Dorzolamide / Timolol

Dorzolamide/timolol eye drops are used to lower elevated intraocular pressure (IOP) — pressure inside the eye — when treatment with a beta-blocker alone has not been sufficient.

• Open-angle glaucoma — a common form of glaucoma where fluid doesn't drain properly from the eye, causing pressure to build and potentially damaging the optic nerve
• Ocular hypertension — elevated eye pressure without other signs of glaucoma, which still raises the risk of optic nerve damage over time
• Cosopt and Cosopt PF are both approved for these uses; Cosopt PF and other preservative-free formulations are options specifically for patients who need to avoid preservatives in eye drops
• Safety and effectiveness have been established for pediatric patients aged 2 years and older

This combination drop lowers eye pressure using two complementary mechanisms. Dorzolamide blocks an enzyme called carbonic anhydrase II in the ciliary body (tissue inside the eye), slowing the production of aqueous humor — the fluid that normally circulates inside the eye. Timolol is a non-selective beta-adrenergic blocker that also reduces aqueous humor production by blocking receptors in the eye. Together, they achieve a greater reduction in eye pressure than either agent alone, helping to protect the optic nerve from pressure-related damage.

The standard dose is one drop in the affected eye or eyes, twice daily. If you are using other eye drops at the same time, allow at least 5 minutes between each one.

• For preservative-free single-use vials (such as Cosopt PF): open the unit just before use, apply to one or both eyes, and immediately discard the rest — do not store or reuse an opened unit
• Do not change your dosing schedule without talking to your prescriber first
• These drops can be used with or without food, as they are applied to the eye, not taken by mouth

Most people tolerate dorzolamide/timolol well, but some side effects are common:

• Bitter, sour, or unusual taste in the mouth (one of the most common, affecting up to 30% of users)
• Burning or stinging in the eye (also up to 30%)
• Red or bloodshot eyes
• Blurred or cloudy vision
• Eye itching or tearing
• Superficial punctate keratitis (minor irritation on the eye's surface)
• Headache, dizziness, or nausea
• Cough or upper respiratory symptoms

Serious reactions are less common but require prompt attention: severe breathing difficulty or wheezing, signs of heart failure, unusually slow heart rate, severe skin reactions (blistering or peeling), or any signs of a serious allergic reaction should prompt you to stop the drops and seek medical care immediately.

• Breathing risk: Timolol — even as an eye drop — is absorbed into the bloodstream and can cause severe bronchospasm or even death in people with asthma or severe COPD. This medication is contraindicated in those conditions.
• Heart risk: This medication can worsen heart failure or cause dangerously slow heart rates. It must not be used in people with sinus bradycardia, significant heart block, overt heart failure, or cardiogenic shock.
• Sulfonamide reactions: Dorzolamide is a sulfonamide drug. Rarely, sulfonamides cause life-threatening skin reactions (Stevens-Johnson syndrome), serious liver damage, or blood disorders. Stop using immediately and get medical help if you develop a severe rash, blistering, or jaundice.
• Diabetes and hypoglycemia: This medication can mask the warning signs of low blood sugar. People with diabetes using insulin or oral hypoglycemic agents should monitor carefully.
• Thyroid disease: Timolol can hide signs of an overactive thyroid (such as a fast heart rate). Do not stop this medication abruptly if you have thyroid disease.
• Allergy risk: People with a history of severe allergic reactions may respond less well to epinephrine (the standard treatment for anaphylaxis) while on beta-blockers.
• Surgery: Let your anesthesiologist know you are using this medication before any surgery, as it may affect responses to certain anesthetic agents.

Dorzolamide/timolol interacts with several types of medications because both ingredients can be absorbed into the bloodstream:

• Oral carbonic anhydrase inhibitors (e.g., acetazolamide) — not recommended together; additive systemic effects
• Other beta-blockers (oral or topical) — can amplify effects on heart rate and eye pressure; using two topical beta-blockers at once is not recommended
• Calcium channel blockers (oral or IV, e.g., verapamil) — risk of heart rhythm problems, reduced heart function, and low blood pressure, especially in people with heart disease
• Digitalis (digoxin) combined with calcium channel blockers — may further slow electrical conduction in the heart
• Catecholamine-depleting drugs (e.g., reserpine) — can cause very low blood pressure or severely slow heart rate
• CYP2D6 inhibitors (e.g., quinidine, many SSRIs) — can raise timolol blood levels, intensifying its effects on heart rate and potentially causing depression
• High-dose aspirin/salicylates — potential for electrolyte disturbances when combined with dorzolamide
• Clonidine — stopping clonidine while on a beta-blocker may worsen rebound high blood pressure

This is not a complete list of interactions. Always talk with your doctor or pharmacist before starting, stopping, or changing any medication.

• Do NOT use if you have asthma, a history of asthma, or severe COPD
• Do NOT use if you have sinus bradycardia (very slow heart rate), second- or third-degree heart block, overt heart failure, or cardiogenic shock
• Do NOT use if you have a known allergy to any component, including sulfonamide drugs
• Use with caution — or generally avoid — if you have mild-to-moderate COPD, bronchospastic lung disease, or any history of bronchospasm
• Tell your doctor if you have diabetes, especially if you take insulin or oral diabetes medications, as this drug can mask low blood sugar symptoms
• Tell your doctor if you have thyroid disease — abrupt discontinuation could trigger a dangerous thyroid event
• Tell your doctor if you have myasthenia gravis or muscle weakness conditions — timolol may worsen muscle weakness
• Pregnancy: no adequate human studies exist; discuss risks and benefits with your doctor
• Breastfeeding: it is not known if these drugs pass into breast milk; consult your doctor before using while nursing
• Children under 2: safety and effectiveness have not been established
• Severe kidney impairment: dorzolamide has not been adequately studied in this population; use with caution and under close medical supervision
• Hepatic (liver) impairment: use with caution as safety has not been established in this population

If too much of this medication is absorbed — whether from overuse of the drops or accidental ingestion — symptoms can include electrolyte imbalances, a dangerously acidic state in the blood, dizziness, headache, shortness of breath, very slow heart rate (bradycardia), bronchospasm, and potentially cardiac arrest. If you suspect an overdose, seek emergency medical help immediately. Note that timolol does not clear from the body easily through dialysis.

Both active ingredients in this combination work to reduce the production of aqueous humor (the fluid inside the eye), which directly lowers intraocular pressure. Elevated eye pressure is a major risk factor for optic nerve damage and progressive visual field loss — so reducing it helps protect vision over time. Using the two ingredients together produces a greater pressure-lowering effect than either one used alone, though the combination given twice daily is slightly less effective than using each ingredient separately at their individual full dosing schedules.

Even though these drops are applied to the eye, both ingredients are absorbed into the bloodstream. Dorzolamide accumulates in red blood cells during long-term use and is primarily excreted unchanged in the urine; after stopping, it clears from red blood cells slowly, with an elimination half-life of about four months. Timolol also reaches measurable levels in the blood — peak plasma levels occur after morning dosing with twice-daily use. Dorzolamide binds moderately to plasma proteins (about 33%) and is broken down into a metabolite that is also excreted in the urine.

Store Dorzolamide hydrochloride and Timolol maleate Ophthalmic Solution, USP (preservative free) at 20° to 25°C (68° to 77°F) . Do not freeze. Store in the original pouch.