The Efficacy and Safety of Vardenafil in the Treatment of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH), defined as a mean pulmonary artery pressure ≥25 mmHg with a pulmonary capillary wedge pressure ≤15 mmHg measured by cardiac catheterization, is a disorder that may occur either in the setting of a variety of underlying medical conditions or as a disease that uniquely affects the pulmonary circulation. Irrespective of its etiologies, PAH is a serious and often progressive disorder that results in right ventricular dysfunction and impairment in activity tolerance, and may lead to right-heart failure and death. The pathogenesis of PAH is complex and incompletely understood, but includes both genetic and environmental factors that alter vascular structure and function. In recent years, several new drugs have been developed for the treatment of pulmonary arterial hypertension (PAH), including continuous intravenous epoprostenol, inhaled iloprost, subcutaneous trepostinil, oral bosentan, and oral beraprost. In addition, there is increasing evidence for the therapeutic effectiveness of the phosphodiesterase-5 (PDE-5) inhibitor sildenafil in PAH. Phosphodiesterases are a superfamily of enzymes that inactivate cyclic adenosine monophosphate and cyclic guanosine monophosphate, the second messengers of prostacyclin and nitric oxide (NO) .The phosphodiesterases have different tissue distributions and substrate affinities. Interestingly, PDE-5 is abundantly expressed in lung tissue, thus offering as target molecule for PAH treatment concepts. The three commercially available PDE-5 inhibitors (sildenafil, vardenafil, and tadalafil) are currently approved for the treatment of erectile dysfunction . These inhibitors are now receiving attention for their activity in the pulmonary vasculature. Sildenafil has been proved to improve the exercise capacity and pulmonary hemodynamics of PAH patients, however, there are few reports regarding the use of vardenafil or tadalafil on the pulmonary vasculature. Although sildenafil, vardenafil, and tadalafil act on the same enzyme, these drugs exhibit different pharmacokinetics and selectivity, and therefore may not be equally efficacious in the pulmonary vascular bed. As vardenafil has a more than 20-fold greater potency than sildenafil for inhibiting purified PDE-5, we assume that it will show more favorable clinical and side-effect profiles in treating PAH. This is a prospective, randomized, placebo-controlled, pilot study to evaluate the efficacy and safety of vardenafil in the treatment of pulmonary arterial hypertension.