Researchers found acetazolamide (sold as Diamox), which is already used to treat mountain sickness, improved overnight oxygen levels among people with the sleep disorder who spent time above 8,000 feet.

People who have sleep apnea stop breathing for short spurts when their airway collapses or gets blocked while they're asleep. The condition is most common among middle-aged, overweight adults and has been tied to a range of cardiovascular problems.

Because there is less oxygen in the air at high altitude, nighttime breathing symptoms may get worse far above sea level. However, there aren't any standard recommendations for mountain travelers with sleep apnea, according to Dr. Konrad Bloch, who worked on the new study.

"Physicians had no scientific evidence to counsel the patients," Bloch, from the University Hospital of Zurich, told Reuters Health.

To try to provide some guidance, his team sent 51 people with sleep apnea - all of whom lived at low altitude - to resorts in the Swiss Alps as high as 8,497 feet on two different trips.

Each time, the volunteers used a breathing device commonly prescribed to people with sleep apnea, called continuous positive airway pressure therapy, or CPAP, at night.

On one trip, participants also took three 250-milligram doses of acetazolamide each day. On the other, they were given drug-free placebo pills.

The dose of acetazolamide used here costs about $1.10 to $1.50 daily, the researchers noted. Along with being a diuretic, acetazolamide also triggers more frequent breathing.

Bloch and his colleagues found participants' average oxygen saturation overnight - a measure of sleep apnea severity - was better among the acetazolamide group, at 91 percent versus 89 percent in the placebo group at the highest altitude. (Normal oxygen saturation is between 97 and 99 percent.)

People taking acetazolamide also stopped breathing fewer times during the night than those taking the placebo pills, the research team reported Tuesday in the Journal of the American Medical Association.

With the type of CPAP used here, called autoCPAP, a computer controls air pressure flowing through the breathing mask. For standard CPAP - which is more common in the United States - pressure is calibrated in a sleep lab and doesn't change based on nightly variation.

Most of the study volunteers were moderately obese men. Any related conditions they had - such as diabetes or high blood pressure - were stable before the study.

WATCH FOR SIDE EFFECTS

Bloch said acetazolamide, which requires a prescription, "is not a harmless drug" because it alters water and salt content in the body. Some people in the study had side effects such as burning, numbness or tingling - and others complained about the drug's taste.

For patients with heart or kidney disease in addition to sleep apnea, acetazolamide could lead to more serious complications - by making them pee too much, said Dr. Seva Polotsky, a sleep apnea researcher from Johns Hopkins University School of Medicine in Baltimore.

"I think it's really beneficial. Having said that, you have to be careful with this drug," Polotsky, who wasn't involved in the new study, told Reuters Health.

"I would definitely check with a doctor and approach it very carefully."

The new research was partially funded by a grant from Philips Respironics, which markets sleep systems such as CPAP devices.

Bloch and Polotsky both recommended anyone traveling at altitude ascend slowly and take time to acclimatize along the way.

"This is a recommendation that is important for everyone, but especially those that have a breathing problem," Bloch said.

SOURCE: bit.ly/JjFzqx Journal of the American Medical Association, online December 11, 2012.

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