## Correct Answer: C. Latanoprost Latanoprost is a **prostaglandin F2α analogue** that lowers intraocular pressure (IOP) by increasing uveoscleral outflow of aqueous humour. It is the safest choice in open-angle glaucoma complicated by bronchial asthma because it has **no systemic cardiovascular or respiratory effects**. Unlike non-selective beta-blockers (timolol), latanoprost does not cross the blood-brain barrier significantly and does not cause bronchospasm, making it ideal for asthmatic patients. Prostaglandin analogues are now first-line agents in glaucoma management across Indian guidelines (AIIMS, AIPG protocols) and are preferred in patients with contraindications to beta-blockers. Latanoprost is administered as a topical ophthalmic solution once daily in the evening, with excellent tolerability. The drug's mechanism—enhancing aqueous humour drainage rather than reducing production—avoids the systemic complications seen with other IOP-lowering agents in this clinical scenario. ## Why the other options are wrong **A. Mannitol infusion** — Mannitol is an **osmotic diuretic** that reduces IOP acutely by creating an osmotic gradient, but it is reserved for acute angle-closure glaucoma or perioperative use. It has no role in chronic open-angle glaucoma management and carries systemic risks (hyperglycaemia, dehydration, renal stress) unrelated to asthma. This is a distractor for students confusing acute vs. chronic glaucoma management. **B. Gemeprost** — Gemeprost is a **prostaglandin E1 analogue** used in obstetrics (medical abortion, cervical ripening) and gastroenterology, not ophthalmology. It has no IOP-lowering effect and is not indicated in glaucoma. This is a pure distractor testing whether students recognise the correct prostaglandin class for glaucoma (F2α analogues, not E1). **D. Timolol** — Timolol is a **non-selective beta-blocker** that effectively lowers IOP by reducing aqueous humour production, but it is **absolutely contraindicated in asthma** because it causes non-selective β2-adrenergic blockade, triggering bronchospasm and potentially fatal asthmatic exacerbation. This is the key discriminator in this question—the asthma comorbidity eliminates timolol despite its efficacy in glaucoma. ## High-Yield Facts - **Latanoprost** is a prostaglandin F2α analogue; first-line agent for open-angle glaucoma in India (AIPG guidelines). - **Prostaglandin analogues** increase uveoscleral (unconventional) aqueous humour outflow; no systemic respiratory or cardiovascular effects. - **Beta-blockers (timolol, betaxolol)** are contraindicated in asthma/COPD due to non-selective β2-blockade causing bronchospasm. - **Osmotic diuretics (mannitol, IV acetazolamide)** are acute-use agents for angle-closure glaucoma, not chronic open-angle management. - **Topical latanoprost** dosing: 1 drop in affected eye(s) once daily in evening; common side effect is iris pigmentation darkening. ## Mnemonics **GLAUCOMA DRUGS & ASTHMA: SAFE vs. DANGER** **SAFE in asthma:** Prostaglandin analogues (latanoprost, travoprost, bimatoprost), alpha-2 agonists (brimonidine), carbonic anhydrase inhibitors (acetazolamide). **DANGER in asthma:** Non-selective beta-blockers (timolol, levobunolol). Use this when a patient with asthma needs glaucoma therapy. **PGA = Prostaglandin Analogue (F2α for glaucoma)** Latanoprost, travoprost, bimatoprost all end in '-prost' and are F2α analogues. Gemeprost is E1 (obstetrics only). When you see '-prost' in ophthalmology context, think glaucoma; in obstetrics, think gemeprost (E1). ## NBE Trap NBE pairs "open-angle glaucoma" with "beta-blocker" (timolol) to trap students who know timolol is effective for glaucoma but forget the asthma contraindication. The asthma comorbidity is the discriminating feature that eliminates the most commonly used glaucoma agent. ## Clinical Pearl In Indian clinical practice, asthmatic patients presenting with newly diagnosed open-angle glaucoma are routinely started on topical latanoprost monotherapy as first-line, avoiding the systemic toxicity of beta-blockers. A patient on timolol who develops asthma symptoms should be switched immediately to a prostaglandin analogue or alpha-2 agonist to prevent bronchospasm-related morbidity. _Reference: KD Tripathi Pharmacology Ch. 11 (Drugs acting on eye); Harrison Principles of Internal Medicine Ch. 396 (Glaucoma); Robbins Pathologic Basis of Disease Ch. 29 (Eye pathology)_
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