A 58-year-old man presents with elevated intraocular pressure (IOP) of 28 mmHg in both eyes and optic disc cupping. Gonioscopy shows open angles. Visual fields are normal. He has no contraindications to any class of glaucoma medications. What is the drug of choice for initiating monotherapy in primary open-angle glaucoma?

Explanation

## First-Line Monotherapy in POAG **Key Point:** Prostaglandin analogs (latanoprost, travoprost, bimatoprost) are the preferred first-line agents for primary open-angle glaucoma due to superior efficacy and once-daily dosing. ### Mechanism of Action Prostaglandin analogs increase uveoscleral (unconventional) outflow of aqueous humor, reducing IOP by 25–35%. ### Why Prostaglandin Analogs Are First-Line | Feature | Prostaglandin Analogs | Beta-Blockers | Carbonic Anhydrase Inhibitors | Alpha-2 Agonists | |---------|----------------------|----------------|-------------------------------|------------------| | **IOP Reduction** | 25–35% | 20–25% | 15–20% | 15–20% | | **Dosing Frequency** | Once daily (evening) | Twice daily | Twice–thrice daily | Twice–thrice daily | | **Systemic Side Effects** | Minimal | Bronchospasm, bradycardia, fatigue | Metabolic acidosis | Drowsiness, dry mouth | | **Local Side Effects** | Iris pigmentation, lash growth | Conjunctival hyperemia | Corneal edema | Conjunctival blanching | | **Contraindications** | Pregnancy (relative) | Asthma, COPD, heart block | Sulfonamide allergy | Monoamine oxidase inhibitors | **High-Yield:** Prostaglandin analogs are superior because they achieve the greatest IOP reduction with once-daily dosing and minimal systemic toxicity—ideal for compliance and patient tolerability. **Clinical Pearl:** Evening dosing of prostaglandin analogs is preferred because IOP is naturally higher in the morning; evening administration provides better 24-hour IOP control. **Mnemonic:** **PLAT** — **P**rostaglandin analogs are **L**arge reducers of **A**queous humor outflow (uveoscleral), **T**herapy of choice. ### Why Not Other Options? - **Beta-blockers (timolol):** Effective but second-line; require twice-daily dosing and carry systemic risks (contraindicated in asthma, COPD, bradycardia). - **Carbonic anhydrase inhibitors (dorzolamide):** Modest IOP reduction; reserved for adjunctive therapy or when prostaglandins contraindicated. - **Alpha-2 agonists (brimonidine):** Weak IOP reduction; used as adjunctive therapy; risk of tachyphylaxis with chronic use. [cite:Khurana 7e Ch 10]