Identification of predictors of response to initial oral combination therapy in WHO-functional class II or III PAH patients: a post-hoc analysis of the AMBITION study

Abstract

Abstract Background AMBITION Study (NCT01178073) provided the first long-term clinical evidence for initial combination therapy with ambrisentan and tadalafil (COMB) compared with monotherapy of either agent (MONO), and the results contributed to the ESC/ERS guidelines recommending initial combination therapy in PAH patients with low and intermediate risk. However, predictors of response to initial oral combination therapy to identify PAH patients who benefit most from it have not been assessed. Purpose To identify potential predictors of response to initial combination therapy with ambrisentan and tadalafil (COMB) in PAH patients with WHO-FC II or III in the AMBITION study. Methods We examined 302 COMB patients from the modified intention to treat (mITT) population enrolled in the AMBITION study (n=605). The mITT population includes PAH patients with risk factors related to heart failure with preserved ejection fraction (Ex-PAS) who were excluded from the primary analysis set (PAS). A responder (i.e. event-free subject) was defined as not having a clinical failure event. Univariate and multivariate analyses were performed to identify the factors associated with responders. Multivariate logistic regression analysis was used to determine independent risk for each factor that showed a significant difference between cohorts by interactive backward selection. Odds ratio (OR), 95% confidence intervals (CIs) and p-values are presented. Results Univariate analysis showed that responders tended to be lower age, female, typical PAH (i.e. PAS), absence of coronary artery disease, non-use of oxygen therapy, and have better baseline parameters (i.e., lower NT-proBNP, longer 6-minute walk distance, low Borg index, high SaO2, WHO-FC II). A multivariate logistic regression analysis showed that female gender (OR=2.669, 95% CI: 1.291–5.518, P=0.0081), use of aldosterone antagonist diuretics (OR=2.535, 95% CI: 1.027–6.257, P=0.0436), lower log NT-proBNP (OR=0.704, 95% CI: 0.524–0.944, P=0.0190), and longer 6-minute walk distance (OR=1.006, 95% CI: 1.002–1.010, P=0.0039) were independent predictors of response to initial combination therapy. Conclusion These findings suggest that initial combination therapy with ambrisentan and tadalafil is beneficial, especially in less severe typical PAH patients. It also demonstrates that there is a potential contributing factor (i.e. use of aldosterone antagonist diuretics) which is not listed in the risk assessment table of the ESC/ERS guidelines. Funding Acknowledgement Type of funding source: Private company. Main funding source(s): AMBITION study was funded by GlaxoSmithKline (GSK; study number 112565; trial registration number: NCT01178073) and Gilead Sciences, Inc. This analysis was funded by both companies.