Pulmonary arterial hypertension: new insights into the optimal role of current and emerging prostacyclin therapies

Pulmonary arterial hypertension (PAH), which is a subset of pulmonary hypertension, is a group of diseases distinguished by vascular remodeling of the small pulmonary arteries with associated elevated pulmonary arterial pressure and right ventricular failure. This progressive and sometimes fatal disease occurs as an idiopathic disease or as a component of other disease states. Estimates of the incidence of PAH have varied from 5 to 52 cases/1 million population. Symptoms begin with shortness of breath with exertion and progress to dyspnea with normal activities and, finally, dyspnea at rest. Untreated patients with PAH have a 1-, 3-, and 5-year survival rate of 68%, 48%, and 34%, respectively. Treated, the survival rates improve to 91% to 97% after 1 year and 84% to 91% after 2 years. The current definition of PAH consists of 3 specific hemodynamic assessments confirmed by right heart catheterization findings. One of several important pathophysiologic mechanisms involved in PAH is pulmonary vascular remodeling, which is caused by endothelial and smooth muscle cell hyperproliferation. This is coincident with overexpression of the vasoconstrictor endothelin-1 and a reduction in the vasodilators nitric oxide and prostacyclin, which further impedes proper vasomotor tone, among other effects. Prostacyclin therapies augment the decreased prostacyclin levels in patients with PAH. The currently approved prostacyclins for the treatment of PAH include epoprostenol, iloprost, and treprostinil. Among the 3 medications, the delivery options include intravenous infusion, subcutaneous infusion, and inhaled formulations. Epoprostenol has been shown to have a positive effect on survival in patients with PAH. All prostacyclins have demonstrated improvements in functional class, exercise tolerance, and hemodynamics in patients with PAH. Intravenously and subcutaneously administered formulations of prostacyclins require continuous infusion pump administration, which presents clinical challenges for both the patient and the care provider. Dosing must be individualized and also presents a clinical challenge. Inhaled formulations seem efficacious in moderately symptomatic patients with PAH and might be appropriate when combined with an oral medication. Combination therapies are commonly used in clinical practice, with the decision to do so based on randomized controlled trial data and case study evidence. The present report provides an overview of PAH, the scientific rationale for treatment with prostacyclin therapy, and the benefits and risks of prostacyclin therapy, both as monotherapy and combined with other medications approved for the treatment of PAH.

Combination Pharmacotherapy in the Treatment of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a disorder of the small pulmonary arteries characterized by progressive fibrotic and proliferative changes that result in an increased pulmonary vascular resistance. It is a progressive and debilitating disease that leads to right ventricular dysfunction, impairment in activity tolerance and eventually right-sided heart failure, and premature death. The treatment goals for PAH include improvement in symptoms, improvement in functional class and exercise class, decreased morbidity, and preventing mortality. Combination therapy in the treatment of PAH is an emerging therapeutic option. Combining therapies with differing mechanisms of action will maximize therapeutic benefits such as symptom control and increased rate of survival. The updated 2007 American College of Chest Physicians evidence-based clinical practice guidelines recommend combination therapy in functional classes III and IV if there is no improvement with current therapy or if there is deterioration in class. PAH monotherapy has been shown to improve symptoms, but the patients’ hemodynamic parameters may not be normalized, leading to further pulmonary vascular remodeling. Combination therapy offers an additional option for those patients who are unable to stabilize on monotherapy.

Targeted approaches to the treatment of pulmonary hypertension

Pulmonary arterial hypertension is a progressive and incurable disease. Over the past two decades, significant advances have been made in understanding and thus managing this disease. Multiple therapeutic options are currently available and optimizing the treatment of pulmonary arterial hypertension has become complex. Patients who meet the American College of Chest Physicians criteria for vasoresponsiveness can be safely and effectively treated with high-dose calcium channel blockers but require close follow up to assure durability of response. Patients with World Health Organization (WHO) functional class IV status and those with determinants of high risk for progression and death should be treated with an infused prostanoid agent without delay. These patients should also be referred early after stabilization for transplant evaluation. Patients with WHO functional class II status benefit from early initiation of oral therapies. Those with WHO functional class III status and lower determinants of risk for progression may receive treatment with one or more oral or inhaled agents, though many experts would advise early use of infused prostanoids for these patients as well.

Combination therapy: the next opportunity and challenge of medicine

From an historical point of view, combination therapy was the basis for the care of important diseases like infection diseases or cancer. Today the "cocktail drug" of the Highly Active Anti Retroviral Therapy (HAART) has reduced the death for HIV infection changing the outcome of such disease. Moreover, the combination of different strategies changed the course of transplants (both in haematology and surgical transplant). Different diseases with high social impact including cardiovascular, metabolic (obesity, hypercholesterolaemia and diabetes) and autoimmune diseases, have better results with combinations of different drug classes of drugs. After recent successes in the immunotherapy field (Sepuleucel-T, ipilimumab) and the new promising small molecule therapies, cancer should be the next challenge for combination strategies.