The first topical carbonic anhydrase inhibitor for clinical use Dorzolamide HCl (Axon 1517) has been prescribed widely for the treatment of glaucoma and ocular hypertension. It inhibits carbonic anhydrase II (CA-II; EC 4.2.1.1) selectively, which is the main CA iso-enzyme involved in aqueous humor secretion. Inhibition of CA-II in the ciliary processes of the eye decreases aqueous humor secretion, presumably by slowing the formation of bicarbonate ions with subsequent reduction in sodium and fluid transport. Dorzolamide also accumulates in red blood cells as a result of CA-II binding, as CA-II is found predominantly in erythrocytes. However, sufficient CA-II activity remains so that adverse effects due to systemic CA inhibition are not observed[1]. Membrane-associated carbonic anhydrase (CA, EC 4.2.1.1) IX (CA IX) is strongly overexpressed in a broad range of tumor types, and the expression of CA IX negatively correlates with the prognosis of cancer patients. In normal tissues CA IX expression is much more restricted with abundant expression mainly present in the mucosa of the glandular stomach[2].