Inhaled Therapies for Pulmonary Hypertension

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Abstract
The inhaled route has a number of attractive features for treatment of pulmonary hypertension, including delivery of drug directly to the target organ, thus enhancing pulmonary specificity and reducing systemic adverse effects. It can also improve ventilation/perfusion matching by dilating vessels supplying ventilated regions, thus improving gas exchange. Furthermore, it can achieve higher local drug concentrations at a lower overall dose, potentially reducing drug cost. Accordingly, a number of inhaled agents have been developed to treat pulmonary hypertension. Most in current use are prostacyclins, including epoprostenol, which has been cleared for intravenous applications but is used off-label in acute care settings as a continuously nebulized medication. Aerosolized iloprost and treprostinil are both prostacyclins that have been cleared by the FDA to treat pulmonary arterial hypertension (PAH). Both require frequent administration (6 and 4 times daily, respectively), and both have a tendency to cause airway symptoms, including cough and wheeze, which can lead to intolerance. These agents cannot be used to substitute for the infused routes of prostacyclin because they do not permit delivery of medication at high doses. Inhaled nitric oxide (INO) is cleared for the treatment of primary pulmonary hypertension in newborns. It is also used off-label to test acute vasoreactivity in PAH during right-heart catheterization and to treat acute right-heart failure in hospitalized patients. In addition, some studies on long-term application of INO either have been recently completed with results pending or are under consideration. In the future, because of its inherent advantages in targeting the lung, the inhaled route is likely to be tested using a variety of small molecules that show promise as PAH therapies.

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