Brimonidine
Brimonidine
Generic Name
Brimonidine
Brand Names
* Mirapex, Detrol® (often combined with timolol).
Mechanism
Brimonidine is a selective α₂‑adrenergic receptor agonist.
• Binding: Stimulates pre‑ and post‑synaptic α₂‑receptors in ocular tissues.
• Effects:
• ↓ Intraocular pressure (IOP) by reducing aqueous humor production through decreased cAMP in ciliary epithelium.
• ↑ Outflow via enhancement of uveoscleral and trabecular meshwork drainage.
• Peripheral vasoconstriction reduces conjunctival hyperemia (common feature of glaucoma meds).
Pharmacokinetics
| Parameter | Typical Findings (Topical 0.025 % solution) |
| Absorption | Rapid penetration through cornea; peak concentration in aqueous within 5 min. |
| Distribution | Predominantly ocular; minimal systemic absorption (<0.1 %). |
| Metabolism | Minimal first‑pass effect; metabolites largely inactive. |
| Elimination | Negligible systemic elimination; ocular clearance via tear turnover and aqueous humor drainage. |
| Half‑life | Ocular: ~2–3 h; systemic: ~3.5 h (when absorbed). |
| Caution | Renal/hepatic impairment rarely affects ocular exposure. |
Indications
- Primary open‑angle glaucoma (POAG)
- Primary angle‑closure glaucoma (PACG)
- Ocular hypertension
- Post‑glaucoma surgery ocular hypotension (adjunctive therapy)
*Brand names:* Mirapex, Detrol® (often combined with timolol).
Contraindications
- Hypersensitivity to brimonidine or any excipient.
- Pediatric glaucoma: not approved for patients <12 yrs without additional evidence.
- Eg. – Quinidine‑related bradycardia when concurrent use with sympathomimetics is discouraged.
- Pregnancy: Category B – avoid if possible; no evidence of teratogenicity, but limited data.
- Cardiac arrhythmias: Use cautiously due to sympatholytic effects.
Warnings:
• Avoid systemic β‑blockers and cholinergics concurrently; may blunt IOP reduction.
• Monitor for secondary use in dry eye (off‑label); be aware of ocular surface irritation.
Dosing
| Form | Dose | Frequency | Route | Notes |
| 0.025 % eye drop | 1–2 drops per eye | 2–4 times daily | Topical | Use after cleaning eyelids. |
| 0.1 % solution (Timolol + Brimonidine combo) | 1–2 drops per eye | 2 times daily | Topical | First dose should not be taken at night if using timolol alone. |
| 0.15 % solution (Selectivity higher) | 1–2 drops per eye | Once daily | Topical | Preferred by some clinicians for ease of use. |
Formulation Tips
• Store in cool, dark environment.
• Shake well before administration.
• Avoid intraocular pressure spikes by not over‑dosing.
Adverse Effects
Common (≤10 %)
• Conjunctival hyperemia (down‑regulated by vasoconstriction; may paradoxically occur with long‑term use).
• Eye irritation / burning sensation.
• Eyelid edema.
• Dry eye symptoms.
Serious (≤1 %)
• Systemic bradycardia, hypotension.
• Allergic conjunctivitis.
• Sympathetic‑mediated changes: rescue of athletes motor performance; so not recommended for ocular use in doping contexts.
• Rare cases of ocular surface toxicity (epithelium damage with extended use).
Monitoring
- IOP: Baseline and 2–4 weeks post‑initiation.
- Visual acuity: Every visit (especially within first 2 months).
- Ocular surface status: Tear film assessment for dryness and corneal staining.
- Heart rate/Blood pressure: Check for systemic absorption signs, particularly in patients with β‑blocker use.
Clinical Pearls
- Time‑of‑day dosing: Brimonidine peaks in IOP reduction at 2–4 h; consider evening dose for better nighttime control.
- Combining with timolol improves efficacy but can mask timolol‑induced mydriasis; monitor pupil size.
- Drug–drug interactions: Avoid simultaneous use of cholinergic antagonists; synergy may worsen ocular dryness.
- Dry eye: A subset (~10 %) may inadvertently benefit from brimonidine’s slight tear film stabilization.
- Long‑term use (>6 mo): Hyperemia may shift from vasoconstrictive to vasodilative response due to receptor desensitization.
- Patient education: Instruct patients not to rinse at night after using timolol alone to avoid rebound IOP rise.
- Mini‑dose (0.025 %) may reduce side effects while maintaining IOP control; adjust based on response.
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• *This drug card provides a concise yet comprehensive overview for medical students and clinicians. For detailed prescribing information, consult the official package insert or local therapeutic guidelines.*