A 58-year-old woman presents with acute angle-closure glaucoma. Which cholinergic agent is the most commonly used as first-line topical therapy for acute intraocular pressure reduction?

Explanation

## Cholinergic Agents in Acute Angle-Closure Glaucoma **Key Point:** Pilocarpine is the most commonly used direct-acting cholinergic (parasympathomimetic) agent for acute angle-closure glaucoma because of its potency, duration, and topical efficacy in reducing intraocular pressure (IOP). ### Mechanism of IOP Reduction Cholinergic agents cause **miosis** (pupil constriction) and **ciliary muscle contraction**, which: - Increases aqueous humor outflow through the trabecular meshwork. - Pulls the iris away from the angle, relieving obstruction in angle-closure glaucoma. - Reduces IOP within 15–30 minutes of instillation. ### Comparative Profile of Cholinergic Agents in Glaucoma | Drug | Type | Route | Onset | Duration | Clinical Use | Notes | |------|------|-------|-------|----------|--------------|-------| | **Pilocarpine** | Direct | Topical | 15–30 min | 4–8 hours | Acute angle-closure (first-line) | Most potent; excellent corneal penetration | | Acetylcholine | Direct | Topical (intraocular) | Immediate | <10 min | Intraoperative miosis only | Unstable; rarely used systemically | | Carbachol | Direct | Topical (intraocular) | Immediate | 4–6 hours | Intraoperative miosis | Resistant to acetylcholinesterase | | Bethanechol | Direct | Oral, SC | 30–60 min | 1–2 hours | Urinary retention; not for glaucoma | No ocular penetration; systemic only | ### Why Pilocarpine Is Preferred 1. **Topical efficacy:** Excellent corneal penetration; achieves therapeutic IOP reduction within 15–30 minutes. 2. **Duration:** 4–8 hours allows dosing 3–4 times daily; sufficient for acute management. 3. **Potency:** More potent than carbachol; lower concentrations required (1–4% solution). 4. **Safety:** Minimal systemic absorption when applied topically; muscarinic side effects are localized. **Clinical Pearl:** In acute angle-closure glaucoma, pilocarpine is used as **first-line medical therapy** alongside systemic agents (IV acetazolamide, IV mannitol) to lower IOP before definitive surgical intervention (laser peripheral iridotomy or surgical iridectomy). **High-Yield:** Acetylcholine is unstable in aqueous solution and is used only intraoperatively for immediate miosis during eye surgery. Carbachol is resistant to acetylcholinesterase degradation but is also primarily intraoperative. Bethanechol is a systemic agent for urinary retention and has no ocular penetration.