Makindo Medical Notes

⚠️ Adverse reactions: Sulphonamides carry a risk of Stevens–Johnson syndrome, toxic epidermal necrolysis, fulminant hepatic necrosis, agranulocytosis, and aplastic anaemia. Monitor closely for rash, cytopenia, or hepatic dysfunction, particularly in long-term use.

📘 About: Always check the BNF link here

• Acetazolamide is a carbonic anhydrase inhibitor and a sulphonamide derivative.
• It acts primarily in the proximal renal tubule, inhibiting bicarbonate reabsorption and promoting mild diuresis with urinary alkalinisation.
• Also reduces aqueous humour formation in the eye and cerebrospinal fluid (CSF) secretion in the choroid plexus.

⚙️ Mechanism of Action

• Inhibition of carbonic anhydrase decreases the conversion of carbonic acid to CO₂ and water.
• This leads to loss of bicarbonate (HCO₃⁻) in urine, metabolic acidosis, and mild diuresis.
• In the eye, reduced aqueous humour lowers intraocular pressure — useful in glaucoma.
• At altitude, it induces a mild metabolic acidosis, stimulating ventilation and improving oxygenation.

🎯 Indications & Dosing

• Primary open-angle glaucoma
• Altitude sickness prophylaxis
• Raised intracranial pressure (ICP) / idiopathic intracranial hypertension
• Epilepsy (especially absence/petit mal, adjunctive use)
• Congestive cardiac failure (for diuresis when resistant to loop diuretics)

💊 Common Adult Doses (Check BNF for confirmation)

⚠️ Contraindications

• Known sulphonamide allergy
• Metabolic or respiratory acidosis
• Severe hepatic impairment (risk of hepatic encephalopathy)
• Hyponatraemia or hypokalaemia
• Addison’s disease or marked adrenocortical insufficiency

💥 Side Effects

• Paraesthesia (tingling in extremities), fatigue, drowsiness
• Loss of appetite, nausea, or taste disturbance
• Polyuria, thirst, metabolic acidosis
• Depression, irritability, or confusion
• Extravasation if given IV → skin necrosis
• Rare: bone marrow suppression, hypersensitivity rash, hepatic dysfunction

🔄 Interactions

• May increase plasma levels of carbamazepine.
• Enhances cardiotoxicity of flecainide, lidocaine, digoxin, and disopyramide.
• Reduces lithium levels (due to enhanced renal clearance).
• Potentiates acidosis with other carbonic anhydrase inhibitors or high-dose salicylates.

🧠 Teaching Point

Acetazolamide illustrates how renal physiology links to multiple systems: by reducing bicarbonate reabsorption, it alters CSF and aqueous humour dynamics as well as systemic acid–base balance. Its effect on ventilation in altitude sickness is due to a mild metabolic acidosis driving compensatory hyperventilation — a neat physiological feedback mechanism to improve oxygenation at altitude.

📚 References

• BNF: Acetazolamide
• NICE CKS: Glaucoma Management
• Acetazolamide in idiopathic intracranial hypertension (NEJM 2017)