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Carbonic anhydrase inhibitors used in the management of open angle glaucoma include dorzolamide (a topical agent) and acetazolamide (oral and intravenous preparation).
These agents act on carbonic anhydrase isoenzyme II in the ciliary body and result in a reduction in aqueous production by decreasing bicarbonate secretion into the posterior chamber by ciliary epithelial cells. Their actions last for 6-12 hours and so are primarily a short term agent e.g. dorzolamide is given three times daily.
Oral carbonic anhydrase inhibitors are generally used only in acute management of raised intraocular pressure but, occasionally, can be used chronically as a last resort.
Possible side effects include paraesthesia, general malaise, diuresis, renal calculi, and metabolic acidosis.
Carbonic anhydrase inhibitors are additive to other drugs e.g. dorzolamide only needs to be taken twice daily when used in combination with a beta-blocker (1).
There is no additional lowering of intraocular pressure if a topical carbonic anhydrase inhibitor is added to a systemic one.
These agents should be avoided in pregnancy.
The summary of product characteristics should be consulted before prescribing a topical carbonic anhydrase inhibitor.