Acetazolamide (Diamox SR)
Is It Right for You?
A complete guide to Acetazolamide (Diamox SR) — what it treats, how it works, dosages, side effects, and when a clinician may prescribe it following an online consultation.
What Is Acetazolamide (Diamox SR)?
Acetazolamide, marketed in its sustained-release formulation as Diamox SR, is a carbonic anhydrase inhibitor with a broad range of clinical applications including the prevention and treatment of altitude sickness, the management of certain epilepsy syndromes, glaucoma, and idiopathic intracranial hypertension (IIH). It was one of the first clinically used diuretics and remains a uniquely versatile agent.
Diamox SR is a sustained-release capsule containing 250 mg of acetazolamide, designed to provide prolonged drug release and allow twice-daily dosing. Standard immediate-release acetazolamide tablets (250 mg) are also available for indications requiring more flexible dosing. The sustained-release formulation is particularly favoured for altitude sickness prophylaxis and glaucoma management due to its convenience and consistent plasma levels.
Acetazolamide acts by inhibiting the enzyme carbonic anhydrase throughout the body — in the renal tubules, ciliary body of the eye, choroid plexus of the brain, and erythrocytes — producing its clinically diverse range of effects from a single mechanism.
Acetazolamide is a prescription-only medication in the UK. A licensed clinician must assess your medical history, sulfonamide allergy status, renal and hepatic function, and electrolyte profile before it can be prescribed.
What Conditions Is Acetazolamide Used For?
Acetazolamide is Used For
prevention and early treatment of symptoms of acute mountain sickness (AMS), including headache, nausea, dizziness, and fatigue at high altitude
reduction of intraocular pressure in open-angle glaucoma and pre-operatively in angle-closure glaucoma; typically as adjunct therapy
reduction of cerebrospinal fluid production to lower intracranial pressure; first-line pharmacological treatment in IIH
adjunctive treatment in certain seizure types, including absence seizures and catamenial (menstrually-related) epilepsy, particularly where other agents have been inadequate
historically used as a diuretic; now rarely used for this indication given the availability of more effective agents
In altitude sickness, acetazolamide facilitates acclimatisation but does not replace the need for gradual ascent and descent if symptoms are severe. In IIH, it reduces intracranial pressure but does not address the underlying cause; weight management (where relevant) and ophthalmological monitoring remain essential. In epilepsy, tolerance to the antiepileptic effect may develop over time.
How Does Acetazolamide Work?
Acetazolamide inhibits the enzyme carbonic anhydrase, which catalyses the reversible reaction between carbon dioxide and water to form carbonic acid and subsequently bicarbonate and protons (CO₂ + H₂O ⇌ HCO₃⁻ + H⁺). This seemingly simple enzymatic blockade has far-reaching physiological consequences depending on the tissue in which it acts:
Renal tubules — inhibition of carbonic anhydrase in the proximal tubule reduces bicarbonate reabsorption, resulting in increased urinary excretion of bicarbonate, sodium, and water. This produces a mild diuresis and a metabolic acidosis. In altitude sickness, this metabolic acidosis stimulates compensatory hyperventilation, raising arterial oxygen tension and accelerating acclimatisation.
Choroid plexus (brain) — carbonic anhydrase is essential for cerebrospinal fluid (CSF) production. Inhibition reduces CSF secretion by up to 50%, thereby lowering intracranial pressure — the principal mechanism in IIH.
Ciliary body (eye) — aqueous humour production in the eye is carbonic anhydrase-dependent. Inhibition reduces intraocular pressure, providing benefit in glaucoma.
Neuronal membranes — the mechanism of antiepileptic action is less fully characterised but is thought to involve neuronal hyperpolarisation secondary to intracellular acidosis and direct effects on neuronal excitability, reducing seizure threshold.
Dosages & Administration
The correct dose depends on the type and severity of infection, age, weight, and kidney function. Always follow your clinician's instructions. The table below is for general reference only.
Administration Tips
Take Diamox SR at the same times each day. The sustained-release formulation provides more consistent plasma levels than immediate-release tablets and is better suited to twice-daily dosing regimens.
Can be taken with food if gastrointestinal side effects are troublesome. Food slightly delays absorption but does not significantly affect bioavailability.
Maintain adequate hydration. Acetazolamide is a mild diuretic and increases the risk of renal calculi; patients should drink sufficient fluid throughout the day, particularly in warm climates or during physical activity.
Do not crush or chew Diamox SR capsules. The sustained-release pellets must be swallowed intact. If difficulty swallowing, the capsule may be opened and the pellets sprinkled onto a small amount of soft food, but they must not be chewed.
For altitude sickness prophylaxis, begin one to two days before planned ascent to allow plasma levels to reach steady state. Discontinue two days after reaching the highest planned altitude or upon return to low altitude.
Potassium supplementation may be required with long-term use due to urinary potassium wasting; your clinician will monitor electrolytes.
Side Effects of Acetazolamide
Common Side Effects
- Paraesthesia — tingling or numbness of the fingers, toes, and perioral area; extremely common (>50% of users); caused by metabolic acidosis; benign and usually does not require discontinuation
- Increased urinary frequency — due to diuretic effect; particularly noticeable at initiation
- Nausea, vomiting, or loss of appetite
- Dysgeusia — altered taste, particularly for carbonated beverages (carbonic acid is broken down, making fizzy drinks taste flat)
- Fatigue or malaise
- Polyuria and polydipsia
- Mild metabolic acidosis — usually asymptomatic but may manifest as fatigue or mild breathlessness
- Severe allergic reaction / anaphylaxis — acetazolamide is a sulfonamide derivative; there is a theoretical cross-reactivity risk in patients with sulfonamide allergy, though the clinical significance is debated; urticaria, angioedema, bronchospasm
- Stevens-Johnson Syndrome / toxic epidermal necrolysis — rare but life-threatening; skin blistering, mucous membrane involvement, fever
- Severe metabolic acidosis — particularly in patients with renal impairment, the elderly, or those on concurrent medications that lower bicarbonate; confusion, rapid breathing, lethargy
- Agranulocytosis or aplastic anaemia — rare haematological reactions; unexplained fever, mouth ulcers, bruising, or unusual bleeding
- Nephrolithiasis (kidney stones) — alkaline urine and hypercalciuria from acetazolamide promote calcium phosphate stone formation; flank pain, haematuria
- Severe hypokalaemia — weakness, palpitations, muscle cramps; risk increased with concurrent diuretic use
- Hepatic failure — rare; jaundice, abdominal pain, dark urine
Tingling in the extremities and around the mouth is experienced by the majority of patients and reflects acetazolamide's intended pharmacological effect of inducing a mild metabolic acidosis. While benign, it can be distressing to patients who are not forewarned. Clinicians should counsel patients that this is expected, not dangerous, and typically diminishes with continued use. Severe acidosis requiring discontinuation is uncommon in patients with normal renal function.
Drug Interactions
Always disclose all prescription drugs, over-the-counter medicines, vitamins, and supplements to your clinician or pharmacist before starting Acetazolamide.
Acetazolamide promotes renal lithium excretion, reducing plasma lithium levels. Conversely, metabolic acidosis from acetazolamide can alter lithium handling unpredictably. Monitor lithium levels closely at initiation and following dose changes.
Concurrent use significantly increases the risk of acetazolamide toxicity, including metabolic acidosis and CNS effects (confusion, lethargy, coma); the combination should be avoided or used only with close monitoring.
Additive risk of metabolic acidosis, nephrolithiasis, and hyperthermia. The combination should generally be avoided or used with careful monitoring.
Acetazolamide alkalinises the urine, altering the renal clearance of certain antifolates. Monitor for toxicity.
Acetazolamide can impair glycaemic control; blood glucose monitoring should be intensified in diabetic patients.
Acetazolamide-induced hypokalaemia can potentiate digoxin toxicity; monitor electrolytes and digoxin levels.
Additive diuretic and electrolyte-depleting effects; risk of hypotension and hypokalaemia. Monitor blood pressure and electrolytes.
Acetazolamide may increase phenytoin levels; monitor for signs of phenytoin toxicity (nystagmus, ataxia, confusion).
Important Warnings
Acetazolamide is structurally related to sulfonamide antibiotics. Although true cross-reactivity is uncommon and debated, patients with a history of severe sulfonamide reactions (particularly Stevens-Johnson Syndrome or anaphylaxis) should be prescribed acetazolamide with caution and only after careful clinical assessment. Inform your clinician of any prior sulfonamide or sulphur drug reactions.
Acetazolamide is contraindicated in severe renal impairment (the drug depends on renal excretion and may accumulate, worsening acidosis) and in severe hepatic impairment (risk of hepatic encephalopathy due to reduced ammonia clearance). Dose adjustment and closer monitoring are required in mild-to-moderate impairment.
Acetazolamide alkalinises the urine and promotes calciuria, creating conditions favourable for calcium phosphate stone formation. Patients with a personal or family history of nephrolithiasis should be made aware of this risk. Maintaining adequate hydration significantly reduces stone risk during treatment.
Long-term acetazolamide use can cause progressive hypokalaemia and metabolic acidosis. Baseline and periodic monitoring of serum electrolytes, bicarbonate, and renal function is recommended, particularly in patients on other diuretics, those with comorbidities, and the elderly.
Acetazolamide is teratogenic in animal studies and should be avoided in pregnancy, particularly in the first trimester. It is used in IIH during pregnancy only in exceptional circumstances and under specialist guidance, given the potentially serious risks of undertreated intracranial hypertension. Breastfeeding is not recommended during treatment.
Elderly patients are at higher risk of metabolic acidosis, electrolyte disturbances, and falls secondary to increased urinary frequency and diuresis. Lower starting doses and more frequent electrolyte monitoring are advisable in this group.
Speak to a Clinician About Treatment
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The treatment you need, when you need it.
Acetazolamide (Diamox SR) FAQs
Tingling or numbness in the fingers, toes, and around the mouth — known as paraesthesia — is one of the most common and predictable effects of acetazolamide. It is caused by the mild metabolic acidosis the drug intentionally induces. It is not dangerous and typically improves with continued use. If it is severe or distressing, speak with your clinician.
Alcohol should be avoided or minimised. It can worsen the diuretic effect of acetazolamide, compound metabolic acidosis, increase the risk of dehydration, and potentially impair judgement — all of which are particularly relevant at high altitude where acetazolamide is often used.
Acetazolamide significantly reduces the incidence and severity of acute mountain sickness when used correctly. However, it does not guarantee protection, and the most reliable prevention strategy remains a gradual ascent with adequate acclimatisation time. It should be seen as a us
Acetazolamide inhibits carbonic anhydrase on the tongue, which breaks down carbonic acid in carbonated drinks. Without this enzymatic activity, the acidic taste and carbonation of fizzy drinks is altered — they often taste flat or unpleasant. This is a harmless and reversible effect.
This requires discussion with your clinician. Acetazolamide is a sulfonamide-derived drug, and while true immunological cross-reactivity with sulfonamide antibiotics is uncommon, a history of severe sulfonamide reactions is a relative contraindication. Your clinician will weigh the risks and benefits on an individual basis.
Reduction in intracranial pressure typically begins within days of starting treatment, though the full clinical benefit — including improvement in headache, visual symptoms, and papilloedema — may take weeks to months to become fully apparent at therapeutic doses.