Drug treatment of pulmonary arterial hypertension: current and future agents

During the last decade we have witnessed substantial improvements in the therapeutic options for pulmonary arterial hypertension (PAH), including true innovations targeting some of the mechanisms involved in the pathogenesis of this devastating disease. Intravenous epoprostenol was the first drug to improve symptoms and survival of patients with PAH. Novel prostanoids, including subcutaneous treprostinil and inhaled iloprost, also have beneficial effects in many patients, although their long-term efficacy is less well known. Among the newer treatments for PAH, endothelin receptor antagonists and phosphodiesterase type 5 (PDE5) inhibitors have reshaped clinical practice. The endothelin receptor antagonist bosentan has been approved in many parts of the world and most current guidelines recommend this drug as first-line treatment for patients with PAH in functional class III. Novel endothelin receptor antagonists such as sitaxsentan sodium and ambrisentan are currently being investigated. The PDE5 sildenafil is also being intensively studied in patients with pulmonary hypertension, and most of the available data look promising, although approval for PAH is still pending. Other PDE5 inhibitors have not yet undergone extensive study in PAH. The increasing insight into the pathogenesis of PAH opens several new therapeutic opportunities, which include vasoactive intestinal peptide, selective serotonin reuptake inhibitors, adrenomedullin and HMG-CoA reductase inhibitors (statins). However, PAH is a complex disorder and targeting a single pathway can not be expected to be uniformly successful. Thus, combining substances with different modes of action is expected to improve symptoms, haemodynamics and survival in PAH patients, although combination therapy has yet to undergo the scrutiny of large randomised clinical trials.