New drugs scale high-altitude pulmonary edema: novel therapies for prevention and treatment include inhaled [beta]-agonists, sildenafil, and dexamethasone.(Pulmonary Medicine)

SNOWMASS, COLO. -- Physicians have recently gained a brace of new pharmacologic options for preventing and treating high-altitude pulmonary edema, Peter Hackett, M.D., said at the annual meeting of the Wilderness Medical Society.

The novel therapies targeting this potentially lethal form of altitude sickness include sildenafil (Viagra for erectile dysfunction, Revatio for pulmonary arterial hypertension) and other phosphodiesterase-5 inhibitors; inhaled [beta]-agonists; and dexamethasone.

In addition, acetazolamide (Diamox)--used empirically for more than 3 decades to prevent high-altitude pulmonary edema (HAPE) in individuals with a history of HAPE--is, as a result of recent studies, "finally getting the respect it deserves" as an evidence-based prophylactic agent, said Dr. Hackett, director of emergency services at Telluride (Colo.) Medical Center and a faculty member at the University of Colorado Center for Altitude and Physiology, Boulder.

New therapies include:

* Sildenafil. The door was opened for this novel therapeutic application in mountaineering medicine by a landmark 2001 study in Kyrgyzstan showing that sildenafil blocked the typical hypoxia-induced increase in pulmonary artery pressure without affecting systemic arterial pressure, and with only a slight effect upon heart rate (Circulation 2001;104:424-8). Later studies demonstrated efficacy for the prevention of HAPE in high-risk individuals.

The mechanism of benefit is as follows: Sildenafil increases vascular smooth-muscle relaxation in the lung and penis by selectively blocking phosphodiesterase-5, found in those two organs. Phosphodiesterase-5 degrades cyclic guanosine monophosphate, a compound that causes vascular smooth-muscle relaxation.

"There's no question that Viagra is an excellent pulmonary vasodilator and is useful in HAPE. We're using it now for treatment as well as prevention, although the treatment studies really haven't been done yet," Dr. Hackett said.