[64-66]Acetazolamide and low-dose sustained-release theophylline both appear to act by increasing central stimulation of respiratory drive,[67, 68] and both improve sleep-disordered breathing. There are insufficient data to advocate prevention with hypnotic agents alone or in combination with other drugs.[56] Dexamethasone is a powerful drug with the potential to prevent AMS, HACE, and HAPE.[69-71] However, in contrast to acetazolamide, dexamethasone does not assist in the process of acclimatization.[11] The calcium-channel blocker nifedipine and the phosphodiesterase-5 inhibitor tadalafil reduce pulmonary hypertension, and have been shown in demonstration

PD0325901 molecular weight studies to prevent HAPE in HAPE-susceptible RGFP966 subjects.[23, 71] Beta2-agonists such as salmeterol facilitate alveolar fluid clearance, and have also been shown to prevent HAPE in susceptible individuals.[72] However, they are not as effective as nifedipine and tadalafil for this purpose. Once promising, ginkgo biloba has no specific or additional preventive effect on AMS.[83] Beneficial preventive effects have been reported by two recent studies on the use of sumatriptan or gabapentin for AMS prophylaxis.[84,

85] However, further studies are required before a firm conclusion can be reached.[86] The low oxygen environment at high altitude is the primary cause of all hypoxia-related high-altitude illness.[87] Thus, descent from high altitude represents the therapy of choice, with medications including oxygen

as adjunctive measures. Self-medication for moderate to severe AMS, HACE, or HAPE is untested, but commonly used. If the traveler is part of a group trek or expedition, adequate treatment is ideally provided by an experienced physician, or realistically by a trained guide or someone with adequate medical training. In mild AMS (ie, a Lake Louise score of 4–9), the affected person can stay at that altitude, relax, take antiemetics, maintain fluid intake, and take pain relievers until symptoms subside. If symptoms persist or are even intensified, descent is recommended. For severe AMS, HAPE, and HACE, oxygen (4–6 L/min) all should be given while planning descent and evacuation if available. Other nonpharmacologic measures to increase oxygenation include pursed lip breathing, application of positive airway pressure by a helmet or facemask, and use of a portable hyperbaric chamber.[11, 88, 89] Simultaneously with these measures, appropriate drug therapy should be started. There are only a few drugs that have proven effectiveness for the treatment of high-altitude illnesses. Acetazolamide (a carbonic anhydrase inhibitor) can be used to treat mild AMS, but should be avoided in pregnancy.[73] Again, NSAIDs (eg, ibuprofen, naproxen, and aspirin) and acetaminophen are effective for treating headache at high altitude.[74, 75] Dexamethasone (a corticosteroid) is an excellent drug to treat AMS and HACE.