Effect of transition from sitaxsentan to ambrisentan in pulmonary arterial hypertension

Zeenat Safdar
Division of Pulmonary-Critical Care Medicine, Baylor College of Medicine, Houston, Texas, USA

Introduction: Currently available endothelin receptor antagonists for treating pulmonary arterial hypertension block either the endothelin (ET) receptor A or both A and B receptors. Transition from one endothelin receptor antagonist to another may theoretically alter side-effects or efficacy. We report our experience of a transition from sitaxsentan to ambrisentan, both predominant ET_A receptor antagonists, in pulmonary arterial hypertension patients.
Methods: At Baylor Pulmonary Hypertension Center, 18 patients enrolled in the open-label extension phase of the original sitaxsentan studies (Sitaxsentan To Relieve ImpaireD Exercise) were transitioned to ambrisentan (from July 2007 to September 2007) at the time of study closure. Pre-transition (PreT), 1 month (1Mth) and 1 year (1Yr) post-transition assessments of 6-minute walk distance (6MWD), brain naturetic peptide (BNP) levels, WHO functional class (WHO FC), Borg dyspnea score (BDS), oxygen saturation, liver function, and peripheral edema were compared.
Results: 6MWD was 356 ± 126 m at PreT, 361 ± 125 m at 1Mth, and 394 ± 114 m at 1Yr (mean ± SD). There was no difference in the walk distance at 1Mth and 1Yr post transition compared with PreT (P = 0.92, 0.41 respectively). Oxygen saturation was no different at 1Mth and 1Yr to PreT level (P = 0.49 and P = 0.06 respectively). BNP was 178 ± 244 pg/mL at PreT, 129 ± 144 pg/mL at 1Mth and 157 ± 201 at 1Yr. Peripheral edema was present in 7/18 patients at PreT, in 8/16 patients at 1Mth, and in 6/13 patients at 1Yr post transition. Proportions of patients with edema over these 3 time points did not change significantly (P = 0.803). At 1Yr, 2 patients had died, 1 had undergone lung transplantation, 1 had relocated, and 1 patient was started on intravenous prostacyclin therapy. Over 3 points (baseline, 1 month, and 1 year), there was no significant change in function class (P = 0.672).
Conclusion: Our limited data suggest that ET_A receptor antagonists can be switched from one to another with sustained exercise capacity and maintained WHO FC with no increase in incidence of peripheral edema.

Keywords: right heart failure, 6-minute walk distance, endothelial receptor antagonist, echocardiogram