A 55-year-old woman on brimonidine 0.2% twice daily for POAG develops itching, redness, and follicular conjunctivitis after six months of use. What is the mechanism of the IOP-lowering effect of brimonidine, and what is the most likely cause of this adverse reaction?
- A Prostaglandin analogue increasing uveoscleral outflow; conjunctival hyperaemia from prostaglandin effect
- B Beta-blocker reducing aqueous production; allergic reaction to the beta-blocker moiety
- C Alpha-2 agonist reducing aqueous production; follicular reaction is a delayed hypersensitivity to the drug or preservative ✓
- D Carbonic anhydrase inhibitor; bitter taste and fatigue from systemic absorption
Correct answer: C. Alpha-2 agonist reducing aqueous production; follicular reaction is a delayed hypersensitivity to the drug or preservative
Explanation
Brimonidine is a selective alpha-2 adrenergic agonist that lowers IOP primarily by reducing aqueous humour production and secondarily by increasing uveoscleral outflow. Follicular conjunctivitis occurs in approximately 10 to 15 percent of patients after prolonged use, attributed to delayed hypersensitivity or preservative toxicity (commonly BAK). Beta-blockers cause systemic cardiopulmonary effects, not follicular reactions. Prostaglandin analogues cause hyperaemia, not follicles.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.