Dorzolamide, a carbonic anhydrase inhibitor used to lower intraocular pressure in patients with glaucoma or ocular hypertension, was developed in the 1980s and approved for medical use in the mid-1990s. Its history is marked by its effectiveness in reducing intraocular pressure, often as part of combination therapy with other ocular medications, such as timolol. Dorzolamide is available as an ophthalmic solution and is generally well tolerated, though it can cause local side effects such as eye irritation or a bitter taste. Its development included extensive clinical trials to ensure safety and efficacy in lowering intraocular pressure, contributing significantly to modern glaucoma management.
BRAND NAMES
Trusopt – the most widely known brand for dorzolamide ophthalmic solution.
Cosopt – a combination of dorzolamide and timolol (used to treat glaucoma).
MECHANISM OF ACTION
Dorzolamide is a carbonic anhydrase inhibitor. It works by inhibiting the enzyme carbonic anhydrase in the ciliary body of the eye, which reduces the formation of bicarbonate ions. This leads to decreased sodium and fluid transport into the aqueous humor, ultimately lowering intraocular pressure (IOP).
PHARMACOKINETICS
Absorption
Dorzolamide is administered as an ophthalmic solution (eye drops). Only a small fraction of the drug is systemically absorbed through the conjunctiva and cornea. Peak plasma concentrations are very low, typically in the nanomolar range, due to limited systemic absorption. Most of the drug acts locally in the eye to reduce intraocular pressure.
Distribution
The apparent volume of distribution is estimated to be around 1–2 L/kg, reflecting this restricted distribution. Binding within erythrocytes acts as a reservoir, helping maintain low but sustained systemic levels despite the limited absorption from the eye.
Metabolism
Dorzolamide undergoes minimal systemic metabolism. After absorption into the bloodstream, most of the drug remains unchanged, with only a small portion converted into inactive metabolites.
Elimination
Dorzolamide is primarily eliminated unchanged by the kidneys. After systemic absorption, it is excreted in the urine, where a significant portion remains in its active form. The drug has a relatively long elimination half-life of approximately 4 months in red blood cells, due to its extensive binding to carbonic anhydrase in erythrocytes, which acts as a reservoir.
PHARMACODYNAMICS
Dorzolamide is a selective carbonic anhydrase inhibitor that reduces intraocular pressure (IOP) by decreasing aqueous humor production in the ciliary body. Inhibition of carbonic anhydrase slows the formation of bicarbonate ions, which in turn reduces the transport of sodium and fluid into the posterior chamber of the eye.
ADMINISTRATION
Dorzolamide is administered topically as an ophthalmic solution (eye drops). The usual dosage is one drop in the affected eye(s) two to three times daily, depending on the prescribing guidelines and whether it is used alone or in combination with other glaucoma medications.
DOSAGE AND STRENGTH
Dorzolamide is typically available as a 2% ophthalmic solution for topical use. The standard adult dose is one drop in the affected eye(s) two to three times daily. When used in combination with timolol (as in Cosopt), the dosing is usually one drop in the affected eye(s) twice daily. Pediatric dosing should be carefully adjusted under medical supervision.
DRUG INTERACTIONS
Dorzolamide has relatively few systemic drug interactions due to its minimal systemic absorption. However, caution is advised when it is used with other carbonic anhydrase inhibitors, such as acetazolamide, as additive effects can increase the risk of systemic metabolic acidosis.
FOOD INTERACTIONS
Dorzolamide has no significant food interactions because it is administered as a topical ophthalmic solution and has minimal systemic absorption. Its effectiveness in lowering intraocular pressure is not affected by meals or dietary intake, and patients can use the eye drops without regard to food.
CONTRAINDICATIONS
Dorzolamide is contraindicated in patients with known hypersensitivity to dorzolamide, other sulfonamide derivatives, or any component of the formulation. It should not be used in individuals with severe renal impairment or a history of sulfonamide-related allergic reactions, as systemic absorption—though minimal—could trigger adverse effects.
SIDE EFFECTS
Burning or stinging upon instillation
Eye irritation or discomfort
Blurred vision
Bitter or unusual taste in the mouth
Tearing or watery eyes
Dry eyes
OVER DOSAGE
Overdose of dorzolamide is uncommon due to its topical administration and minimal systemic absorption. In cases of accidental overuse, patients may experience increased ocular irritation, burning, or stinging, and rarely, systemic effects such as metabolic acidosis or electrolyte disturbances, especially in patients with predisposing conditions like renal impairment.
TOXICITY
Dorzolamide is generally considered to have a low systemic toxicity profile due to its topical administration and minimal systemic absorption. Local ocular toxicity may occur with excessive or prolonged use, including eye irritation, stinging, conjunctivitis, or corneal edema. Systemic toxicity is rare but may include metabolic acidosis, electrolyte imbalances, or hypersensitivity reactions, particularly in patients with renal impairment or sulfonamide allergies.
