Acetazolamide

What is Acetazolamide?

Acetazolamide is a type of diuretic (‘water pill’) known as a carbonic anhydrase inhibitor. It is used to treat certain types of seizures, glaucoma and limit the build-up of body fluids caused by congestive heart failure. It is also commonly used to manage altitude sickness by decreasing headaches, tiredness, nausea, dizziness and shortness of breath, which occur when climbing to high altitudes - usually above 2,500 metres.

How does Acetazolamide work?

Acetazolamide is not an immediate cure for altitude sickness - it speeds up acclimatisation and reduces symptoms. It causes the kidneys to excrete bicarbonate, causing the blood to become more acidic. This rise in blood acidity tricks the body into thinking it has an excess of carbon dioxide, which it seeks to excrete through deeper and more regular breathing. In doing so, the body increases the amount of oxygen in the blood, which helps reduce the symptoms of altitude sickness.

Who should take Acetazolamide?

Acetazolamide can help you adjust to high altitudes and prevent altitude sickness symptoms. You can take Acetazolamide if you are planning to walk or climb to high altitudes. You should start taking Acetazolamide one or two days before you begin to ascend to high altitudes and follow standard precautions. Acetazolamide can be used to reduce the symptoms of altitude sickness, but will not completely cure them. If you are already taking Acetazolamide and begin to experience altitude sickness, you must stop your ascent or descend by at least 500m.

How long does it take for Acetazolamide to work?

You can take Acetazolamide to prevent altitude sickness rather than treat it. Start taking Acetazolamide one or two days before you begin your ascent to altitudes of 2,500m and above to allow your body to get used to Acetazolamide and adjust accordingly. You should continue to take Acetazolamide as you ascend and 24 hours after remaining at a constant altitude. 

It is unknown if Acetazolamide is effective in treating the symptoms of altitude sickness after they occur. Using Acetazolamide as treatment can take up to 48 hours to take effect, by which time your body may well have adjusted on its own.

Is Acetazolamide for altitude sickness off-label use?

Acetazolamide was initially licensed for use in the treatment of glaucoma and epilepsy. However, it has since been used as an effective method to prevent altitude sickness. Although the original license has not been extended to cover altitude sickness, it does not mean that it is unsafe or ineffective. It is an expensive process to get a license extended, so manufacturers often avoid doing this. Doctors can prescribe medications off-label when there is evidence to suggest that it is the most appropriate treatment available. The NHS has produced a useful document on this subject which you can access here for more information.

How to acclimatise to high altitude?

When travelling to altitudes above 2,500 metres, the best way to acclimate yourself and avoid altitude sickness is to make your ascent slowly. It usually takes your body a few days to get used to a change in altitude, so you should take two to three days to rest and adapt before ascending further than 2,500m. Take the following precautions as you climb to higher altitudes:

• Avoid climbing more than 300m to 500m per day
• Spend a day resting after every 600m to 900m, or rest every three to four days
• Drink plenty of water
• Avoid strenuous exercise, particularly in the first 24 hours
• Try and eat a light but high-calorie diet
• Avoid alcohol or smoking

How to relieve symptoms of altitude sickness?

Altitude sickness symptoms can include headaches, nausea and vomiting, dizziness, tiredness, loss of appetite, and shortness of breath. These symptoms commonly worsen during night-time. If you think you have symptoms of altitude sickness, the following advice may help:

• Stop and rest
• Do not ascend further for at least 24 to 48 hours
• Make sure you are drinking plenty of water
• Avoid exercise
• Avoid smoking or drinking alcohol
• Take painkillers, such as paracetamol, to relieve your headache
• Take anti-sickness medication if you feel nauseous 

Can Acetazolamide be crushed?

Acetazolamide tablets for altitude sickness should not be crushed or chewed. Tablets are designed to work over several hours and should be swallowed whole with a drink of water.

How to take Acetazolamide?

Take Acetazolamide as instructed by your doctor. Long-acting tablets (250 mg) should be taken twice daily, beginning at least 24 hours before ascending to high altitudes (2,500m and above). These tablets are designed for extended-release, so you mustn’t chew or crush them, but swallow them whole with a drink of water.

Acetazolamide dosage

One tablet contains 250 mg of Acetazolamide. For rapid ascension to high altitude, take one tablet twice daily, beginning one or two days before starting your ascent. If taking this medication to relieve symptoms of altitude sickness, take half a tablet twice daily.

Acetazolamide side effects

Some people may experience mild side effects when taking Acetazolamide, including:

• Headaches and dizziness
• Nausea, vomiting, loss of appetite or thirst
• Diarrhoea
• Tiredness or irritability
• The need to pass urine more than usual
• Feeling over-excited and appearing flushed
• Tingling or numbness in fingers or toes, or loss of total control of arms or legs

Less common side effects include:

• Drowsiness or confusion
• Depression
• Loss of sexual appetite
• Ringing in the ears or difficulty hearing
• Temporary short-sightedness, which subsides when the dosage is reduced

Like all medicine, Acetazolamide can cause severe allergic reactions, although this is very rare. You should seek emergency medical help immediately if you experience any sudden wheezing, difficulty breathing, swelling of the eyelids, face or lips, rash or itching. 

In rare cases, Acetazolamide can affect blood cells, increasing your chance of catching infections and affecting your blood’s ability to clot properly. Contact your doctor immediately if you have a sore throat or fever, or notice bruises or tiny red spots on your skin whilst taking this medication. If your muscles feel weak, or you have seizures, seek urgent medical attention.

Acetazolamide can also very rarely affect the liver and kidneys. You should contact a doctor if you experience pain in your lower back, pain or difficulty passing urine, inability to pass urine, blood in your urine, pale stools, or yellowing of your skin or the whites of your eyes.

Contraindications

You should not take Acetazolamide tablets if:

• You are pregnant, think you might be pregnant or are planning on becoming pregnant.
• You are allergic to sulfonamides, sulfonamide derivatives, or any of the listed ingredients in the Patient Information Leaflet
• You have severe liver problems
• You have kidney problems
• You have chronic non-congestive angle-closure glaucoma
• You have reduced function of the adrenal glands (Addison’s disease)
• You have low blood levels of sodium or potassium
• You have high blood levels of chlorine

Drug interactions

You should let your doctor know if you are taking other medicines or plan to take other medicines whilst taking Acetazolamide. The effects of the following medicines, in particular, may be altered by taking Acetazolamide:

• Medicines for the heart, such as cardiac glycosides
• Medicines to reduce blood pressure
• Blood-thinning medications
• Medicines to reduce blood sugar levels
• Epilepsy medication
• Medicines that interfere with folic acid
• Steroids
• Aspirin
• Other types of carbonic anhydrase inhibitors
• Amphetamines, quinine, methenamine or lithium
• Sodium bicarbonate therapy
• Ciclosporin

Acetazolamide and alcohol

Avoid drinking alcohol when taking Acetazolamide as the combination increases the risk of experiencing drowsiness. If taking Acetazolamide for altitude sickness, alcohol should be avoided at all costs, as the dehydrating effect of alcohol can make the symptoms of altitude sickness worse.

Acetazolamide vs Diamox

Diamox is a brand name for Acetazolamide, which is the generic name for the drug. As of April 2015, it is no longer possible to buy Diamox in the UK. The treatment is now sold generically as ‘Acetazolamide’ and contains the same dosage and ingredients as the original Diamox.

Alternatives to Acetazolamide

There are measures for managing altitude sickness, which you should follow regardless of whether you have chosen to take Acetazolamide. Acetazolamide is designed to reduce the severity of your symptoms rather than prevent or cure them altogether. Taking the following precautions can be equally as effective in preventing altitude sickness:

• Avoid climbing more than 300m to 500m per day
• Spend a day resting after every 600m to 900m, or rest every three to four days
• Drink plenty of water
• Avoid strenuous exercise, particularly in the first 24 hours
• Try and eat a light but high-calorie diet
• Avoid alcohol or smoking

What should you do if you begin to experience altitude sickness?

If you begin to experience symptoms of altitude sickness, see the following measures:

• Stopping your ascent for at least 24 to 48 hours
• Drink plenty of water
• Avoid strenuous activity or exercise, and rest completely for 24 hours
• Avoid smoking and drinking alcohol
• Take painkillers, such as Paracetamol, to relieve your headache
• Take anti-sickness medication if you feel nauseous

Can you buy Acetazolamide over the counter?

You cannot buy Acetazolamide over the counter at a pharmacy. It must be prescribed by a travel doctor, GP or online pharmacy. Although it is not currently licensed in the UK as a treatment for altitude sickness, it can be legally prescribed for this purpose.

How does Acetazolamide affect blood pressure?

There is some evidence to suggest that Acetazolamide can help lower blood pressure. Through encouraging the body to increase its oxygen intake, Acetazolamide helps reduce the rise in blood pressure associated with an increase in altitude.

Does Acetazolamide help Ménière’s disease?

Ménière’s disease is characterised by vertigo, a ringing sound in the inner ear, a feeling of pressure deep inside the ear and a sudden loss of hearing. While the exact cause of Ménière’s disease is unknown, it is associated with an increase in pressure inside the inner ear. 

The most common treatments recommended by GPs are Prochlorperazine, which helps relieve severe nausea and vomiting, and antihistamines, which help relieve mild nausea, vomiting and vertigo. However, diuretics such as Acetazolamide can treat Ménière’s disease, relieving the inner ear fluid build-up and reducing vertigo and hearing loss.

Can Acetazolamide be used for migraines?

Those who suffer from migraines triggered by travelling to high altitudes may find that taking Acetazolamide two to three days before their trip prevents migraines from occurring. However, there is little evidence suggesting that taking Acetazolamide is beneficial to those who suffer from migraines unrelated to altitude changes. 

Active ingredients

The active ingredient is acetazolamide. Each tablet contains a 250mg dose of acetazolamide.

Inactive ingredients

The inactive ingredients in Acetazolamide 250mg tablets are dicalcium phosphate, corn starch, magnesium stearate, sodium starch glycolate and povidone.

Please note: Inactive ingredients may vary between different brands of generic medication. Please read the Patient Information Leaflet provided for further information.

Which ingredients can cause an allergic reaction?

Serious allergic reactions to acetazolamide are infrequent. While there are some reports of adverse effects of acetazolamide, there is only one previous report of anaphylactic shock caused by the oral intake of acetazolamide. Signs of a severe allergic reaction requiring emergency medical attention include rash or hives, chest tightness, shortness of breath, trouble breathing and dizziness.