Dorzolamide Hydrochloride Timolol Maleate

For the treatment of open-angle glaucoma or ocular hypertension, the standard adult dosage of dorzolamide 2% ophthalmic solution is:

• One drop in the affected eye(s) three times daily (TID).

When dorzolamide is used as an adjunctive therapy (added to another glaucoma medication like a beta-blocker), the dosage is typically one drop twice daily (BID). However, your ophthalmologist (eye specialist) will determine the exact frequency based on your intraocular pressure (IOP) response. Clinical trials have demonstrated that the three-times-daily regimen provides the most consistent pressure-lowering effect throughout a 24-hour period.

Dorzolamide has been studied in pediatric patients. For children with glaucoma or elevated IOP, the dosage is generally the same as the adult dosage:

• One drop in the affected eye(s) three times daily.

Safety and efficacy have been established in children as young as infants, though it is used with caution. Pediatric patients should be monitored closely for systemic side effects, particularly if they are also taking oral carbonic anhydrase inhibitors.

Renal Impairment

Dorzolamide is primarily excreted by the kidneys. Because the drug and its metabolites can accumulate in the setting of kidney disease, dorzolamide is not recommended for patients with severe renal impairment (Creatinine Clearance < 30 mL/min). There are no specific dose adjustments for mild to moderate renal impairment, but caution is advised.

Hepatic Impairment

Dorzolamide has not been extensively studied in patients with hepatic (liver) impairment. Because the drug is metabolized in the liver, it should be used with caution in patients with known liver disease.

Elderly Patients

No overall differences in safety or effectiveness have been observed between elderly and younger patients. Dosage remains the standard 2% solution TID.

Proper administration is crucial to ensure the medication reaches the eye and to minimize systemic absorption:

1. 1Wash your hands thoroughly before use.
2. 2Tilt your head back and pull down the lower eyelid to create a small pocket.
3. 3Hold the dropper above the eye without touching the eye, eyelid, or any other surface to prevent contamination.
4. 4Squeeze one drop into the pocket.
5. 5Close your eye gently and press your finger against the inner corner of the eye (near the nose) for 1 to 2 minutes. This technique, called punctal occlusion, prevents the medicine from draining into the tear duct and entering the bloodstream.
6. 6Wait at least 5 to 10 minutes before applying any other eye drops. This prevents the second drop from washing out the dorzolamide.
7. 7If you wear contact lenses

If you miss a dose, apply it as soon as you remember. However, if it is almost time for your next scheduled dose, skip the missed dose and return to your regular dosing schedule. Do not apply a double dose to make up for a missed one. Maintaining a consistent schedule is vital for controlling eye pressure.

While systemic overdose from topical ophthalmic use is unlikely, accidental ingestion or excessive use can occur. Symptoms of systemic CAI overdose may include electrolyte imbalance, development of an acidotic state (metabolic acidosis), and potential central nervous system effects (dizziness, fatigue). In the event of an overdose, seek emergency medical attention or contact a poison control center immediately. Treatment is typically supportive, focusing on maintaining electrolyte balance.

> Important: Follow your healthcare provider's dosing instructions exactly. Do not adjust your dose or stop using the medication without medical guidance, as this can lead to a dangerous spike in eye pressure.

The most frequently reported side effect of dorzolamide is a bitter, sour, or unusual taste (dysgeusia) in the mouth shortly after application. This occurs because the medication drains through the tear ducts into the throat.

Other very common effects include:

• Ocular Burning and Stinging: A transient (temporary) sharp sensation immediately after the drop is instilled. This usually lasts for 30 to 60 seconds.
• Blurred Vision: Temporary cloudiness or haziness of vision immediately after application.
• Ocular Hyperemia: Redness of the white part of the eye (conjunctiva).

These effects may occur in a significant minority of patients and should be monitored:

• Superficial Punctate Keratitis: Small areas of cell loss on the surface of the cornea, which may cause a 'gritty' feeling.
• Tearing (Epiphora): Increased production of tears.
• Eyelid Inflammation (Blepharitis): Redness, swelling, or crusting of the eyelids.
• Eye Itching (Pruritus): A persistent urge to rub the eyes.
• Headache: Mild to moderate aching in the forehead or temple region.
• Asthenia/Fatigue: A general feeling of tiredness or lack of energy.

• Iridocyclitis: Inflammation of the iris and ciliary body.
• Corneal Edema: Swelling of the cornea, particularly in patients with low endothelial cell counts.
• Dizziness and Paresthesia: A tingling sensation in the hands or feet (rare with topical use but possible).
• Urticaria: Hives or skin rash.

While rare, some side effects require urgent medical intervention.

> Warning: Stop taking Dorzolamide and call your doctor immediately if you experience any of these:

1. 1Severe Allergic Reactions: Signs include swelling of the face, lips, tongue, or throat; difficulty breathing; or severe skin rashes. Because dorzolamide is a sulfonamide, it can cause the same severe reactions as 'sulfa' drugs.
2. 2Stevens-Johnson Syndrome (SJS): A rare but life-threatening skin condition characterized by flu-like symptoms followed by a painful red or purplish rash that spreads and blisters.
3. 3Toxic Epidermal Necrolysis (TEN): A more severe form of SJS involving extensive skin peeling.
4. 4Bacterial Keratitis: Severe eye pain, sudden vision changes, or discharge, often caused by contaminating the dropper bottle.
5. 5Corneal Decompensation: Persistent clouding of the cornea that does not clear up, which may lead to permanent vision loss if not addressed.

Prolonged use of dorzolamide is generally well-tolerated. However, long-term exposure to the preservative benzalkonium chloride (found in many multi-dose bottles) can lead to Dry Eye Syndrome or ocular surface disease. Patients on long-term therapy should have their corneal health monitored regularly. There is also a theoretical risk of systemic accumulation in red blood cells, though clinical consequences of this in patients with healthy kidneys are negligible.

There are currently no FDA black box warnings for dorzolamide ophthalmic solution. However, the labeling contains significant warnings regarding its sulfonamide nature and the potential for severe hypersensitivity reactions.

Report any unusual symptoms or persistent irritation to your healthcare provider. If you develop an eye infection or sustain an eye injury, consult your doctor immediately regarding the continued use of your multi-dose bottle.

Dorzolamide is a sulfonamide (a 'sulfa' drug). Although it is applied topically, it is absorbed systemically. Therefore, the same types of adverse reactions that are attributable to sulfonamides may occur with dorzolamide. This includes the risk of severe skin reactions and blood disorders. Patients should be aware that if they have a known allergy to sulfa medications, they are at a higher risk of reacting to dorzolamide.

No FDA black box warnings for Dorzolamide.

• Allergic Reactions / Anaphylaxis Risk: Fatalities have occurred, although rarely, due to severe reactions to sulfonamides. If signs of serious reactions or hypersensitivity occur (e.g., skin rash, wheezing, swelling), discontinue the use of this preparation immediately.
• Corneal Endothelium Health: Carbonic anhydrase is necessary for the proper function of the corneal endothelium (the inner layer of the cornea that keeps it clear). Patients with low endothelial cell counts or pre-existing corneal defects are at an increased risk of developing corneal edema (swelling) while using dorzolamide.
• Bacterial Keratitis: There have been reports of bacterial keratitis (infection of the cornea) associated with the use of multiple-dose containers of topical ophthalmic products. These containers had been inadvertently contaminated by patients who, in most cases, had a concurrent corneal disease or a disruption of the ocular epithelial surface.
• Acute Angle-Closure Glaucoma: Dorzolamide is not typically used as the primary treatment for acute angle-closure glaucoma, which requires immediate medical intervention to lower pressure and often surgical or laser treatment.

Patients using dorzolamide should undergo regular ophthalmic monitoring, including:

• Intraocular Pressure (IOP) Measurements: To ensure the drug is effectively controlling the pressure.
• Visual Field Testing: To check for any progression of glaucoma-related damage.
• Slit-Lamp Examinations: To monitor the health of the cornea and conjunctiva.
• Electrolyte Monitoring: Generally not required for topical use, but may be considered in patients with severe renal disease or those also taking oral CAIs.

Dorzolamide may cause temporary blurred vision immediately after application. Do not drive, operate heavy machinery, or perform hazardous activities until your vision is clear. If you experience persistent dizziness or fatigue, consult your doctor.

There are no known direct interactions between alcohol and dorzolamide. However, alcohol can sometimes affect eye pressure and general hydration. It is best to consume alcohol in moderation while being treated for glaucoma.

Do not stop using dorzolamide abruptly unless directed by your doctor. Glaucoma is often a 'silent' disease with no symptoms until vision is lost. Stopping the medication can result in a rapid increase in intraocular pressure, which can cause irreversible damage to the optic nerve. There is no 'withdrawal syndrome,' but the return of high IOP is a significant risk.

> Important: Discuss all your medical conditions, especially kidney disease, liver disease, or sulfonamide allergies, with your healthcare provider before starting Dorzolamide.

• Oral Carbonic Anhydrase Inhibitors (e.g., Acetazolamide, Methazolamide): The use of dorzolamide with oral CAIs is generally not recommended. There is a potential for an additive effect on the known systemic effects of carbonic anhydrase inhibition (such as electrolyte imbalance or metabolic acidosis). Since the benefit of adding a topical CAI to an oral one is minimal, this combination should be avoided.

• High-Dose Salicylates (e.g., Aspirin > 2g/day): Although not reported with topical dorzolamide, oral CAIs have been known to interact with high-dose aspirin. This can lead to central nervous system toxicity and metabolic acidosis. While the systemic levels of dorzolamide are low, caution is advised in patients taking large doses of aspirin for conditions like rheumatoid arthritis.

• Other Ophthalmic Medications: If you are using multiple eye drops, they must be spaced out. Using them too close together can cause 'washout,' where the second drop flushes the first drop out of the eye before it can be absorbed. Wait at least 5 to 10 minutes between different medications.
• Silver-containing products: Some topical ophthalmic products containing silver (rarely used today) may interact with the sulfonamide structure of dorzolamide.

There are no known specific food interactions with dorzolamide. Unlike some oral medications, its absorption is not affected by diet because it is applied topically. However, maintaining a consistent intake of potassium-rich foods is generally good practice for patients at risk of electrolyte shifts, though this risk is negligible with topical dorzolamide.

• St. John’s Wort: While primarily an inducer of liver enzymes (CYP3A4), there is no evidence it significantly affects the levels of topically applied dorzolamide.
• Diuretic Herbs: Herbs with diuretic properties (like dandelion or juniper) could theoretically contribute to electrolyte changes if systemic absorption of dorzolamide is high, though this is clinically unlikely.

Dorzolamide is not known to interfere with common laboratory tests. However, because it is a sulfonamide, it could theoretically interfere with certain tests for urinary protein or glucose that use older chemical methods, though modern enzymatic tests are unaffected.

For each major interaction, the primary concern is the potential for systemic accumulation or additive pharmacological effects. In the case of oral CAIs, the mechanism is pharmacodynamic (both drugs hitting the same target), leading to increased risk of systemic acidosis. Management involves avoiding the combination or choosing an alternative class of glaucoma medication (like a prostaglandin analog).

> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking, including over-the-counter eye washes or allergy drops.

Conditions where Dorzolamide must NEVER be used include:

1. 1Hypersensitivity to Dorzolamide: Any patient with a documented history of severe allergic reaction (anaphylaxis, angioedema) to dorzolamide or any component of the formulation (such as the preservative benzalkonium chloride) must not use the drug.
2. 2Hypersensitivity to Sulfonamides: Because dorzolamide is a sulfonamide derivative, it is contraindicated in patients with a history of severe hypersensitivity to 'sulfa' drugs. Cross-reactivity can lead to life-threatening skin reactions like Stevens-Johnson Syndrome.
3. 3Severe Renal Impairment: Patients with a Creatinine Clearance (CrCl) of less than 30 mL/min should not use dorzolamide. The drug and its metabolites are cleared by the kidneys, and in severe impairment, they can accumulate to toxic levels in the blood, potentially causing systemic metabolic acidosis.

Conditions requiring careful risk-benefit analysis by a physician:

• Hepatic Impairment: Since dorzolamide is metabolized by the liver, patients with significant liver disease should be monitored closely, as the drug's clearance may be altered.
• Pre-existing Corneal Defects: Patients with compromised corneal endothelial function (e.g., Fuchs' dystrophy) are at higher risk for corneal swelling and should be monitored with regular pachymetry (measuring corneal thickness).
• History of Kidney Stones: While more common with oral CAIs, there is a theoretical risk that dorzolamide could contribute to the formation of calcium phosphate stones in predisposed individuals due to changes in urinary pH.

As mentioned, the primary cross-sensitivity concern is with other sulfonamides. This includes certain antibiotics (like sulfamethoxazole), sulfonylureas (used for diabetes), and certain diuretics (like furosemide or thiazides). While many patients with a 'sulfa' allergy can tolerate these other classes, the risk with dorzolamide is considered high enough to warrant a contraindication in the setting of severe prior reactions.

> Important: Your healthcare provider will evaluate your complete medical history, including any past allergic reactions to antibiotics or other eye drops, before prescribing Dorzolamide.

FDA Pregnancy Category C.

There are no adequate and well-controlled studies of dorzolamide in pregnant women. In animal studies (rabbits), dorzolamide administered at doses that caused maternal toxicity (metabolic acidosis) resulted in skeletal malformations of the vertebral bodies.

• First Trimester: Use should be avoided unless the potential benefit justifies the potential risk to the fetus.
• Second and Third Trimesters: Continued use should be discussed with an obstetrician and ophthalmologist. High intraocular pressure must be managed to prevent maternal vision loss, but alternative treatments with better safety profiles may be considered.

It is not known whether dorzolamide is excreted in human milk. However, because many drugs are excreted in human milk and because of the potential for serious adverse reactions in nursing infants from dorzolamide, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother. If used, the mother should perform punctal occlusion (pressing the corner of the eye) to minimize systemic absorption.

The safety and effectiveness of dorzolamide have been established in pediatric patients. In a 3-month clinical study, the side effect profile in children was generally similar to that in adults. However, some children experienced higher rates of conjunctivitis and eyelid irritation. It is approved for use in children, but dosing should be strictly supervised by a parent or caregiver to ensure proper technique and prevent contamination.

A large percentage of patients treated for glaucoma are over the age of 65. Clinical data indicates that the efficacy and safety of dorzolamide are comparable between elderly patients and younger adults. However, elderly patients may be more likely to have age-related renal decline. Since the drug is contraindicated in severe renal impairment, kidney function should be considered when prescribing for very elderly or frail patients.

As noted, dorzolamide is not recommended for patients with a GFR or CrCl < 30 mL/min. In patients with mild to moderate impairment, no specific dose adjustment is required, but they should be monitored for signs of systemic CAI toxicity, such as unusual fatigue or metallic taste.

Because dorzolamide is metabolized by the liver, patients with Child-Pugh Class B or C impairment should be treated with caution. While no specific dosing guidelines exist, these patients should be monitored for any signs of increased systemic drug effects.

> Important: Special populations require individualized medical assessment. Always inform your doctor if you are planning a pregnancy or are currently breastfeeding.

Dorzolamide is a potent inhibitor of human carbonic anhydrase II (CA-II). Carbonic anhydrase (CA) 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 (CA-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 intraocular pressure (IOP). Dorzolamide is highly specific for CA-II and does not significantly inhibit other enzymes at therapeutic concentrations.

The onset of action for dorzolamide is typically within 60 to 90 minutes after a single dose. The peak effect occurs at approximately 2 hours, and the pressure-lowering effect is maintained for at least 8 to 12 hours. Unlike some other glaucoma medications, there is no evidence of tachyphylaxis (rapidly diminishing response) or significant tolerance development with long-term use of dorzolamide.

| Parameter | Value |

|---|---|

| Bioavailability | Low systemic levels; sequestered in RBCs |

| Protein Binding | Approximately 33% |

| Half-life (RBCs) | ~120 days |

| Tmax (Plasma) | N/A (Topical application) |

| Metabolism | Hepatic (N-desethyl metabolite) |

| Excretion | Renal (Parent and metabolite) |

• Molecular Formula: C10H16N2O4S3·HCl
• Molecular Weight: 360.91 g/mol
• Solubility: Soluble in water and slightly soluble in methanol and ethanol.
• Description: Dorzolamide hydrochloride is a white to off-white, crystalline powder. The ophthalmic solution is formulated to be iso-osmotic with a pH of approximately 5.6.

Dorzolamide is classified as a Carbonic Anhydrase Inhibitor. It is distinct from other glaucoma classes such as Prostaglandin Analogs (e.g., latanoprost), Beta-Blockers (e.g., timolol), and Alpha-Agonists (e.g., brimonidine). It is frequently used when these other classes are insufficient or inappropriate for the patient.