DIAMOX

What it is

DIAMOX is a tablet containing 250 mg acetazolamide. DIAMOX is a carbonic anhydrase inhibitor and a nonbacteriostatic sulfonamide that acts specifically on carbonic anhydrase, the enzyme that catalyses the reversible reaction involving the hydration of carbon dioxide and the dehydration of carbonic acid.

Approved indications

DIAMOX is indicated for adjunctive treatment of: — Oedema due to congestive heart failure — Drug-induced oedema — Centrencephalic epilepsies (petit mal, unlocalized seizures) — Chronic simple (open-angle) glaucoma — Secondary glaucoma — Acute angle-closure glaucoma preoperatively where delay of surgery is desired in order to lower intraocular pressure

Dosing overview

Dosing varies significantly by indication. For chronic simple (open-angle) glaucoma, dosage ranges from 250 mg to 1 g per 24 hours, usually in divided doses for amounts over 250 mg. For secondary glaucoma and preoperative treatment of acute angle-closure glaucoma, the preferred dosage is 250 mg every 4 hours, although some cases have responded to 250 mg twice daily on short-term therapy. For epilepsy, the recommended dose in paediatric patients is 8–30 mg/kg daily in divided doses not to exceed 750 mg per day, and in adults the recommended dose is 250–1000 mg daily in divided doses. For diuresis in congestive heart failure, the starting dose is usually 250 to 375 mg once daily in the morning. DIAMOX yields best diuretic results when given on alternate days, or for 2 days alternating with a day of rest. For drug-induced oedema, the recommended dosage is 250 to 375 mg once daily for 1 to 2 days, alternating with a day of rest.

Key safety warnings

Fatalities have occurred due to severe reactions to sulfonamides and sulphonamide derivatives, including acetazolamide. Adverse reactions common to all sulfonamide derivatives may occur: fever, rash (including erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis), fulminant hepatic necrosis, agranulocytosis, aplastic anaemia and other blood dyscrasias, anaphylaxis, renal and ureteral colic and renal lesions. Cases of choroidal effusion and detachment have been reported after the use of acetazolamide. Symptoms include acute onset of decreased visual acuity, blurred vision or ocular pain and can occur within hours to weeks after initiation of acetazolamide treatment. If choroidal effusion or detachment is suspected, acetazolamide should be discontinued as rapidly as possible. Severe cases of non-cardiogenic pulmonary oedema have been reported after taking acetazolamide, also after a single dose. Non-cardiogenic pulmonary oedema typically developed within minutes to hours after acetazolamide intake. Symptoms included dyspnoea, hypoxia, and respiratory insufficiency. If non-cardiogenic pulmonary oedema is suspected, acetazolamide should be withdrawn, and supportive treatment should be given. Suicidal ideation and behaviour have been reported in patients treated with anti-epileptic agents. A meta-analysis of randomised placebo controlled trials of anti-epileptic drugs has shown a small increased risk of suicidal ideation and behaviour. Patients should be monitored for signs of suicidal ideation and behaviours and appropriate treatment should be considered. Acetazolamide treatment may cause electrolyte imbalances, including hyponatraemia and hypokalaemia, as well as metabolic acidosis. Therefore, periodic monitoring of serum electrolytes is recommended.

Contraindications

Acetazolamide is contraindicated in the presence of hyperchloraemic acidosis, hypokalaemia, hyponatraemia, suprarenal gland failure, impairment of renal function with glomerular filtration rate less than 10 mL/min, and hypersensitivity to acetazolamide, sulfonamides, or sulfonamide derivatives, or any excipients in the formulation. Acetazolamide is contraindicated in marked liver disease or impairment of liver function, including cirrhosis, because of the risk of development of hepatic encephalopathy, as acetazolamide decreases ammonia clearance. It is contraindicated in severe glaucoma due to peripheral anterior synechias or in haemorrhagic glaucoma, and in long-term administration in patients with chronic noncongestive angle-closure glaucoma since it may permit organic closure of the angle to occur while the worsening glaucoma is masked by lowered intraocular pressure.

PBS listing

DIAMOX 250 mg tablet is listed on the PBS as a restricted item with an ex-manufacturer price of A$9.78.

Regulatory history

DIAMOX acetazolamide 250 mg tablet was first registered on the Australian Register of Therapeutic Goods on 9 September 1991.