In the beginning, it gave hope to older men trying to give their sexual performance a lift.
Now sildenafil, better known by its trade name, Viagra, is gaining popularity for a different use among skiers and mountain climbers. Their concern: avoiding high-altitude pulmonary edema, a potentially deadly condition in which excess fluid collects in the lungs.
Research has been accumulating about sildenafil's value in nonsex-related uses. The drug has been shown to help some people with high blood pressure in arteries supplying the lungs, a condition known as pulmonary hypertension.
Studies on its use for pulmonary edema include one published in the Annals of Internal Medicine in August. German researchers found that the drug not only prevented this type of edema but also increased the ability to exercise at altitude.
"It's still preliminary and needs to be better studied," says Dr. Peter Hackett, a founding member of the Wilderness Medical Society, a Colorado-based association focused on health in remote environments. "People should not just be running out and buying this stuff because they are going" to high altitudes.
Hackett, director of emergency services at the Telluride Medical Center in Colorado, has studied the drug. He says people who have a history of pulmonary edema and are bound for high-altitude hiking or skiing might consider taking sildenafil as a preventive but only with their doctor's OK. He has used sildenafil to treat pulmonary edema with good results, he says, though he would not routinely recommend the drug.
Sildenafil has not been shown to relieve the more common type of altitude sickness known as acute mountain sickness, or AMS, says Dr. Robert "Brownie" Schoene, past president of the Wilderness Medical Society and professor at UC San Diego School of Medicine. Symptoms include headache, nausea, loss of appetite and difficulty sleeping.
"AMS can occur at altitudes of 6,000 to 8,000 feet," Schoene says. Descent often helps; if symptoms persist or are severe, medical help is recommended.
By contrast the symptoms of high-altitude pulmonary edema, or HAPE, include shortness of breath, fatigue and cough, sometimes with frothy, pink sputum. Schoene says the condition has been recorded at 8,000 feet but is much more common at 9,000 to 12,000 feet, and the onset is usually two to four days after arrival.
"In our emergency room, we probably see a dozen cases of HAPE a year," says Dr. Chris Hummel, director of the emergency department at Mammoth Hospital in Mammoth Lakes.
Confirmed diagnoses of acute mountain sickness occur at about the same rate, Hummel says, "but we suspect the number is actually … higher. Many with acute mountain sickness don't come to the ER."
Treatment typically involves supplemental oxygen and the drug nifedipine (Adalat, Procardia), which lowers pulmonary artery pressure.
"It's the same concept as sildenafil, but sildenafil is more potent than nifedipine," Schoene says. In the lungs, sildenafil keeps the blood vessels dilated, he says. Pressure doesn't build, and the vessels don't leak fluid into the lungs' tiny air sacs.
For mountain climbers, a typical dose of sildenafil is 50 milligrams every eight hours, Hackett says. To treat erectile dysfunction, the usual dose is 50 milligrams before sex, he says.
Unwanted sexual arousal usually is not a problem, Hackett says. "There has to be sexual stimulation, which is usually not available on a mountain-climbing expedition. You are just struggling to survive."