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)_