Meta-Analysis of Randomized Controlled Trials on Treatment of Pulmonary Arterial Hypertension

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1 Circulation Journal Official Journal of the Japanese Circulation Society Meta-Analysis of Randomized Controlled Trials on Treatment of Pulmonary Arterial Hypertension Bing He, BSc; Fengwen Zhang; Xueying Li, BSc; Chaoshu Tang; Guosheng Lin; Junbao Du, MD; Hongfang Jin, MD Background: The aim of the present meta-analysis was to evaluate the efficacy and safety of treating pulmonary arterial hypertension (PAH) with inhaled iloprost, oral bosentan and sildenafil. Methods and Results: The randomized controlled trials on the 3 drugs and placebo were retrieved from the databases MEDLINE, EMBASE, BIOSIS Previews and CNKI up to August In total 11 studies and 1,391 patients were selected. Compared with placebo, iloprost, bosentan and sildenafil reduced clinical worsening significantly (odds ratio [OR] =0.33, 95% confidence interval [CI] = , P< ), improved New York Heart Association/World Health Organization functional class (OR =2.81, 95%CI = , P< ), increased the 6-min walk test by m, reduced systolic pulmonary arterial pressure, mean pulmonary arterial pressure and pulmonary vascular resistance, increased the cardiac index by 0.40 L min 1 m 2 and increased the cardiac output by 0.53 L/min. The incidence of serious adverse events was similar in the medication groups and the placebo group (OR =1.09, 95%CI = , P=0.72). In terms of the clinical worsening and functional class amelioration, insignificant differences were found among iloprost, bosentan and sildenafil, but iloprost had the highest incidence of serious adverse events among the 3 drugs. Conclusions: Inhaled iloprost and oral bosentan and sildenafil are effective and safe in treating PAH. Key Words: Bosentan; Iloprost; Meta-analysis; Pulmonary arterial hypertension; Sildenafil Pulmonary arterial hypertension (PAH) is a chronic and severe fatal disease that can be secondary to the cardiac, pulmonary or systemic diseases or unexplained. Studies on PAH have been carried out for more than 100 years, but therapeutic measures remain limited. Current medication for PAH consists mainly of prostacyclins, endothelin receptor antagonists and phosphodiesterase type 5 (PDE-5) inhibitors. 1 Bosentan is a non-selective endothelin receptor antagonist that has been approved by the US Food and Drug Administration (FDA) for patients in World Health Organization (WHO) functional class III or IV to ameliorate exercise capacity and decrease the rate of clinical worsening. Sildenafil is a PDE-5 inhibitor, which has been approved by the US FDA for the treatment of PAH to improve exercise ability. 2 Iloprost is an inhaled prostacyclin drug that can act on the pulmonary blood vessels selectively and improve the hemodynamics of patients with PAH effectively; in addition, compared with traditional prostacyclin drugs, it has a longer halflife and can be administered by aerosol inhalation, avoiding the occurrence of infections, deep venous thrombosis, catheter displacement or pneumothorax resulting from previous iv medication. 3 These drugs can alleviate the symptoms in patients with PAH, and improve exercise capacity, hemodynamics and outcome. The clinical relevance of these effects, however, has been recently challenged, 4 6 mainly because of the limited amelioration of exercise capacity by medication, short duration and the small size of the individual studies, which have precluded any insight into the prognostic relevance of the treatments. Thus in the present study randomized controlled trails on treating PAH with inhaled iloprost and oral bosentan and sildenafil were collected to quantitatively analyze and compare the efficacy and safety of treating PAH using the 3 kinds of drugs, with a view to arrive at more credible conclusions and lay the theoretical foundation for Received December 6, 2009; revised manuscript received March 8, 2010; accepted March 12, 2010; released online June 1, 2010 Time for primary review: 30 days Department of Pediatrics (B.H.), Department of Cardiology (G.L.), Renmin Hospital of Wuhan University, Wuhan; Department of Pediatrics (F.Z., J.D., H.J.), Department of Statistics (X.L.), Peking University First Hospital, Beijing; Department of Physiology and Pathophysiology (C.T.), Peking University Health Sciences Center, Beijing; and Key Laboratory of Molecular Cardiology (C.T.), Ministry of Education, Beijing, China The first two authors contributed equally to this work (B.H., F.Z.). Mailing address: Junbao Du, MD or Hongfang Jin, MD, Department of Pediatrics, Peking University First Hospital, Beijing , P.R.China. junbaodu1@126.com or jinhongfang51@126.com ISSN doi: /circj.CJ All rights are reserved to the Japanese Circulation Society. For permissions, please cj@j-circ.or.jp

2 HE B et al. Table 1. Basic Characteristics of Included Trials Included trial Date of publication Quality rank No. subjects Trial group Control group Observation time (weeks) Etiological factors (%) Galiè et al A 54 Bosentan Placebo 16 PAH-ES (100) Channick et al A 32 Bosentan Placebo 12 IPAH (84), APAH (16) Galiè et al A 185 Bosentan* Placebo* 26 IPAH (61), APAH (35), other (4) Rubin et al B 213 Bosentan Placebo 16 IPAH (70), APAH (30) Galiè et al A 278 Sildenafil Placebo 12 IPAH (64), APAH (30) Olschewski et al B 203 Iloprost Placebo 12 IPAH (50), APAH (22), CTEPH (28) McLaughlin et al A 67 Iloprost** Placebo** 12 IPAH (55), APAH (45) Humbert et al B 33 Bosentan Placebo 16 IPAH (82), APAH (18) Hoeper et al C 40 Iloprost** Placebo** 12 IPAH (100) Singh et al B 20 Sildenafil Placebo 8 IPAH (59), PAH-ES (50) Simonneau et al A 267 Sildenafil Placebo 16 IPAH (79), APAH (21) *Eleven percent of the patients were treated with sildenafil simultaneously; **all patients were treated with bosentan simultaneously; all patients were treated with epoprostenol simultaneously. PAH-ES, Eisenmenger syndrome complicated with pulmonary arterial hypertension (PAH); IPAH, idiopathic PAH; APAH, associated with PAH; CTEPH, pulmonary hypertension due to chronic thrombotic and/or embolic disease. the treatment of PAH. Methods Study Inclusion Criteria The inclusion criteria were as follows: (1) any study on the treatment of pulmonary hypertension using iloprost, bosentan and sildenafil that has been or will be published; (2) randomized controlled trials; and (3) patients definitely diagnosed as having PAH as study subjects. According to the clinical classification of PAH by the ACCF/AHA 2009 Conference, 7 the categories of PAH were as follows: (1) idiopathic PAH; (2) familial PAH; (3) associated with PAH (ie, connective tissue disorders, congenital systemic-to-pulmonary shunts, portal hypertension, HIV infection; drugs and toxins, and others [thyroid disorders, glycogen storage disease, Gaucher s disease, hereditary hemorrhagic telangiectasia, hemoglobinopathies, chronic myeloproliferative disorders and splenectomy]); (4) associated with significant venous or capillary involvement: pulmonary veno-occlusive disease, pulmonary capillary hemangiomatosis; and (5) persistent pulmonary hypertension of the newborn. Diagnosis of PAH was made referring to the expert consensus on diagnosis and treatment in PAH. 7 Study Exclusion Criteria The exclusion criteria were as follows: (1) literatures with small sample size and incomprehensive information; and (2) any of the following items: persistent PAH of the newborn in the classification of PAH; therapies other than inhaled iloprost and oral bosentan and sildenafil treatment; and animal experimental studies on the treatment of PAH. Document Retrieval Retrieval of Electronic Records The searchable database includes MEDLINE, EMBASE, BIOSIS Previews and CNKI up to August Manual retrieval, including retrieving the compilation of academic conference articles and dissertations, was used to collect the data related to medication of PAH as comprehensively as possible. Retrieval Strategies The databases were searched by 2 professional co-workers using the search term bosentan or sildenafil or iloprost and pulmonary hypertension. Study Quality Evaluation After retrieval the studies were checked by 2 reviewers in accordance with inclusion and exclusion criteria, to conduct full-text searching for studies with abstracts insufficiently expressed, and to determine whether to include a study after reading through the full text. The included studies were subjected to quality evaluation in line with the Juni scale to see: (1) if the randomized approach was correct; (2) if allocation concealment had been realized and if the method was correct; (3) if the blind method had been adopted; and (4) if there were any lost case or withdrawal and, if so, whether the reasons had been clearly elucidated or the intention-totreat analytical method had been adopted. If these 4 criteria of quality evaluation were fully met, the possibility of bias in that study was regarded to be the smallest (grade A); if any 1 or several criteria of quality evaluation were partially met, the possibility of bias in that study was intermediate (grade B); if any or several criteria of quality evaluation were completely not satisfied, the possibility of bias in that study was high (grade C). Evaluation Indicators for Efficacy and Safety The situation of clinical worsening, New York Heart Assocation (NYHA)/WHO functional class, 6-min walk test (6MWT), and hemodynamic parameters including systolic pulmonary arterial pressure, mean pulmonary arterial pressure, pulmonary vascular resistance, cardiac output and cardiac index, were applied to evaluate the efficacy of drugs. The safety of drugs was determined by the serious adverse events that were considered to be related to the studied medication as indicated in the original articles. Statistical Analysis The selected research studies were analyzed using the statistical software Revman 4.2 available on international evidencebased medicine cooperative network, and allocated into measurement data and count data based on the types of data. The Q test was conducted on the research effect size to evaluate heterogeneity. When the research effect size was homogeneous, count data were analyzed using a fixed effect model (Peto s method). P<0.05 indicated a statistically significant difference. Combined odds ratio (OR) and 95% confidence interval (CI) were recorded. Measurement data were analyzed using the weighted mean difference and 95%CI. If the

3 Treatment for PAH 0.0 SE(log OR) OR (fixed) Figure 1. Funnel plot of randomized controlled trials. X-axis represents effect estimate for each study under the outcome. Y-axis represents standard error (log(effect estimate)). Each dot represents a study and the distance between each dot and the vertical line suggests bias in each study. Because the whole funnel composed by all the dots was not completely symmetric, publication bias may exist. SE, standard error; OR, odds ratio. Figure 2. Clinical worsening: comparison of drugs and placebo in treating pulmonary arterial hypertension, excluding nonevent trials (P=0.52). No existence of heterogeneity was found. Fixed effect model for combined effect size was adopted. CI, confidence interval; OR, odds ratio. research effect size was heterogeneous, the random effect model for combined effect size was applied for estimation. Results Study Evaluation A total of 1,894 studies were retrieved using the aforementioned retrieval methods, among which 11 meeting the inclusion criteria were screened (Table 1). Among them, 3 presented results on the controlled treatment of PAH with inhaled iloprost and placebo, 3 involved controlled trials on Table 2. Clinical Worsening in PAH vs Drug Treatment Drug Clinical worsening No clinical worsening Total (n) Bosentan Sildenafil Iloprost Total χ2 =0.227, P= Abbreviation see in Table 1.

4 HE B et al. Figure 3. Status of functional class amelioration: comparison of drugs and placebo in treating pulmonary arterial hypertension, excluding non-event trials (P=0.07). No existence of heterogeneity was found. Fixed effect model for combined effect size was adopted. CI, confidence interval; OR, odds ratio. Table 3. Functional Class Amelioration in PAH vs Drug Treatment Drugs Improvement of functional class No improvement of functional class Total (n) Bosentan Sildenafil Iloprost Total χ2 =3.812, P= Abbreviation see in Table 1. sildenafil and placebo and the other 5 reported controlled trials on bosentan and placebo. In total, 1,391 PAH patients were included, consisting of 822 patients in the medication group and 569 patients in the placebo group. Among the 11 included studies, 6 met grade A criteria of quality evaluation on the Juni scale, 4 met grade B and 1 met grade C. The inverted funnel plot indicates that there may be publication bias (Figure 1). Efficacy Evaluation for PAH Medication Clinical Worsening Clinical worsening refers to the need for hospitalization due to the emergence of right heart dysfunction or progressive increase of pulmonary arterial pressure and the necessity of withdrawal from the trial due to the need to alter medication, or the occurrence of inter-atrial fistulization, lung transplantation or even death because the clinical symptoms were not alleviated or had become aggravated. Among the 1,391 subjects in the 11 trials, 119 (8.55%) developed clinical worsening, consisting of 40 in the medication group (4.87%) and 79 in the placebo group (13.88%). The clinical worsening incidence was significantly lower in the medication group than the placebo group (OR=0.33, 95%CI= , P< ). Subgroup analysis on the 3 kinds of drugs is given in Figure 2. This shows that the clinical worsening incidence in patients treated with bosentan and sildenafil was significantly lower than that in patients treated with placebo. The clinical worsening incidence was also lower in patients treated with iloprost than in the placebo group, but the difference was not statistically significant. As shown in Table 2, there was a non-significant difference for the emergence of clinical worsening among the 3 kinds of drugs (χ2 =0.227, P=0.893), indicating that bosentan, sildenafil and iloprost were not significantly different in improving clinical worsening. NYHA/WHO Functional Class Among the 1,064 subjects in the 8 trials, the functional class was ameliorated by at least 1 grade in 248 subjects (23.31%), including 199 (30.2%) in the medication group and 49 (12.1%) in the placebo group The status of functional class amelioration was superior in the medication group to the placebo group (OR= 2.81, 95%CI= , P< ; Figure 3). Subgroup analysis on the 3 kinds of drugs showed that the status of functional class amelioration was superior in patients treated with bosentan, sildenafil or iloprost to those treated in the placebo group. As shown in Table 3, the status of functional class amelioration among the 3 drugs was not statistically significant (χ2 =3.812, P=0.149), indicating that bosentan, sildenafil and iloprost were not significantly different in ameliorating functional class. 6MWT The 6MWT alone or in combination was the primary endpoint in 9 studies and the secondary endpoint in another 2 studies. One of the 11 trials showed that the 6MWT of patients was decreased after medication, but that of patients

5 Treatment for PAH Figure 4. Emergence of serious adverse events in pulmonary arterial hypertension patients treated by drugs and placebo, excluding non-event trials (P=0.99), with no existence of heterogeneity. Fixed effect model for combined effect size was adopted. CI, confidence interval; OR, odds ratio. treated with placebo was increased. 16 Another trial showed that the 6MWT of patients in both the placebo and medication groups was increased, but that the increase was higher in the placebo group. 15 In the other 9 trials the increase in the 6MWT of patients in the medication group was higher than that of the placebo group. As the effect size, the weighted mean difference was applied to calculate the 95%CI of the 2 mean differences. The 6MWT of patients was significantly elevated after medication compared to that after placebo treatment (95%CI= , P< ). Subgroup analysis of different kinds of drugs showed that the 6MWT was increased by an average of m in the bosentan treatment group compared to the placebo treatment group, by an average of m in the sildenafil treatment group compared to the placebo treatment group and by an average of m in the iloprost treatment group compared to the placebo treatment group, suggesting that the 3 kinds of drugs could significantly increase 6MWT and that the choice of drugs had no effect on the result. Hemodynamic Parameters Five trials evaluating the changes in systolic pulmonary arterial pressure showed that medication could reduce systolic pulmonary arterial pressure. 9,10,13,17,18 On testing for heterogeneity, P=0.13 and the fixed effect model for combined effect size was adopted. Pulmonary arterial systolic pressure fell by an average of 4.64 mmhg in the medication group compared to the placebo group (95%CI= 6.02 to 3.26, P< ). Four trials showed that the mean pulmonary arterial pressure was decreased in the medication group. 8,12,14,15 The mean pulmonary arterial pressure was reduced by an average of 4.05 mmhg in the medication group compared to the placebo treatment group (95%CI= 4.54 to 3.56, P< ). In 7 trials the changes in pulmonary vascular resistance were evaluated. On testing for heterogeneity P=0.0004, indicating the existence of heterogeneity, and therefore the random effect model for combined effect size was adopted. Compared with placebo, drugs significantly reduced pulmonary vascular resistance in patients with PAH by an average of dyn s cm 5 (95%CI= to , P< ). In 4 trials the changes in the cardiac index were evaluated. 9,10,12,15 On testing for heterogeneity P< , indicating the existence of heterogeneity and therefore the random effect model for combined effect size was adopted. The cardiac index was increased by an average of 0.40 L min 1 m 2 in the medication group compared to the placebo group (95%CI= , P=0.007). In 3 trials evaluating the changes in cardiac output, the existence of heterogeneity was confirmed (P= 0.01), and the random effect model for combined effect size was adopted. Cardiac output was increased by an average of 0.53 L/min in the medication group compared to the placebo group (95%CI= , P=0.02). Safety Among the 1,391 patients including those receiving medication (n=822) and placebo (n=569), 94 (6.76%) reported serious adverse events. The incidence of serious adverse events had a higher trend in the medication group than the placebo group, but the difference was not statistically significant (Figure 4). Five of the 11 trials on bosentan showed that 31 (6%) of the included 517 patients suffered from serious adverse events. 8 11,15 In 1 trial adverse events led to premature discontinuation of the study medication, but the researchers did not refer to the intensity of the adverse events. 11 Three trials on sildenafil included 564 subjects, among whom 7 (1.24%) developed serious adverse events. 12,17,18 The other 3 trials on iloprost included 310 sub-

6 HE B et al. Table 4. Post-Treatment Serious Adverse Events vs Drug Drugs Serious adverse events jects, among whom 56 (18.06%) developed serious adverse events. 13,14,16 The results showed that inhaled iloprost and oral bosentan and sildenafil were safe for the treatment of PAH; comparison of the 3 kinds of drugs with placebo showed that the incidence of serious adverse events was the lowest after oral administration of bosentan. As shown in Table 4, the emergence of serious adverse events among the 3 kinds of drugs was statistically significantly different (χ2 =57.134, P<0.0001), indicating that the incidence of serious adverse events after treatment by sildenafil was lower than that after treatment by bosentan and iloprost. In conclusion, the incidence of serious adverse events was highest after treatment by iloprost. Discussion No serious adverse events Total (n) Bosentan Sildenafil Iloprost Total χ2 =57.134, P< Iloprost is a prostacyclin analog, and aerosol inhalation of iloprost can selectively dilate pulmonary blood vessels and reduce pulmonary arterial pressure; and it also has anti-proliferative and anti-thrombotic effects, 13 thus alleviating the clinical symptoms in patients with PAH. Bosentan is a nonselective endothelin receptor antagonist, which can resist activities of endothelin receptor type A and type B and dilate pulmonary blood vessels, thus improving exercise capacity, hemodynamics and the situation of clinical worsening in patients with PAH. 19 Sildenafil is a highly selective PDE-5 inhibitor. It can enhance the concentration of cyclic guanosine monophosphate of pulmonary vascular smooth muscle cells through inhibiting PDE-5 and promote the function of endogenous nitric oxide. 20,21 In addition, it has the effect of inhibiting vascular smooth muscle cell proliferation, 22 alleviating pulmonary vascular remodeling and thus attenuating PAH effectively. The present study investigated the randomized controlled trials of inhaled iloprost and oral bosentan and sildenafil for treatment of PAH, to assess the efficacy and safety of the 3 kinds of drugs in treating patients with PAH. With regard to clinical condition progression, it can be seen that 13.88% of the patients in the placebo group developed clinical worsening during treatment; although medication could alleviate clinical worsening in patients, 4.87% of patients in the medication group developed clinical worsening, suggesting that PAH is really an intractable disease endangering the life of patients. According to the subgroup analysis of different drugs, comparison of the 3 kinds of drugs with placebo showed that bosentan and sildenafil were more effective than iloprost in ameliorating clinical worsening, but comparison among the 3 kinds of drugs showed no differences in the outcome, which might be related to the smaller sample size in the iloprost group (n=154) compared to that in bosentan (n=317) and sildenafil (n=354) groups. The results with respect to serious adverse events are more variable, which might be related to the combined therapy in some patients, or the distinction in evaluation criteria of different research centers on serious adverse events. Although the incidence of serious adverse events was higher in the medication group than the placebo group, the reasons why the patients in the placebo group developed serious adverse events were not clear. In the 5 trials conducted on bosentan, the most frequent serious adverse events were biliary colic, cholelithiasis, syncope, angina pectoris, liver function abnormalities and sinus tachycardia in the bosentan group and acute cholecystitis, upper abdominal pain, respiratory failure, right ventricular failure and syncope in the placebo group. 8 11,15 In the 3 trials conducted on sildenafil, the most frequent serious adverse events were hypoxia, hypotension and left ventricular dysfunction in the sildenafil group and tachycardia, hypoxia and dyspnea in the placebo group. 12,17,18 And in the 3 trials conducted on iloprost, the most frequent serious adverse events were syncope, tachycardia, dyspnea, right ventricular failure and edema in the iloprost group and right-heart failure in the placebo group. 13,14,16 To sum up, compared with placebo, inhaled iloprost and orally administered bosentan and sildenafil can significantly alleviate clinical worsening in patients with PAH, ameliorate the functional class and hemodynamics, increase 6MWT but not elevate the incidence of serious adverse events, suggesting that iloprost, bosentan and sildenafil are safe and effective in treating PAH. Further comparison of the efficacy and safety of the 3 kinds of drugs has found that alleviation of clinical worsening and amelioration of the functional class in patients with PAH does not differ. These date suggest that the results have not been driven by 1 of the 3 drugs. The incidence of serious adverse events is the highest in patients given iloprost. It should be noted that in 1 study 28 patients (27.7%) in the iloprost group and 25 patients (24.5%) in the placebo group developed serious adverse events, but the author did not indicate whether the events were related to the studied medication or not. 13 The previous reported meta-analysis suggested an improvement of survival in the patients treated with the targeted therapies including endothelin receptor antagonists, PDE-5 inhibitors and prostanoids approved for PAH. 23 Despite these results, the current treatment strategy remains inadequate because the mortality rate continues to be high and the functional and hemodynamic impairments are still extensive in many patients. Further efforts are required to explore new strategies. Given the availability of medication targeting different pathologic processes, combination therapy is an attractive theoretical option. In a randomized, multicentre, doubleblind and placebo-controlled study of combination therapy, patients started treatment with epoprostenol and were randomized to placebo or bosentan for 16 weeks. 15 That study failed to demonstrate the benefits of combination therapy. In a randomized and double-blind study, 67 patients on stable monotherapy with bosentan received combination therapy with the addition of either inhaled iloprost or placebo. 14 After 12 weeks post-inhalation 6MWT improved by 30 m in the iloprost group but 4 m in the placebo group. There were also improvements in NYHA functional class, time to clinical worsening and post-inhalation mean pulmonary arterial pressure and pulmonary vascular resistance. In another study with a similar design, however, 6MWT improved by 1 m in the placebo group but decreased by 9 m in the iloprost group. 16 None of the secondary endpoints, including functional class, peak oxygen uptake and time to clinical worsening differed between the groups. Recently, in a randomized, multicentre, double-blind and placebo-controlled study of combination

7 Treatment for PAH therapy, 267 patients started treatment with epoprostenol and were randomized to placebo or sildenafil for 16 weeks. 18 Patients treated with sildenafil experienced a placebo-adjusted improvement in 6MWT of 28.8 m, as well as improvements in mean pulmonary arterial pressure, cardiac output and time to clinical worsening. The present meta-analysis did not compare combination therapy and monotherapy because of the different designs of the 11 studies. It is necessary to design more trials to adequately study the safety and efficacy of combination therapy. There were some limitations to the present study. Some trials adopted combination therapy, 10,14 16,18 among which 2 used drugs in addition to iloprost, bosentan and sildenafil; 15,18 and 1 trial included patients with chronic thromboembolic PAH. 13 The observation time in the majority of trials was short (commonly weeks), apart from the 1 lasting for 24 weeks. In addition, the inverted funnel plot indicated the existence of publication bias, because trials with negative results are more difficult to publish and the difference in baseline data of the trial and control groups may lead to publication bias. Further design of randomized controlled trials on combination therapy or new PAH medication or evaluation of the long-term efficacy of medication for PAH is still necessary. References 1. Humbert M, Sitbon O, Simonneau G. Treatment of pulmonary arterial hypertension. N Engl J Med 2004; 351: Torres F. Systematic review of randomised, double-blind clinical trials of oral agents conducted in patients with pulmonary arterial hypertension. Int J Clin Pract 2007; 61: Krug S, Sablotzki A, Hammerschmidt S, Wirtz H, Seyfarth HJ. Inhaled iloprost for the control of pulmonary hypertension. Vasc Health Risk Manag 2009; 5: Rich S. The value of approved therapies for pulmonary arterial hypertension. Am Heart J 2007; 153: Farber HW. The status of pulmonary arterial hypertension in Circulation 2008; 117: Ghofrani HA, Wilkins MW, Rich S. Uncertainties in the diagnosis and treatment of pulmonary arterial hypertension. Circulation 2008; 118: McLaughlin VV, Archer SL, Badesch DB, Barst RJ, Farber HW, Lindner JR, et al. ACCF/AHA 2009 expert consensus document on pulmonary hypertension. J Am Coll Cardiol 2009; 53: Galiè N, Beghetti M, Gatzoulis MA, Granton J, Berger RM, Lauer A, et al. Bosentan therapy in patients with Eisenmenger syndrome: A multicenter, double-blind, randomized, placebo-controlled study. Circulation 2006; 114: Channick RN, Simonneau G, Sitbon O, Robbins IM, Frost A, Tapson VF, et al. Effects of the dual endothelin-receptor antagonist bosentan in patients with pulmonary hypertension: A randomised placebo controlled study. Lancet 2001; 358: Galiè N, Rubin LJ, Hoeper M, Jansa P, Al-Hiti H, Meyer G, et al. Treatment of patients with mildly symptomatic pulmonary arterial hypertension with bosentan (EARLY study): A double-blind, randomised controlled trial. Lancet 2008; 371: Rubin LJ, Badesch DB, Barst RJ, Galie N, Black CM, Keogh A, et al. Bosentan therapy for pulmonary arterial hypertension. N Engl J Med 2002; 346: Galiè N, Ghofrani HA, Torbicki A, Barst RJ, Rubin LJ, Badesch D, et al. Sildenafil citrate therapy for pulmonary arterial hypertension. N Engl J Med 2005; 353: Olschewski H, Simonneau G, Galiè N, Higenbottam T, Naeije R, Rubin LJ, et al. Inhaled iloprost for severe pulmonary hypertension. N Engl J Med 2002; 347: McLaughlin VV, Oudiz RJ, Frost A, Tapson VF, Murali S, Channick RN, et al. Randomized study of adding inhaled iloprost to existing bosentan in pulmonary arterial hypertension. Am J Respir Crit Care Med 2006; 174: Humbert M, Barst RJ, Robbins IM, Channick RN, Galiè N, Boonstra A, et al. Combination of bosentan with epoprostenol in pulmonary arterial hypertension: BREATHE-2. Eur Respir J 2004; 24: Hoeper MM, Leuchte H, Halank M, Wilkens H, Meyer FJ, Seyfarth HJ, et al. Combining inhaled iloprost with bosentan in patients with idiopathic pulmonary arterial hypertension. Eur Respir J 2006; 28: Singh TP, Rohit M, Grover A, Malhotra S, Vijavergiya R. A randomized, placebo-controlled, double-blind, crossover study to evaluate the efficacy of oral sildenafil therapy in severe pulmonary artery hypertension. Am Heart J 2006; 151: 851.e1 851.e Simonneau G, Rubin LJ, Galiè N, Barst RJ, Fleming TR, Frost AE, et al. Addition of sildenafil to long-term intravenous epoprostenol therapy in patients with pulmonary arterial hypertension: A randomized trial. Ann Intern Med 2008; 149: Akagi S, Matsubara H, Miyaji K, Ikeda E, Dan K, Tokunaga N, et al. Additional effects of bosentan in patients with idiopathic pulmonary arterial hypertension already treated with high-dose epoprostenol. Circ J 2008; 72: Corbin JD, Francis SH. Cyclic GMP phosphodiesterase-5: Target of sildenafil. J Biol Chem 1999; 274: Sakuma M, Demachi J, Nawata J, Suzuki J, Takahashi T, Shirato K. Long-term epoprostenol therapy in pulmonary artery hypertension. Circ J 2009; 73: Tantini B, Manes A, Fiumana E, Pignatti C, Guarnieri C, Zannoli R, et al. Antiproliferative effect of sildenafil on human pulmonary artery smooth muscle cells. Basic Res Cardiol 2005; 100: Galiè N, Manes A, Negro L, Palazzini M, Letizia M, Branzi A. A meta-analysis of randomized controlled trials in pulmonary arterial hypertension. Eur Heart J 2009; 30: