How does apraclonidine work in angle closure glaucoma?

Mechanism of Apraclonidine in Angle Closure Glaucoma

Apraclonidine works in angle closure glaucoma primarily by reducing aqueous humor production through alpha-2 adrenergic receptor stimulation, which rapidly lowers intraocular pressure (IOP) during acute attacks and helps clear corneal edema to facilitate definitive treatment with laser peripheral iridotomy. 1

Pharmacological Mechanism

Apraclonidine is a relatively selective alpha-2-adrenergic agonist that has several effects on the eye:

• Primary mechanism: Reduces aqueous humor flow by stimulating the alpha-adrenergic system 1
• Onset of action: Usually noted within one hour
• Peak effect: Maximum IOP reduction occurs approximately three hours after instillation 1
• Magnitude of effect: Can reduce IOP by 20-30% when used as adjunctive therapy 2, 3

Role in Acute Angle-Closure Glaucoma Management

In acute angle-closure glaucoma (AACG), apraclonidine serves several critical functions:

1. Rapid IOP reduction: Helps quickly lower the dangerously elevated IOP during an acute attack 4
2. Corneal clearing: By reducing IOP, helps clear corneal edema, which is necessary for subsequent laser treatment 4
3. Perioperative use: Prevents IOP spikes during and after laser procedures 5

The American Academy of Ophthalmology recommends apraclonidine as one of several medications that can be used in the initial medical management of AACG, along with:

• Beta-adrenergic antagonists
• Carbonic anhydrase inhibitors (topical, oral, or intravenous)
• Hyperosmotic agents (oral or intravenous) 5, 4

Clinical Application in Angle Closure Glaucoma

Acute Management

• Used as part of initial medical therapy to rapidly lower IOP before definitive treatment with laser peripheral iridotomy (LPI) 4
• Particularly valuable when corneal edema is present, as it helps clear the cornea for subsequent laser treatment 5
• Brimonidine has been shown to be as effective as apraclonidine in preventing immediate IOP elevation after laser trabeculoplasty 5

Perioperative Use

• Effectively prevents IOP spikes after laser procedures such as laser peripheral iridotomy 5, 6
• Can be used before and after laser procedures to maintain stable IOP 5

Important Clinical Considerations

1. Limitations in ischemic conditions: When the ciliary body is ischemic due to extremely high IOP, agents that suppress aqueous humor formation (including apraclonidine) may initially have decreased effectiveness 4

2. Tachyphylaxis: The IOP-lowering efficacy of apraclonidine may diminish over time in some patients, making it more suitable for short-term rather than long-term use 1

3. Allergic reactions: Approximately 12-13% of patients may develop allergic-like reactions with continued use 1, 7

4. Adjunctive therapy: Most effective when used as part of a comprehensive treatment approach rather than as monotherapy 2, 7

Post-Iridotomy Considerations

After successful LPI, if IOP remains elevated, apraclonidine may be used as part of ongoing medical therapy. However, other factors that may contribute to persistent angle closure should be considered:

• Plateau iris syndrome
• Phacomorphic angle closure
• Secondary causes of angle closure
• Pre-existing open-angle glaucoma 5

In these cases, additional interventions beyond iridotomy may be necessary, and apraclonidine may serve as a temporary measure to control IOP while planning definitive treatment.