This is the most widely prescribed carbonic anhydrase inhibitor. However, approximately 50% patients stop treatment with acetazolamide as a consequence of intolerable side effects due to extraocular inhibition of carbonic anhydrase. It reversibly blocks the enzyme carbonic anhydrase in the ciliary body and thus
suppresses aqueous humor production. The aqueous fluid rich in sodium and bicarbonate ions is hyperosmotic as compared to plasma. Water is attracted
to the posterior chamber as a result of osmosis and the high concentration of bicarbonate ions is diluted. When given orally, plasma levels attain a peak
at 2 hours, persisting for 4-6 hours and then rapidly drop because of urinary excretion. Acetazolamide is available as tablets and as capsules. The usual oral
dose is 125-250 mg four times daily. The effect of acetazolamide may be sustained by dispensing in 'coated granules form' and using an osmotic pump
delivery system48. Gastrointestinal upset is the most frequent symptom of acetazolamide intolerance. Severe side effects include myopia, pulmonary failure,
renal stones, aplastic anaemia, metabolic acidosis, hypersensitivity reactions and peripheral neuropathy.