IMPAHCT: A randomized phase 2b/3 study of inhaled imatinib for pulmonary arterial hypertension.

AV-101 (imatinib) powder for inhalation, an investigational dry powder inhaled formulation of imatinib designed to target the underlying pathobiology of pulmonary arterial hypertension, was generally well tolerated in healthy adults in a phase 1 single and multiple ascending dose study. Inhaled Imatinib Pulmonary Arterial Hypertension Clinical Trial (IMPAHCT; NCT05036135) is a phase 2b/3, randomized, double-blind, placebo-controlled, dose-ranging, and confirmatory study. IMPAHCT is designed to identify an optimal AV-101 dose (phase 2b primary endpoint: pulmonary vascular resistance) and assess the efficacy (phase 3 primary endpoint: 6-min walk distance), safety, and tolerability of AV-101 dose levels in subjects with pulmonary arterial hypertension using background therapies. The study has an operationally seamless, adaptive design allowing for continuous recruitment. It includes three parts; subjects enrolled in Part 1 (phase 2b dose-response portion) or Part 2 (phase 3 intermediate portion) will be randomized 1:1:1:1 to 10, 35, 70 mg AV-101, or placebo (twice daily), respectively. Subjects enrolled in Part 3 (phase 3 optimal dose portion) will be randomized 1:1 to the optimal dose of AV-101 and placebo (twice daily), respectively. All study parts include a screening period, a 24-week treatment period, and a 30-day safety follow-up period; the total duration is ∼32 weeks. Participation is possible in only one study part. IMPAHCT has the potential to advance therapies for patients with pulmonary arterial hypertension by assessing the efficacy and safety of a novel investigational drug-device combination (AV-101) using an improved study design that has the potential to save 6-12 months of development time. ClinicalTrials.gov Identifier: NCT05036135.

Epidemiology, healthcare utilization, and related costs among patients with IPF: results from a German claims database analysis.

BACKGROUND: Idiopathic pulmonary fibrosis (IPF) is a progressive form of fibrosing interstitial pneumonia with poor survival. This study provides insight into the epidemiology, cost, and disease course of IPF in Germany. METHODS: A cohort of incident patients with IPF (n = 1737) was identified from German claims data (2014-2019). Incidence and prevalence rates were calculated and adjusted for age differences compared with the overall German population. All-cause and IPF-related healthcare resource utilization as well as associated costs were evaluated per observed person-year (PY) following the initial IPF diagnosis. Finally, Kaplan-Meier analyses were performed to assess time from initial diagnosis to disease deterioration (using three proxy measures: non-elective hospitalization, IPF-related hospitalization, long-term oxygen therapy [LTOT]); antifibrotic therapy initiation; and all-cause death. RESULTS: The cumulative incidence of IPF was estimated at 10.7 per 100,000 individuals in 2016, 10.9 in 2017, 10.5 in 2018, and 9.6 in 2019. The point prevalence rates per 100,000 individuals for the respective years were 21.7, 23.5, 24.1, and 24.1. On average, ≥ 14 physician visits and nearly two hospitalizations per PY were observed after the initial IPF diagnosis. Of total all-cause direct costs (€15,721/PY), 55.7% (€8754/PY) were due to hospitalizations and 29.1% (€4572/PY) were due to medication. Medication accounted for 49.4% (€1470/PY) and hospitalizations for 34.8% (€1034/PY) of total IPF-related direct costs (€2973/PY). Within 2 years of the initial IPF diagnosis (23.6 months), 25% of patients died. Within 5 years of diagnosis, 53.1% of patients had initiated LTOT; only 11.6% were treated with antifibrotic agents. The median time from the initial diagnosis to the first non-elective hospitalization was 5.5 months. CONCLUSION: The incidence and prevalence of IPF in Germany are at the higher end of the range reported in the literature. The main driver for all-cause cost was hospitalization. IPF-related costs were mainly driven by medication, with antifibrotic agents accounting for around one-third of the total medication costs even if not frequently prescribed. Most patients with IPF do not receive pharmacological treatment, highlighting the existing unmet medical need for effective and well-tolerated therapies.

Idiopathic pulmonary fibrosis: Physician and patient perspectives on the pathway to care from symptom recognition to diagnosis and disease burden.

BACKGROUND AND OBJECTIVE: Idiopathic pulmonary fibrosis (IPF) is a chronic progressive disease that requires ongoing care and is associated with considerable socioeconomic burden. We evaluated the IPF care pathway from symptom recognition to treatment. We describe the impact of IPF on healthcare resource use (HCRU), quality of life (QoL) and work impairment, and report differences in patient and physician perspectives using real-world data from France, Germany, Japan and the United States. METHODS: Quantitative, point-in-time data were collected as part of the Adelphi IPF II Disease Specific Programme™. Physician-reported data (patient demographics, medical history, diagnoses, treatment) were matched to patient-reported data (HCRU, QoL, work impairment). HCRU was measured as physician visits and hospitalizations. QoL and work impairment were measured using the EuroQol-5 Dimensions (EQ-5D) and Work Productivity and Activity Impairment questionnaires. RESULTS: Overall, 244 physicians reported data on 1249 patients, 739 of whom self-reported data. Diagnostic delays of 0.8 (Germany) to 2.0 (Japan) years after symptom onset were reported; treatment initiation was further delayed. In all countries, patients more often reported symptoms in the survey than did their physicians. On average, patients underwent 7-10 clinical tests before diagnosis. Antifibrotic use increased from 57% (2016) to 69% (2019); only 50% of patients with moderate/severe IPF were satisfied with their treatment. The 12-month hospitalization rates were 24% (Japan) to 64% (United States). Patients reported low QoL (mean EQ-5D visual analogue scale: 61.7/100). CONCLUSION: Patients with IPF experience considerable diagnostic and treatment delays. More effective therapies and management are needed to reduce the disease burden.

Global incidence and prevalence of idiopathic pulmonary fibrosis.

BACKGROUND: Idiopathic pulmonary fibrosis (IPF) is a progressive debilitating lung disease with considerable morbidity. Heterogeneity in epidemiologic studies means the full impact of the disease is unclear. METHODS: A targeted literature search for population-based, observational studies reporting incidence and/or prevalence of IPF from January 2009 to April 2020 was conducted. Identified studies were aggregated by country. For countries with multiple publications, a weighted average was determined. Incidence and prevalence data were adjusted for between-study differences where possible. The final model included adjusted estimates of incidence and prevalence per 10,000 of the population with 95% confidence intervals. As prevalence estimates vary depending on the definitions used, estimates were based on a specific case definition of IPF. RESULTS: Overall, 22 studies covering 12 countries met the inclusion criteria, with 15 reporting incidence and 18 reporting prevalence estimates. The adjusted incidence estimates (per 10,000 of the population) ranged from 0.35 to 1.30 in Asia-Pacific countries, 0.09 to 0.49 in Europe, and 0.75 to 0.93 in North America. Unadjusted and adjusted incidence estimates were consistent. The adjusted prevalence estimates ranged from 0.57 to 4.51 in Asia-Pacific countries, 0.33 to 2.51 in Europe, and 2.40 to 2.98 in North America. South Korea had the highest incidence and prevalence estimates. When prevalence estimates were compared to country-specific rare disease thresholds, IPF met the definition of a rare disease in all countries except South Korea. There were notable geographic gaps for IPF epidemiologic data. CONCLUSIONS: Due to differences in study methodologies, there is worldwide variability in the reported incidence and prevalence of IPF. Based on the countries included in our analysis, we estimated the adjusted incidence and prevalence of IPF to be in the range of 0.09-1.30 and 0.33-4.51 per 10,000 persons, respectively. According to these prevalence estimates, IPF remains a rare disease. For consistency, future epidemiologic studies of IPF should take age, sex, smoking status, and the specificity of case definitions into consideration.

Initial combination therapy of ambrisentan and tadalafil in connective tissue disease-associated pulmonary arterial hypertension (CTD-PAH) in the modified intention-to-treat population of the AMBITION study: post hoc analysis.

OBJECTIVES: To evaluate initial combination therapy with ambrisentan plus tadalafil (COMB) compared with monotherapy of either agent (MONO), and the utility of baseline characteristics and risk stratification in predicting outcomes, in patients with connective tissue disease-associated pulmonary arterial hypertension (CTD-PAH) and the systemic sclerosis (SSc)-pulmonary arterial hypertension (PAH) subpopulation. METHODS: This post hoc analysis of the Ambrisentan and Tadalafil in Patients with Pulmonary Arterial Hypertension (AMBITION) study included patients with CTD-PAH from the modified intention-to-treat population. Time to clinical failure (TtCF) was assessed by baseline characteristics, treatment assignment and risk group (low, intermediate and high) at baseline and week 16. TtCF was compared between groups using Kaplan-Meier curves and Cox proportional hazards regression modelling. RESULTS: The analysis included 216 patients (COMB, n=117; MONO, n=99). The risk of clinical failure was lower with COMB versus MONO (risk reduction: CTD-PAH 51.7%, SSc-PAH 53.7%), particularly in patients with haemodynamic parameters characteristic of typical PAH without features of left heart disease and/or restrictive lung disease at baseline. The risk of clinical failure was lower with COMB versus MONO in the baseline low-risk group (HR not calculated due to no events in COMB), baseline intermediate-risk group (HR 0.519, 95% CI 0.297 to 0.905) and in the week 16 low-risk group (HR 0.069, 95% CI 0.009 to 0.548). CONCLUSIONS: The benefit of COMB over MONO was demonstrated in patients with CTD-PAH, particularly in those with typical PAH haemodynamic characteristics at baseline. COMB is appropriate for patients categorised as low risk and intermediate risk at baseline and low risk at follow-up. TRIAL REGISTRATION NUMBER: NCT01178073.

Patients with pulmonary arterial hypertension with and without cardiovascular risk factors: Results from the AMBITION trial.

BACKGROUND: The purpose of this study was to compare patients with pulmonary arterial hypertension enrolled in the AMBITION trial with (excluded from the primary analysis set [ex-primary analysis set]) and without (primary analysis set) multiple risk factors for left ventricular diastolic dysfunction. METHODS: Treatment-naive patients with pulmonary arterial hypertension were randomized to once-daily ambrisentan and tadalafil combination therapy, ambrisentan monotherapy, or tadalafil monotherapy. The primary end point was time from randomization to first adjudicated clinical failure event. RESULTS: Primary analysis set patients (n = 500), compared with ex-primary analysis set patients (n = 105), were younger (mean, 54.4 vs 62.1 years) with greater baseline 6-minute walk distance (median, 363.7 vs 330.5 meters) and fewer comorbidities (e.g., hypertension and diabetes). Treatment effects of initial combination therapy vs pooled monotherapy were directionally the same for both populations, albeit of a lower magnitude for ex-primary analysis set patients. Initial combination therapy reduced the risk of clinical failure compared with pooled monotherapy in primary analysis set patients (hazard ratio, 0.50; 95% confidence interval, 0.35-0.72), whereas the effect was less clear in ex-primary analysis set patients (hazard ratio, 0.70; 95% confidence interval, 0.35-1.37). Overall, primary analysis set patients had fewer clinical failure events (25% vs 33%), higher rates of satisfactory clinical response (34% vs 24%), and lower rates of permanent study drug withdrawal due to adverse events (16% vs 31%) than ex-primary analysis set patients. CONCLUSIONS: Efficacy of initial combination therapy vs pooled monotherapy was directionally similar for primary analysis set and ex-primary analysis set patients. However, ex-primary analysis set patients (with multiple risk factors for left ventricular diastolic dysfunction) experienced higher rates of clinical failure events and the response to combination therapy vs monotherapy was attenuated. Tolerability was better in primary analysis set than ex-primary analysis set patients.

Clinical outcomes stratified by baseline functional class after initial combination therapy for pulmonary arterial hypertension.

BACKGROUND: Initial combination therapy with ambrisentan and tadalafil reduced the risk of clinical failure events for treatment-naïve participants with pulmonary arterial hypertension (PAH) as compared to monotherapy. Previous studies in PAH have demonstrated greater treatment benefits in more symptomatic participants. METHODS: AMBITION was an event-driven, double-blind study in which participants were randomized 2:1:1 to once-daily initial combination therapy with ambrisentan 10 mg plus tadalafil 40 mg, ambrisentan 10 mg plus placebo, or tadalafil 40 mg plus placebo. In this pre-specified subgroup analysis, we compared the efficacy data between those with functional class (FC) II vs. FC III symptoms at baseline. RESULTS: This analysis included 500 participants in the previously defined primary analysis set (n = 155 FC II, n = 345 FC III). Comparing combination therapy to pooled monotherapy, the risk of clinical failure events was reduced by 79% (hazard ratio, 0.21 [95% confidence interval: 0.071, 0.63]) for FC II patients and 42% (hazard ratio, 0.58 [95% confidence interval: 0.39, 0.86]) for FC III patients. In a post-hoc analysis, the risk of first hospitalization for worsening PAH was also reduced by combination therapy, particularly for FC II patients (0 combination vs. 11 [14%] pooled monotherapy). Adverse events were frequent but comparable between the subgroups. CONCLUSIONS: Treatment benefit from initial combination therapy appeared at least as great for FC II as for FC III participants. Hospitalizations for worsening PAH were not observed in FC II participants assigned to combination. The present data support an initial combination strategy for newly diagnosed patients even when symptoms are less severe. Funded by Gilead Sciences, Inc. and GlaxoSmithKline; AMBITION ClinicalTrials.gov number, NCT01178073.

Initial combination therapy with ambrisentan + tadalafil on pulmonary arterial hypertension‒related hospitalization in the AMBITION trial.

BACKGROUND: In the randomized, double-blind, event-driven AMBITION study, initial combination therapy with ambrisentan and tadalafil was associated with a 50% reduction in risk of clinical failure (first occurrence of all-cause death, hospitalization for worsening pulmonary arterial hypertension [PAH], disease progression, or unsatisfactory long-term clinical response) vs pooled monotherapy. These results were primarily driven by a reduction in PAH-related hospitalization in the combination therapy group, although a significant effect was not observed in a post-hoc analysis of all-cause hospitalization. METHODS: The effect of initial combination therapy with ambrisentan and tadalafil in AMBITION was further explored to study PAH-related hospitalization, which was not reported in the primary publication. RESULTS: Initial combination therapy was associated with a 63% reduction in risk of PAH-related hospitalization when compared with pooled monotherapy (hazard ratio [HR] 0.372, 95% confidence interval [CI] 0.217 to 0.639, p = 0.0002). For every 9 patients treated with combination therapy vs monotherapy, 1 PAH-related hospitalization could be prevented over a 1-year period. Serious adverse events leading to hospitalization, not necessarily PAH-related, occurred in 87 of 253 (34%) and 89 of 247 (36%) of patients on combination therapy and pooled monotherapy, respectively (post-hoc summary). CONCLUSIONS: Initial combination therapy with ambrisentan and tadalafil was found to reduce the risk of PAH-related hospitalization by 63% compared with pooled monotherapy.

Risk-stratified outcomes with initial combination therapy in pulmonary arterial hypertension: Application of the REVEAL risk score.

BACKGROUND: The multinational AMBITION study demonstrated a 50% risk reduction in time to first clinical failure event (TtCF, a composite of death, hospitalization for worsening pulmonary arterial hypertension [PAH], disease progression, or unsatisfactory long-term clinical response) in treatment-naive Functional Class II and III PAH patients initiated on combination therapy (ambrisentan and tadalafil) vs monotherapy. A post-hoc analysis of AMBITION data by risk stratification, as determined by baseline REVEAL risk score, was undertaken to better assess the impact of combination therapy. METHODS: Patients were randomized 2:1:1 to initial combination therapy with ambrisentan 10 mg plus tadalafil 40 mg vs either drug plus placebo, respectively. Baseline REVEAL risk scores in the 605 patients were grouped by low, intermediate, or high risk. Adjudicated outcomes (TtCF and post-hoc composite end-point of time to first PAH hospitalization or death) were assessed by risk group and treatment assignment. RESULTS: At baseline, risk groups were similarly represented across treatment assignments as low (16%), intermediate (46%), and high (38%) risk. Greater risk was associated with worse outcome. At each level of risk, patients on combination therapy had significantly fewer TtCF or PAH hospitalization/death events relative to those on monotherapy, and discontinuations due to adverse events were not higher on combination therapy. CONCLUSIONS: This post-hoc analysis comparing outcomes by REVEAL risk group has shown that, at all levels of risk, patients enrolled in AMBITION receiving initial combination therapy have superior outcomes and, even in those assessed as low risk, initial combination therapy was clinically beneficial.

Initial combination therapy with ambrisentan and tadalafil in connective tissue disease-associated pulmonary arterial hypertension (CTD-PAH): subgroup analysis from the AMBITION trial.

BACKGROUND: Patients with connective tissue disease-associated pulmonary arterial hypertension (CTD-PAH), in particular systemic sclerosis (SSc), had an attenuated response compared with idiopathic PAH in most trials. Thus, there is uncertainty regarding the benefit of PAH-targeted therapy in some forms of CTD-PAH. OBJECTIVE: To explore the safety and efficacy of initial combination therapy with ambrisentan and tadalafil versus ambrisentan or tadalafil monotherapy in patients with CTD-PAH and SSc-PAH enrolled in the AMBITION trial. METHODS: This was a post hoc analysis of patients with CTD-PAH and SSc-PAH from AMBITION, an event-driven, double-blind trial in patients with WHO functional class II/III PAH. Treatment-naive patients were randomised 2:1:1 to once-daily initial combination therapy with ambrisentan plus tadalafil or monotherapy with ambrisentan or tadalafil, respectively. The primary endpoint was time to the first clinical failure event (first occurrence of death, hospitalisation for worsening PAH, disease progression or unsatisfactory long-term clinical response). RESULTS: In the primary analysis set (N=500), 187 patients had CTD-PAH, of whom 118 had SSc-PAH. Initial combination therapy reduced the risk of clinical failure versus pooled monotherapy in each subgroup: CTD-PAH (HR 0.43 (95% CI 0.24 to 0.77)) and SSc-PAH (0.44 (0.22 to 0.89)). The most common AE was peripheral oedema, which was reported more frequently with initial combination therapy than monotherapy in the two PAH subgroups. The relative frequency of adverse events between those on combination therapy versus monotherapy was similar across subgroups. CONCLUSIONS: This post hoc subgroup analysis provides evidence that CTD-PAH and SSc-PAH patients benefit from initial ambrisentan and tadalafil combination therapy. TRIAL REGISTRATION NUMBER: NCT01178073, post results.

Ambrisentan use for pulmonary arterial hypertension in a post-authorization drug registry: The VOLibris Tracking Study.

BACKGROUND: The VOLibris Tracking (VOLT) Study was an open-label, prospective, observational, multicenter, post-marketing registry program designed to more fully characterize the safety profile of ambrisentan for the treatment of pulmonary arterial hypertension (PAH). The key outcome was the incidence of aminotransferase elevations >3× the upper limit of normal (ULN). METHODS: In total, 999 patients from 115 centers in 15 countries, who were prescribed ambrisentan for the treatment of PAH (Functional Class II and III) between 30 June 2008 and 13 May 2011, were enrolled. Of these, 238 had PAH associated with connective tissue disease (PAH-CTD) and 220 had no prior PAH-specific therapy. Routine clinical monitoring data were collected by physicians. RESULTS: The incidence of both alanine and aspartate aminotransferase events (>3× ULN) was 0.02 per patient-year (95% confidence interval 0.015 to 0.027). Similar results were reported for the PAH-CTD and PAH-specific-therapy-naive subgroups. Overall, 514 (52%) patients reported treatment-emergent adverse events of special interest, most commonly edema/fluid retention (249, or 25%) and anemia (143, or 14%). CONCLUSIONS: Data from the VOLT study indicate no new ambrisentan-related safety signals. Ambrisentan was not associated with increases in liver function test abnormalities above the assumed background incidence of 1.5% per year, and the observed safety profile of ambrisentan was consistent with previously published data.

Initial combination therapy with ambrisentan and tadalafil and mortality in patients with pulmonary arterial hypertension: a secondary analysis of the results from the randomised, controlled AMBITION study.

BACKGROUND: In treatment-naive patients with pulmonary arterial hypertension, initial combination therapy with ambrisentan and tadalafil reduces the risk of clinical failure events compared with monotherapy. We did this secondary analysis to further investigate the effect of combination therapy on survival. METHODS: We analysed survival data from the modified intention-to-treat population of the Ambrisentan and Tadalafil in Patients with Pulmonary Arterial Hypertension (AMBITION) trial. AMBITION was a multicentre, randomised, double-blind study, in which treatment-naive patients with pulmonary arterial hypertension were randomly assigned in a 2:1:1 ratio and received combination therapy with ambrisentan and tadalafil, ambrisentan and placebo, or tadalafil and placebo. We did a prespecified analysis of all mortality events from randomisation to the end of the study, including patients who discontinued their assigned treatment. In a post-hoc analysis, we analysed survival at 7 days after the termination of each individual patient's randomised treatment. We used Cox proportional hazard regression, Kaplan-Meier survival estimates, and the stratified log-rank test to compare the survival of patients receiving initial combination therapy or initial monotherapy. FINDINGS: The study population consisted of 605 patients with pulmonary arterial hypertension who were randomly assigned and received combination therapy (n=302) or monotherapy (n=303; 152 patients assigned to ambrisentan monotherapy and 151 patients to tadalafil monotherapy). At the end of the study, 29 (10%) of 302 patients in the combination therapy group had died compared with 41 (14%) of 303 patients in the monotherapy group (hazard ratio 0·67, 95% CI 0·42-1·08; stratified log-rank p=0·10). At 7 days after the end of randomised treatment, fewer patients had died in the combination therapy group (3 [1%] of 302 patients) compared with the monotherapy group (13 [4%] of 303 patients; hazard ratio 0·21, 95% CI 0·06-0·73). INTERPRETATION: These data indicate that initial combination therapy might be associated with a survival advantage compared with initial monotherapy in patients with newly diagnosed pulmonary arterial hypertension. This hypothesis needs to be addressed in future studies. FUNDING: Gilead, GlaxoSmithKline.

Initial Use of Ambrisentan plus Tadalafil in Pulmonary Arterial Hypertension.

BACKGROUND: Data on the effect of initial combination therapy with ambrisentan and tadalafil on long-term outcomes in patients with pulmonary arterial hypertension are scarce. METHODS: In this event-driven, double-blind study, we randomly assigned, in a 2:1:1 ratio, participants with World Health Organization functional class II or III symptoms of pulmonary arterial hypertension who had not previously received treatment to receive initial combination therapy with 10 mg of ambrisentan plus 40 mg of tadalafil (combination-therapy group), 10 mg of ambrisentan plus placebo (ambrisentan-monotherapy group), or 40 mg of tadalafil plus placebo (tadalafil-monotherapy group), all administered once daily. The primary end point in a time-to-event analysis was the first event of clinical failure, which was defined as the first occurrence of a composite of death, hospitalization for worsening pulmonary arterial hypertension, disease progression, or unsatisfactory long-term clinical response. RESULTS: The primary analysis included 500 participants; 253 were assigned to the combination-therapy group, 126 to the ambrisentan-monotherapy group, and 121 to the tadalafil-monotherapy group. A primary end-point event occurred in 18%, 34%, and 28% of the participants in these groups, respectively, and in 31% of the pooled-monotherapy group (the two monotherapy groups combined). The hazard ratio for the primary end point in the combination-therapy group versus the pooled-monotherapy group was 0.50 (95% confidence interval [CI], 0.35 to 0.72; P<0.001). At week 24, the combination-therapy group had greater reductions from baseline in N-terminal pro-brain natriuretic peptide levels than did the pooled-monotherapy group (mean change, -67.2% vs. -50.4%; P<0.001), as well as a higher percentage of patients with a satisfactory clinical response (39% vs. 29%; odds ratio, 1.56 [95% CI, 1.05 to 2.32]; P=0.03) and a greater improvement in the 6-minute walk distance (median change from baseline, 48.98 m vs. 23.80 m; P<0.001). The adverse events that occurred more frequently in the combination-therapy group than in either monotherapy group included peripheral edema, headache, nasal congestion, and anemia. CONCLUSIONS: Among participants with pulmonary arterial hypertension who had not received previous treatment, initial combination therapy with ambrisentan and tadalafil resulted in a significantly lower risk of clinical-failure events than the risk with ambrisentan or tadalafil monotherapy. (Funded by Gilead Sciences and GlaxoSmithKline; AMBITION ClinicalTrials.gov number, NCT01178073.).

The cost-effectiveness of bosentan in the United Kingdom for patients with pulmonary arterial hypertension of WHO functional class III.

OBJECTIVES: To assess whether bosentan or no active intervention, in addition to palliative care, is the more cost-effective first-line treatment option for patients with idiopathic pulmonary arterial hypertension (iPAH) or PAH associated with connective tissue disease (PAH-CTD) of WHO functional classification (FC) III in the United Kingdom. METHODS: A cost-utility model simulated the treatment of patients with PAH of FC III. Patients remained on the selected intervention until death or clinical deterioration to FC IV, which would trigger initiation of epoprostenol treatment. The initial first-line treatment choice was assumed to not affect survival, but to affect the time until clinical deterioration, with this assumption being relaxed in sensitivity analyses. The distribution of time to clinical deterioration was estimated from long-term clinical trial databases of bosentan and from published literature. Utility associated with FC was taken from published literature. Costs were sourced from published literature and from specialist PAH centers. The time horizon was that of patients' lifetimes, with costs and benefits discounted at 3.5% per annum. RESULTS: In the base case, bosentan dominated no active intervention because of the longer time to clinical deterioration and therefore the reduced time, per patient, spent in FC IV, which was associated with high costs of epoprostenol and reduced utility. In sensitivity analyses, bosentan was estimated to be more cost-effective than no active intervention, provided that any survival benefit was not greater than 2 years for patients with iPAH and 1 year for those with PAH-CTD. CONCLUSIONS: Bosentan is likely to be a more cost-effective first-line therapy for patients with PAH FC III in the UK than no active intervention.