The Development of Topically Acting Carbonic Anhydrase Inhibitors as Antiglaucoma Agents

Carbonic anhydrase inhibitors (CAIs) such as acetazolamide, methazolamide, ethoxzolamide and dichlorophenamide were and still are widely used systemic antiglaucoma drugs. Their mechanism of action consists in inhibition of CA isozymes present in ciliary processes of the eye (such as CA II, IV and XII), with the consequent reduction of bicarbonate and aqueous humour secretion, and of elevated intraocular pressure (IOP) characteristic of this disease. Since CA II/IV/XII are present in many other tissues/organs, generally, systemic CAIs possess undesired side effects such as numbness and tingling of extremities; metallic taste; depression; fatigue; malaise; weight loss; decreased libido; gastrointestinal irritation; metabolic acidosis; renal calculi and transient myopia. In order to avoid these undesired side effects, recently, topically effective CAIs have been developed. Two drugs are available clinically: dorzolamide and brinzolamide. Both these drugs are applied topically as water solutions/suspensions, alone or in combination with other agents (such as β- blockers, prostaglandin derivatives, etc) and produce a consistent and prolonged reduction of IOP. Furthermore, recent reports show both the systemically as well as topically acting sulfonamide CAIs to be effective in the treatment of macular oedema and other macular degeneration diseases, for which pharmacological treatment was unavailable up to now. Much research is in act in the search of even more effective topically acting CAIs, free of the inconveniences and side effects of the presently available drugs. For achieving this goal, a recently reported strategy, the tail approach, was extensively applied for the synthesis of large numbers of derivatives possessing various physico-chemical properties. Many such new sulfonamides showed promising antiglaucoma activity in animal models of the disease.