Brinzolamide 1% w/v · Eye drops

Carbonic anhydrase is an enzyme found in many tissues of the body including the eye. It catalyzes the reversible reaction involving the hydration of carbon dioxide and the dehydration of carbonic acid. In humans, carbonic anhydrase exists as a number of isoenzymes, the most active being carbonic anhydrase II, found primarily in red blood cells (RBCs), but also in other tissues. Inhibition of carbonic anhydrase 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. The result is a reduction in IOP.

Brinzolamide ophthalmic suspension contains brinzolamide, an inhibitor of carbonic anhydrase II. Following topical ocular administration, brinzolamide inhibits aqueous humor formation and reduces elevated IOP. Elevated IOP is a major risk factor in the pathogenesis of optic nerve damage and glaucomatous visual field loss.

Following topical ocular administration, brinzolamide is absorbed into the systemic circulation. Due to its affinity for carbonic anhydrase II, brinzolamide distributes extensively into the RBCs and exhibits a long half-life in whole blood (approximately 111 days). In humans, the metabolite N-desethyl brinzolamide is formed, which also binds to carbonic anhydrase and accumulates in RBCs. This metabolite binds mainly to carbonic anhydrase I in the presence of brinzolamide. In plasma, both parent brinzolamide and N-desethyl brinzolamide concentrations are low and generally below assay quantitation limits (less than 10 ng/mL). Binding to plasma proteins is approximately 60%. Brinzolamide is eliminated predominantly in the urine as unchanged drug. N-Desethyl brinzolamide is also found in the urine along with lower concentrations of the N-desmethoxypropyl and O-desmethyl metabolites.

An oral pharmacokinetic study was conducted in which healthy volunteers received 1 mg capsules of brinzolamide twice per day for up to 32 weeks. This regimen approximates the amount of drug delivered by topical ocular administration of brinzolamide ophthalmic suspension dosed to both eyes 3 times per day and simulates systemic drug and metabolite concentrations similar to those achieved with long-term topical dosing. Red blood cell carbonic anhydrase activity was measured to assess the degree of systemic carbonic anhydrase inhibition. Brinzolamide saturation of RBC carbonic anhydrase II was achieved within 4 weeks (RBC concentrations of approximately 20 mcM). N-Desethyl brinzolamide accumulated in RBCs to steady-state within 20 to 28 weeks reaching concentrations ranging from 6 to 30 mcM. The inhibition of carbonic anhydrase II activity at steady state was approximately 70% to 75%, which is below the degree of inhibition expected to have a pharmacological effect on renal function or respiration in healthy subjects.