When High Altitude Knocks You Down

Acetazolamide for altitude illness has limited effectiveness depending on situation

(RxWiki News) If you're headed for some mountain vacations this summer, you may be wondering whether you should get a prescription for altitude illness "just in case."

The drug acetazolamide is sometimes prescribed to help with altitude illness for mountain climbers, skiers, hikers and anyone else spending time at very high elevations, generally anything over about 8,000 feet (2400 meters).

But a recent review of the research literature on the effectiveness of acetazolamide to treat and prevent acute mountain sickness has found conflicting and inconclusive results.

"Visit a travel clinic before any extreme travel."

Bengt Kayser, MD, PhD, of the Institute of Movement Sciences and Sports Medicine at the University of Geneva in Switzerland, led the study, which analyzed 24 studies on the effectiveness, side effects and risks of taking acetazolamide.

The studies included data from a combined 1,011 people who took acetazolamide in 250, 500 or 750 mg daily and 854 people who took a placebo. In short, the researchers found that the effectiveness of the drug depends on the person, how high they're going and how fast they're ascending.

Acute mountain sickness occurs in high elevation environments because of the lower air pressure and lower levels of oxygen. It's more likely to strike the faster someone ascends.

Those at a higher risk for developing acute mountain sickness are those who live at or near sea level and those who have had it previously. A person is less likely to get it if they acclimatize gradually to higher elevations, though anyone over 13,000 feet is at a higher risk for developing it.

The most common symptoms include a headache as well as a lack of appetite, nausea and vomiting, fatigue, dizziness and difficulty in sleeping.

The condition can be mild, but it can also be fatal, and the only safe treatment is to descend to a lower elevation. Additional treatment can include breathing pure oxygen and taking acetazolamide.

The general finding was that acetazolamide's effectiveness is fairly limited for people who are slowly ascending high altitudes, which is the more likely and more recommended way to reach high altitudes so that a person's body gradually gets used to the effects of higher elevation. As they acclimatize, their bodies produce more red blood cells to compensate for the reduced concentration of oxygen in the air they're breathing in.

The study found that among slow ascenders (14 meters per hour), about 34 percent of people develop acute mountain sickness, and five to seven people would need to take acetazolamide for one of them to benefit from the medication.

However, acetazolamide is more effective for people who will be rapidly ascending from a lower elevation to a higher one, such as traveling from a beach to a high elevation in the mountains.

In this case, when people are ascending at a rate of about 130 to 500 meters per hour, about 60 percent of them will develop acute mountain sickness, and only three people need to take the drug for one of them to benefit.

The recommended speed of ascent to reduce the risk of altitude illness is to climb no more than 2,000 feet per day above elevations of 8,000 feet. Other behaviors that reduce a person's risk are drinking plenty of fluids and eating regular meals that are high in carbohydrates.

The most common side effect effect of acetazolamide, which occurs with any dosage, is numbing or tingling sensations in the hands or feet, similar to the feeling when a limb "falls asleep."

Two other common side effects - a need to urinate often and a strange taste in the mouth - tend to occur more with dosages of 500 mg and 750 mg a day.

The researchers concluded that the use of acetazolamide depends on the individual's risk of developing acute mountain sickness and whether they are willing to deal with the possible side effects.

Regardless of whether a person is taking acetazolamide or not, if they experience any of the symptoms of acute mountain sickness, they should begin descending immediately.

If the symptoms continue or become worse, they should seek medical attention immediately to prevent the possibility of brain swelling or gathering liquid in their lungs, both of which can lead to death.

The study was published June 22 in the journal High Altitude Medicine and Biology and is freely available to the public. The research was funded by the University of Geneva, and the authors declared no conflicts of interest.

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Review Date: 
July 16, 2012