Acetazolamide

Eye pressure, altitude sickness and fluid retention

Acetazolamide lowers the pressure inside the eye. In glaucoma, where raised pressure can slowly damage sight, it works alongside eye drops or when drops alone are not enough. It also shortens and softens altitude sickness: the headache, nausea, dizziness, breathlessness and tiredness that come with climbing or flying to high ground too quickly. With other medicines it helps clear excess fluid in oedema and helps control seizures in some types of epilepsy.

How it works

The medicine blocks an enzyme called carbonic anhydrase, which normally helps move bicarbonate and water between tissues. In the eye that means less aqueous fluid is made, so the pressure inside drops. In the kidney, more water and salts leave in the urine, which is why acetazolamide counts as a mild diuretic (a water tablet). The same shift in the body's acid balance sits behind its use at altitude and in epilepsy.

Taking acetazolamide

Swallow the tablets with water. A trek or a flight to high ground calls for a course of only a few days, whereas glaucoma and fluid retention are usually managed for much longer. Drowsiness is possible and alcohol adds to it, so hold off driving or using machinery until you know how the tablets affect you. Skin burns more easily in strong sun while you take them, which makes sunscreen, a hat and sunglasses worth packing.

Side effects to expect

Stomach upset, nausea, loss of appetite and tiredness are usually the first things people notice. Tingling or numbness in the hands, feet or around the mouth is common, as are extra trips to the toilet and a metallic taste that makes fizzy drinks seem flat. Get help quickly for a rash or fever, a sore throat, unusual bleeding or bruising, blood or pain when passing urine, yellowing of the skin or eyes, confusion, or a seizure.

The Diamox listing

Diamox is the brand name for acetazolamide, sold here as 250mg tablets, the strength most adults are given. Acetazolamide is also made as ordinary capsules and as long-acting capsules, which are swallowed whole rather than crushed or chewed; the PockDose listing is the plain tablet. You will find it under Eye Care and Heart & Blood Pressure.