Pharmacology and Therapeutics
This domain tests drug selection, mechanism, contraindications, and monitoring. Items commonly ask which agent is inappropriate for a given patient rather than which is most effective.
Glaucoma agents
- Prostaglandin analogues increase uveoscleral outflow; adverse effects include iris darkening, eyelash growth, and periorbital fat atrophy.
- Topical beta blockers reduce aqueous production but can cause bronchospasm and bradycardia; avoid in reactive airway disease and caution in heart block.
- Alpha agonists such as brimonidine cause follicular conjunctivitis and fatigue; carbonic anhydrase inhibitors require attention to sulfonamide allergy and blood dyscrasias.
- Rho kinase inhibitors cause conjunctival hyperaemia and corneal verticillata.
Diagnostic and anti-inflammatory drugs
Tropicamide produces mydriasis in about 20 to 30 minutes; cyclopentolate and atropine provide cycloplegia for refraction. Phenylephrine 2.5 percent is preferred over 10 percent for routine mydriasis. Topical corticosteroids are effective but carry risks of pressure rise, cataract, and infection; never treat an undiagnosed red eye with a steroid.
Preservatives and adherence
Benzalkonium chloride can worsen ocular surface disease with frequent dosing; unpreserved preparations are preferred for severe dry eye or frequent instillation. Ask about pregnancy, breastfeeding, and other eye drops before prescribing.
Worked example
A 70-year-old with moderate persistent asthma and open-angle glaucoma needs a first-line agent. Reasoning: beta blockade can precipitate bronchospasm, so timolol is a poor choice. A prostaglandin analogue offers strong efficacy with no respiratory risk; document the rationale and review tolerance.
Traps that cost marks
Prescribing a steroid for a red eye without a diagnosis; missing a sulfa allergy; assuming all red eyes are bacterial and prescribing antibiotics; ignoring preservative load.