Ophthalmic Reduction of raised intraocular pressure
Adult: Instill 1 drop into affected eye(s) bid.
Contraindications
Reactive airway disease including bronchial asthma or history of bronchial asthma, severe COPD; sinus bradycardia, sick sinus syndrome SA block, 2nd- or 3rd-degree AV block. Childn (<2 yr). Concomitant use w/ MAOIs and antidepressants (e.g. TCAs and mianserin).
Special Precautions
Patient w/ 1st-degree AV block, severe peripheral circulatory disturbance/disorders (e.g. Raynaud’s phenomenon), mild to moderate COPD, metabolic acidosis and untreated phaechromocytoma, corneal disease, depression, DM, myasthenia gravis. May mask signs and symptoms of acute hypoglycaemia. Pregnancy and lactation.
Adverse Reactions
Ocular hypersensitivity, conjunctival hyperaemia, burning sensation, stinging sensation in the eye, allergic conjunctivitis, corneal erosion, superficial punctuate keratitis, eye pruritus, conjunctival folliculosis, visual disturbance, blepharitis, epiphora; eye dryness, discharge, pain and irritation; foreign body sensation, depression, somnolence, headache, HTN, oral dryness; eyelid oedema, pruritus and erythema; asthenic conditions.
May cause transient vision blurring, visual disturbances, fatigue and/or drowsiness, if affected, do not drive or operate machinery.
Monitoring Parameters
Monitor intraocular pressure and BP.
Drug Interactions
Potential additive effect w/ systemic antihypertensives e.g. β-adrenergic blockers, Ca channel blockers. May result to mydriasis w/ epinephrine. May increase hypoglycaemic effect of antidiabetics. May potentiate hypertensive reaction to sudden clonidine withdrawal. May increase risk of hypotension w/ anaesth drugs. Potentially Fatal: May reduce therapeutic effect w/ TCAs and mianserin.
Action
Description: Brimonidine tartrate is a relatively selective α2-adrenergic agonist, it reduces aqueous humour formation and increases uveoscleral outflow. Timolol maleate blocks β1 and β2 adrenergic receptors, it reduces aqueous humour production or outflow, and BP by blocking adrenergic receptors and reducing sympathetic outflow. It blocks β1 adrenergic receptors to produce negative chronotropic and inotropic activity. Onset: Peak ocular hypotensive effects: 2 hr (brimonidine); 1-2 hr (timolol). Pharmacokinetics: Absorption: Time to peak plasma concentration: W/in 0.5-4 hr (brimonidine); approx 1-2 hr (timolol). Distribution: Timolol: Crosses the placenta and enters breast milk. Plasma protein binding: 10-60%. Metabolism: Undergoes extensive hepatic metabolism (brimonidine); partial hepatic metabolism (timolol). Excretion: Via urine (as metabolites and unchanged drug). Half-life: 2-3 hr (brimonidine); 4 hr (timolol).
Chemical Structure
Brimonidine Source: National Center for Biotechnology Information. PubChem Database. Brimonidine, CID=2435, https://pubchem.ncbi.nlm.nih.gov/compound/Brimonidine (accessed on Jan. 21, 2020)
Timolol Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 33624, Timolol. https://pubchem.ncbi.nlm.nih.gov/compound/33624. Accessed July 26, 2022.
Anon. Brimonidine and Timolol. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 04/03/2016.Buckingham R (ed). Timolol Maleate. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 04/03/2016.Combigan 0.2%/0.5% Ophthalmic Solution. U.S. FDA. https://www.fda.gov/. Accessed 04/03/2016.Combigan Solution/Drops (Allergan, Inc). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 04/03/2016.Joint Formulary Committee. Brimonidine with Timolol. British National Formulary [online]. London. BMJ Group and Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 04/03/2016.McEvoy GK, Snow EK, Miller J et al (eds). Brimonidine Tartrate (EENT). AHFS Drug Information (AHFS DI) [online]. American Society of Health-System Pharmacists (ASHP). https://www.medicinescomplete.com. Accessed 04/03/2016.McEvoy GK, Snow EK, Miller J et al (eds). Timolol maleate. AHFS Drug Information (AHFS DI) [online]. American Society of Health-System Pharmacists (ASHP). https://www.medicinescomplete.com. Accessed 04/03/2016.
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