Timolol (Ophthalmic)

• Open-Angle Glaucoma
• Ocular Hypertension
• Glaucoma Treatment

Timolol ophthalmic is a non-selective beta-adrenergic receptor blocking agent used to reduce elevated intraocular pressure (IOP) in patients with open-angle glaucoma or ocular hypertension. It remains one of the most commonly used first-line treatments for glaucoma.

Mechanism of Action

Timolol reduces intraocular pressure through beta-receptor blockade:

• Beta-receptor antagonism: Blocks both beta-1 and beta-2 receptors in the ciliary body
• Reduces aqueous humor production: Decreases secretion from ciliary epithelium
• No effect on outflow: Unlike some glaucoma drugs, does not affect trabecular or uveoscleral outflow
• IOP reduction: Typically lowers IOP by 20-30%

The exact mechanism by which beta-blockade reduces aqueous production is not completely understood.

Available Formulations

• Solution: 0.25%, 0.5% (Timoptic)
• Gel-forming solution: 0.25%, 0.5% (Timoptic-XE) - once daily dosing
• Preservative-free solution: 0.25%, 0.5% (Timoptic in Ocudose)
• Combination products: With dorzolamide (Cosopt), with brimonidine (Combigan)

Medical Uses

FDA-Approved Indications:

• Elevated intraocular pressure in patients with ocular hypertension
• Open-angle glaucoma

Dosing Guidelines

Solution (0.25% or 0.5%):

• One drop in affected eye(s) twice daily
• May start with 0.25% and increase if response inadequate

Gel-Forming Solution (0.25% or 0.5%):

• One drop in affected eye(s) once daily

Administration:

• Punctal occlusion (pressing on inner corner of eye) for 1-2 minutes after instillation reduces systemic absorption
• If using multiple eye drops, separate by at least 5 minutes

Important Safety Information

Contraindications:

• Bronchial asthma or history of asthma
• Severe chronic obstructive pulmonary disease
• Sinus bradycardia
• Second or third degree AV block
• Overt cardiac failure
• Cardiogenic shock
• Known hypersensitivity to timolol

Warnings and Precautions:

• Systemic absorption: Can cause systemic beta-blockade effects
• Respiratory effects: May cause bronchospasm; use with caution in mild COPD
• Cardiac effects: May mask signs of hypoglycemia and hyperthyroidism
• Abrupt withdrawal: May exacerbate angina if stopped suddenly
• Muscle weakness: May potentiate myasthenia gravis

Drug Interactions

• Oral beta-blockers: Additive systemic beta-blockade; monitor for hypotension and bradycardia
• Calcium channel blockers: Increased risk of AV block and hypotension
• Catecholamine-depleting drugs (reserpine): May cause additive hypotension
• Digitalis: Additive effects on cardiac conduction
• Quinidine: May potentiate beta-blockade
• CYP2D6 inhibitors (fluoxetine, paroxetine): May increase timolol levels

Special Populations

• Hepatic Impairment: No specific adjustment for ophthalmic use
• Renal Impairment: No specific adjustment for ophthalmic use
• Pregnancy: May cause fetal harm; use only if clearly needed
• Lactation: Present in breast milk; consider risk vs benefit
• Elderly: More susceptible to systemic effects
• Pediatric: Safety established for children; dose same as adults