Trip Answers

Question answered:06/09/06 Warning! this question is over two years old.

The NLH Q & A Service cannot advise on the prescribing of medication for individual patients, we simply present findings and recommendations from evidence-based sources to aid clinicians decision making. Although we located information supporting the effectiveness of acetazolamide in preventing altitude sickness, none of it specifically considered its use in older patients.

We searched the BNF for prescribing indications and instructions for acetazolamide, as well as the Medicines.org.uk websites for an SPC but found none.

Concerning the efficacy of acetazolamide to prevent altitude sickness, the NLH Q & A Service produced an answer on this topic in which it concludes that acetazolamide is effective in preventing altitude sickness in altitudes above 3800m. This answer, posted in August 2006, which also discusses adverse effects of Diamox may be viewed in full at: http://www.clinicalanswers.nhs.uk/index.cfm?question=3601 [1]

An e-Medicine article, on altitude sickness notes:

“The high altitude environment generally refers to elevations over 1500 m (4900 ft). Moderate altitude, 2000-3500 m (6600-11,500 ft) includes the elevation of many ski resorts. Although arterial oxygen saturation is well maintained at these altitudes, low PO2 results in mild tissue hypoxia, and altitude illness is common. Very high altitude refers to elevations of 3500-5500 m (18,000 ft). Arterial oxygen saturation is not maintained in this range, and extreme hypoxemia can occur during sleep, with exercise or illness. HACE [high altitude cerebral edema] and HAPE [high altitude pulmonary edema] are most common at these altitudes. Extreme altitude is over 5500 m; above this altitude successful long-term acclimatization is not possible and in fact deterioration ensues. Individuals must progressively acclimatize to intermediate altitudes to reach extreme altitude.”

The section on medication gives the following prescribing instructions:

“Acetazolamide (Diamox) -- Carbonic anhydrase inhibitor for accelerating acclimatization to altitude in AMS. Helps prevent AMS in forced rapid ascent or in patients with history of repeated AMS. Improves symptomatic periodic breathing and hypoxia experienced at high altitudes. Not indicated for general prophylaxis of AMS. Treatment of AMS may be discontinued when patient is asymptomatic.
Adult dose: Immediate release dosage form: 250 mg PO q12h
Prophylaxis of AMS (if indicated): 125 mg PO q12h beginning 24 h before ascent and continuing during ascent to at least 48 h after arrival at highest altitude (or descent)
For periodic breathing: 125 mg PO at bedtime until below the altitude at which periodic breathing began disturbing sleep.
Contraindications: Documented hypersensitivity; hepatic disease; severe renal disease; adrenocortical insufficiency; severe pulmonary obstruction
Interactions: Can decrease therapeutic levels of lithium; alters excretion of certain drugs (eg, amphetamines, quinidine, phenobarbital, salicylates) by causing alkalinization of the urine.” [2]

NHS Direct has produced a patient information leaflet on altitude sickness which states:

“Altitude sickness (also known as acute mountain sickness) can occur in its mildest form at around 2500m (8000ft) above sea level (common ski resort height), but is more likely to occur, and to be more severe, at higher altitudes of 3500m (11000ft)and above…”
“Acetazolamide is a prescription only drug, so you need to see your doctor to obtain it. The recommended dose is 250mg (one tablet) twice a day when required. You should start taking it 24-48 hours before you go to altitude and continue with the treatment while ascending, until you are fully acclimatised to your final altitude. You should be aware, however, that there are some minor side effects associated with acetazolamide such as, paraesthesia (numbness, tingling or pricking sensation of the skin), polyuria (making a lot of urine) and blurred vision.” [3]

References
1. NLH Q & A Service. How useful is Diamox for treating and preventing altitude sickness? August 2006. (http://www.clinicalanswers.nhs.uk/index.cfm?question=3601)
2. Dietz M. Altitude illness – cerebral syndromes. E-Medicine. July 2006. (http://www.emedicine.com/emerg/topic22.htm).
3. NHS Direct. Altitude sickness. July 2006. (http://www.nhsdirect.nhs.uk/articles/article.aspx?articleId=13&sectionId=17267; http://www.nhsdirect.nhs.uk/articles/article.aspx?articleId=13&sectionId=17272).

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