance walked at week 12 was 108 m (95% confidence interval CI, 55.2 m to 180.0 m) [p < 0.001]. Hemodynamics also improved, however a survival advantage was not demonstrated. Two large long term observation series have documented an improvement in survival in patients with IPAH treated with epoprostenol compared to either historical control subjects or predicted survival based on the National Institutes of Health Registry equation.¹³¹⁴

A placebo-controlled trial of subcutaneously infused treprostinil in patients with functional class II, III, or IV PAH (IPAH or PAH associated with connective tissue disease or congenital systemic to pulmonary shunts) demonstrated improved exercise capacity as measured by the 6-min walk (6MW) distance (median between treatment group difference 16 m (p = 0.006).¹⁵ This effect appeared to be dose related, and subcutaneous dosing may be limited by infusion site pain and reaction. Given potential advantages over IV epoprostenol, including a longer half-life, IV treprostinil has been studied recently. In an open-label study, Tapson et al¹⁶ treated 16 functional class III or IV PAH patients with IV treprostinil. After 12 weeks of therapy, 6MW distance improved by a mean of 82 m, from 319 ± 22 to 400 ± 26 m (p = 0.001) [± SE]. There were also improvements in hemodynamics including PAPm (− 4.2 mm Hg, p = 0.03), cardiac index (+ 0.47 L/min/m², p = 0.002), and PVR index (− 9.4 U/m², p = 0.001) at week 12 compared to baseline. One death, which was thought not to be related to the study drug, occurred during the 12-week study in a patient who received 3 days of IV treprostinil and died 2 weeks later. In a similar open-label trial, Gomberg-Maitland et al¹⁷ transitioned 31 functional class II and III PAH patients from IV epoprostenol to IV treprostinil. Twenty-seven patients completed the 12-week study, and 4 patients were transitioned back to epoprostenol. Exercise endurance as measured by the 6MW distance was maintained among the patients completing the transition (438 ± 16 m at baseline, 439 ± 16 m at week 12) [± SD]. At week 12, there was a modest increase in PAPm of 4 ± 1 mm Hg (p < 0.01) and reduction in cardiac index of 0.4 ± 0.1 L/min/m² (p = 0.01). Notably, the dose of IV treprostinil at the end of 12 weeks was more than twice the dose of IV epoprostenol at the start of the study: 83 ng/kg/min vs 40 ng/kg/min. In 2004, the US Food and Drug Administration (FDA) approved the use of IV treprostinil in NYHA functional class II, III, and IV PAH patients in whom subcutaneous infusion is not tolerated.

A 3-month, randomized, double-blind, placebo-controlled, multicenter trial of iloprost via inhalation six to nine times per day utilized a composite primary end point of a 10% improvement in the 6MW distance and NYHA functional class improvement in the absence of clinical deterioration or death.¹⁸ This composite end point was achieved in 17% of treated patients compared to 5% in patients receiving placebo (p = 0.007). The treatment effect on the 6MW distance was a mean increase of 36 m in the overall population in favor of iloprost (p = 0.004) and 59 m in the subgroup of patients with IPAH. Longer-term data regarding inhaled iloprost are conflicting. In a 1-year, open, uncontrolled study¹⁹ of 24 patients with IPAH, aerosolized iloprost at a daily dose of 100 to 150 μg, six to eight inhalations per day improved exercise capacity (mean increase in 6MW distance, 75 m) and pulmonary hemodynamics. More recently, Opitz et al²⁰ prospectively followed up 76 NHYA functional class II or III IPAH patients treated with inhaled iloprost. During the follow-up period of 535 ± 61 days, 11 patients (14%) died, 6 patients (9%) underwent transplantation, 25 patients (33%) were switched to IV prostanoids, 16 patients (23%) received additional/oral PAH therapies, and 12 patients (17%) discontinued inhaled iloprost for other reasons. Event-free survival rates at 1 year and 2 years were 53% and 29%, respectively.

Most recently, inhaled iloprost has been studied in patients who remain symptomatic (NYHA functional class III or IV) while receiving a stable dose of bosentan for at least 3 months.²¹ In this multicenter, placebo-controlled, randomized trial, 67 patients with PAH (94% NYHA functional class III; mean baseline 6MW, 355 m) were randomized to receive inhaled iloprost, (5 μg; six to nine times per day) or placebo. After 12 weeks, the primary efficacy measure, postinhalation 6-min walk distance, improved by 30 m in the iloprost group and 4 m in the placebo group, for a placebo-adjusted difference of + 26 m (p = 0.051). There were also improvements in NYHA functional class (p = 0.002), time to clinical worsening (p = 0.022), and postinhalation PAPm (p < 0.001) and PVR p < 0.001). Combination therapy appeared to be safe and well tolerated. Inhaled iloprost was approved by the FDA in 2004 for functional class III and IV PAH, and in 2005 a brief summary of the results of the add-on study was included in the package insert.

The first randomized, double-blind, placebo-controlled, multicenter study²² of bosentan demonstrated an improvement in the 6MW distance of 70 m (from 360 ± 19 m at baseline to 430 ± 14 m at week 12; p < 0.05), whereas no improvement was seen with placebo (355 ± 25 m at baseline and 349 ± 44 m at week 12). Treatment with bosentan also improved cardiopulmonary hemodynamics and functional class. Asymptomatic increases in hepatic aminotransferases were observed in two bosentan-treated patients. In a second double-blind, placebo-controlled study (the Bosentan Randomized Trial of Endothelin Antagonist Therapy for Pulmonary Hypertension-1 Study²³), bosentan (125 or 250 mg bid) was evaluated in 213 patients with functional class III and IV PAH (either primary or associated with connective tissue disease), for a minimum of 16 weeks (62.5 mg bid for 4 weeks then target dose). Bosentan improved the 6MW distance by 36 m, whereas deterioration (– 8 m) was seen with placebo. The difference between treatment groups in the mean change in 6MW distance was 44 m in favor of bosentan (95% confidence interval, 21 to 67 m; p = 0.0002). The risk of clinical worsening was reduced by bosentan compared to placebo (p = 0.0015, log-rank test). Abnormal hepatic function test findings, syncope, and flushing occurred more frequently in the bosentan group.

Two important articles describing longer-term outcomes with bosentan therapy have been recently published. In the first, McLaughlin et al²⁴ found that first-line therapy with bosentan, with the subsequent addition or transition to other therapy as necessary, resulted in Kaplan-Meier survival estimates of 96% at 12 months and 89% at 24 months. In contrast, predicted survival rates from the National Institutes of Health Registry formula are 69% and 57%, respectively. In addition, at the end of 12 months and 24 months, 85% and 70% of patients, respectively, remained alive and receiving bosentan monotherapy. Factors that predicted a worse outcome included World Health Organization functional class IV and 6MW distance below the median (358 m) at baseline. In the second study, Sitbon et al²⁵ compared survival in patients with functional class III IPAH treated with bosentan with historical data from similar patients treated with epoprostenol. Baseline factors for the 139 patients treated with bosentan and the 346 patients treated with epoprostenol suggested that the epoprostenol cohort had more severe disease. Kaplan-Meier survival estimates after 1 year and 2 years were 97% and 91%, respectively, in the bosentan cohort, and 91% and 84% in the epoprostenol cohort. Cox regression analyses adjusting for differences in baseline factors showed a greater probability of death in the epoprostenol cohort. When matched cohorts of 83 patients each were selected, survival estimates were similar. In the bosentan cohort, 87% and 75% of patients followed up for 1 year and 2 years, respectively, remained on monotherapy. No evidence was found to suggest that initial treatment with oral bosentan, followed by or with the addition of other treatment if needed, adversely affected the long-term outcome compared with initial IV epoprostenol in patients with class III IPAH.

Bosentan has also been studied in children with IPAH and PAH associated with congenital heart disease or connective tissue disease.²⁶ In this retrospective study,²⁶ 86 children started bosentan with or without concomitant IV epoprostenol or subcutaneous treprostinil therapy. At the cutoff date, 68 patients (79%) were still treated with bosentan, 13 patients (15%) had treatment discontinued, and 5 patients (6%) had died. Median exposure to bosentan was 14 months. In 90% of the patients (n = 78), functional class improved (46%) or was unchanged (44%) with bosentan treatment. PAPm and PVR decreased (64 ± 3 to 57 ± 3 mm Hg, p = 0.005; and 20 ± 2 to 15 ± 2 U/m², p = 0.01, respectively; n = 49 [± SEM]). Kaplan-Meier survival estimates at 1 year and 2 years were 98% and 91%, respectively.

Most recently, Galie et al²⁷ reported the results of a multicenter, double-blind, randomized, and placebo-controlled study of bosentan therapy in patients with functional class III Eisenmenger syndrome (Bosentan Randomized Trial of Endothelin Antagonist Therapy for Pulmonary Hypertension-5). Fifty-four patients were randomized 2:1 to bosentan (n = 37) or placebo (n = 17) for 16 weeks. The placebo-corrected effect on systemic pulse oximetry was 1.0% (95% confidence interval, − 0.7 to 2.8), demonstrating that bosentan did not worsen oxygen saturation. Compared with placebo, bosentan reduced PVR index (− 472.0 dyne·s·cm⁻⁵; p = 0.0383). PAPm decreased (− 5.5 mm Hg; p = 0.0363), and exercise capacity increased (53.1 m; p = 0.0079). Treatment was discontinued in four patients as a result of adverse events: two patients (5%) in the bosentan group, and two patients (12%) in the placebo group. Bosentan is currently approved by the FDA for the treatment of patients with functional class III-IV PAH.

In the first randomized, double-blind, placebo-controlled trial²⁸ with sitaxsentan (an endothelin A receptor selective antagonist) in PAH (the Sitaxsentan to Relieve Impaired Exercise-1 study), 178 NYHA functional class II, III and IV patients with either IPAH, PAH related to connective tissue disease, or PAH related to congenital systemic to pulmonary shunts, sitaxsentan improved exercise capacity (6MW distance) and functional class after 12 weeks of treatment. The treatment effects in the sitaxsentan groups were 35 m (p < 0.01) for the 100-mg dose and 33 m (p < 0.01) for the 300-mg dose. NYHA functional class and cardiopulmonary hemodynamics also improved. The incidence of liver function abnormalities was more favorable for the 100-mg dose. The most frequently reported clinical adverse events with sitaxsentan treatment were headache, peripheral edema, nausea, nasal congestion, and dizziness, and the most frequently reported laboratory adverse event was increased international normalized ratio or prothrombin time related to the effect of sitaxsentan on inhibition of CYP2C9 P450 enzyme, the principal hepatic enzyme involved in the metabolism of warfarin.

A second double-blind, placebo-controlled trial with sitaxsentan in PAH (the Sitaxsentan to Relieve Impaired Exercise-2 study²⁹) randomized 247 PAH patients (245 were treated) with IPAH, or PAH associated with connective tissue disease or congenital heart disease: placebo (n = 62); sitaxsentan, 50 mg (n = 62) or 100 mg (n = 61); or open-label bosentan (6MW tests, Borg dyspnea scores, and functional class assessments third-party blind; n = 60). The primary end point was change in 6MW distance from baseline to end of study. At week 18, patients treated with sitaxsentan, 100 mg, had an increased 6MW distance compared with the placebo group (31.4 m, p = 0.03), and an improved functional class (p = 0.04). The placebo-subtracted treatment effect for sitaxsentan, 50 mg, was 24.2 m (p = 0.07), and for open-label bosentan was 29.5 m (p = 0.05). The incidence of elevated hepatic transaminases (more than three times the upper limit of normal) was 6% for placebo; 5% for sitaxsentan, 50 mg; 3% for sitaxsentan, 100 mg; and 11% for bosentan. A new drug application is pending with the FDA.

An initial, phase two study³⁰ examined the efficacy and safety of four doses of ambrisentan, an oral endothelin type A receptor-selective antagonist, in patients with PAH. In this double-blind, dose-ranging study,³⁰ 64 patients with functional class II and III IPAH or PAH associated with connective tissue disease, anorexigen use, or HIV infection were randomized to receive 1, 2.5, 5, or 10 mg of ambrisentan qd for 12 weeks followed by 12 weeks of open-label ambrisentan. At 12 weeks, 6MW distance was increased (+ 36.1 m, p < 0.0001), with similar and statistically significant increases for each dose group (range, + 33.9 to + 38.1 m). Improvements were also observed in Borg dyspnea index, functional class, subject global assessment, PAPm (− 5.2 mm Hg, p < 0.0001), and cardiac index (+ 0.33 L/min/m², p < 0.0008). Adverse events were mild and unrelated to dose, including the incidence of elevated serum aminotransferase concentrations more than three times the upper limit of normal (3.1%). Two phase III clinical trials of ambrisentan in patients with PAH have recently been completed, and publication of the results is pending. Ambrisentan remains an investigational agent at this time.

Sildenafil is a potent and highly specific phosphodiesterase 5 inhibitor that has been previously approved for erectile dysfunction. Several reports³¹³²³³ of nonrandomized, single-center studies of PAH patients treated with long-term sildenafil suggested promise for sildenafil as a therapeutic agent. A double-blind, placebo-controlled study (the Sildenafil Use in Pulmonary Arterial Hypertension-1 study,³⁴) randomly assigned 278 patients with symptomatic PAH (either idiopathic or associated with connective tissue disease or with repaired congenital systemic-to-pulmonary shunts) to placebo or sildenafil (20, 40, or 80 mg po tid) for 12 weeks. 6MW distance increased from baseline in all sildenafil groups; mean placebo-corrected treatment effects were 45 m (+ 13.0%), 46 m (+ 13.3%), and 50 m (+ 14.7%) for 20, 40, and 80 mg of sildenafil, respectively (p < 0.001 for all comparisons). All sildenafil doses reduced the PAPm, improved the functional class, and were associated with side effects such as headache, flushing, epistaxis, dyspepsia, and diarrhea. The incidence of clinical worsening did not differ significantly between the patients treated with sildenafil and those treated with placebo. Among 222 patients completing 1 year of treatment with sildenafil monotherapy, the improvement from baseline at 1 year in the 6MW was 51 m. It should be noted that long-term data for sildenafil are available only at a dose of 80 mg po tid, while the dose approved by the FDA for the treatment of PAH is 20 mg tid.

The paradigm for treatment of PAH continues to advance rapidly. Multicenter randomized clinical trials (RCTs) have provided a basis for evidence-based practice. The treatment algorithm provided (Fig 1 ) attempts to summarize the current approach to therapy for PAH. The following brief overview, organized by functional class, is intended to facilitate clinical application of the algorithm. It should be noted that functional class is difficult to quantify, and may vary among patients and care providers. It may not always correlate with other indexes of disease severity, although it does correlate with outcome (in patients with IPAH). Accordingly, decisions regarding therapy should take into account a variety of variables, including but not limited to functional class. Treating physicians should also consider cardiopulmonary hemodynamics, 6MW distance, signs and symptoms of right-heart failure, side effect profile, and drug-drug interactions when making recommendations to individual patients. Cost may be a consideration in the choice of therapy.

Currently, the only therapies approved for functional class II patients are sildenafil and subcutaneous and IV treprostinil. Clinical trials with sitaxsentan^28,29 and ambrisentan³⁰ included functional class II patients, while an ongoing trial with bosentan is studying functional class II patients. Due to the ease of administration and relative efficacy, sildenafil may be the first choice for most functional class II patients. Enrollment into clinical trials is also encouraged.

There are now five drugs in three therapeutic classes approved by the FDA for the treatment of patients with functional class III PAH. Rational therapeutic decisions must be made based on the evidence outlined above, knowledge of an individual patient’s specific situation, clinical judgment, and patient preferences. Most experts now consider one of the two approved oral therapies (bosentan or sildenafil, listed in no order of preference) for patients with “early” functional class III PAH. In choosing between these agents, clinicians should consider relative toxicities. For example, patients with liver abnormalities, or inability to have liver tests monitored on a monthly basis might be better served by sildenafil. Patients with ocular disease or recurrent epistaxis might be better candidates for bosentan. If cost is a consideration, sildenafil tends to be less expensive. Patients with more advanced class III disease may require treatment with a prostanoid, such as IV epoprostenol or treprostinil, inhaled iloprost, or subcutaneous treprostinil. It is anticipated that we will soon have evidence regarding the use of add-on and combination therapy. Until additional evidence becomes available, add-on or combination therapy might be considered in the context of enrollment into clinical trials.

While all currently labeled therapies are approved for functional class IV patients, based on the quality of the evidence and the net risk/benefit profile, we strongly encourage IV epoprostenol as the treatment of choice for these most critically ill patients. IV epoprostenol has a rapid and predictable onset of action, and most experts are familiar with how to titrate this drug in the acute setting. Experience with IV treprostinil is accumulating; in some instances this may be a suitable alternative to IV epoprostenol. Recognizing that limited data are available on which to base treatment choices in patients with functional class IV symptoms, oral, subcutaneous, and inhaled agents should generally not be used as first-line therapy in this situation unless the patient refuses IV therapy or is believed not to be capable of managing the complex delivery system.

Recommendations regarding therapy obviously need to be applied in light of the individual patient’s specific situation (Table 4 ). The importance of a thorough diagnostic evaluation, looking for underlying causes and contributing factors, cannot be overemphasized. Educational efforts have contributed to improved recognition of PAH, facilitating earlier initiation of therapy. This should contribute to better clinical outcomes. Due to the complexity of the diagnostic evaluation required, and the treatment options available, it continues to be strongly recommended that consideration be given to referral of patients with PAH to a specialized center. Well-controlled clinical trials should continue to lead to further improvements in the treatment of this very challenging disease.