The AMBITION study (NCT01178073) provided the first long-term clinical evidence for initial combination therapy with ambrisentan and tadalafil in patients with pulmonary arterial hypertension (PAH). Nevertheless, predictors of treatment response were not assessed. To identify predictors for response to initial combination therapy, we examined pdata from 302 patients with PAH (World Health Organization Functional Class II or III) who received initial combination therapy from the modified intention-to-treat population of the AMBITION study (n = 605). A responder was defined as not having undergone a clinical failure event. Univariate and multivariate analyses were performed. Multivariate logistic regression with interactive backward selection was used to assess the independent association of potential predictors with response. Treatment responders were younger, more often female, and less likely to have comorbidities or a requirement for oxygen therapy, compared with nonresponders. At multivariate analysis, female sex (odds ratio [OR] 2.67; 95% confidence interval [CI] 1.29, 5.52; P = 0.0081), longer 6-minute walk distance (OR 1.01; 95% CI 1.00, 1.01; P = 0.0039), lower baseline log N-terminal-prohormone of brain natriuretic peptide (OR 0.70; 95% CI 0.52, 0.94; P = 0.0190), and aldosterone antagonist use (OR 2.54; 95% CI 1.03, 6.26; P = 0.0436) independently predicted response to initial combination therapy. Besides demographic factors, the absence of comorbidities and less severe disease state, and the use of aldosterone antagonist therapy identified patients with PAH most likely to respond to initial combination therapy with ambrisentan and tadalafil. Further study to evaluate the role of aldosterone antagonist therapy in PAH is warranted.
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