Drug Interactions between brimonidine / timolol ophthalmic and KIE

MONITOR: Beta-blockers may antagonize the cardiostimulatory effects of ephedrine by blocking beta-1 adrenergic receptors in the heart. Parenteral ephedrine may be less effective in the treatment of shock and hypotension if the patient is receiving, or has recently received, a beta-blocking drug. In addition, peripheral vascular resistance may increase due to unopposed alpha-adrenergic effect of ephedrine in the presence of beta-blockade. Theoretically, the interaction may also occur with beta-blocker ophthalmic preparations, since they may be systemically absorbed and can produce clinically significant systemic effects even at low or undetectable plasma levels.

MANAGEMENT: Clinicians should be alert to the potential for diminished cardiac response when parenteral ephedrine is used in patients treated with beta-blockers, including ophthalmic formulations.

GENERALLY AVOID: Noncardioselective beta-blockers can antagonize the bronchodilating effects of ephedrine by blocking beta-2 adrenergic receptors in smooth muscles of the bronchial tree. The interaction is less likely to occur with cardioselective beta-blockers, which generally have little effect on beta-2 adrenergic receptors at therapeutic dosages. However, cardioselectivity is not absolute and may be lost with larger doses.

MANAGEMENT: Noncardioselective beta-blockers, including ophthalmic formulations, should generally be avoided in patients using ephedrine-containing preparations for bronchospastic diseases. If beta-blocker therapy is necessary, an agent with beta-1 selectivity (e.g., atenolol, metoprolol, betaxolol) is considered safer. However, caution is advised, especially with higher dosages of the beta-blocker.

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MONITOR: Topically administered alpha-2 adrenergic receptor agonists such as apraclonidine and brimonidine are systemically absorbed, with the potential for producing rare but clinically significant systemic effects such as hypotension and bradycardia. The possibility for an additive or potentiating effect on blood pressure and heart rate should be considered when used with other medications that affect these parameters, such as ophthalmic and systemic beta blockers, vasodilators, cardiac glycosides, and antihypertensive agents.

MANAGEMENT: Blood pressure and pulse rate should be monitored regularly when topical alpha-2 adrenergic receptor agonists are prescribed in combination with cardiovascular drugs. Patients should be advised to notify their physician if they experience slow pulse, irregular heartbeat, dizziness, lightheadedness, or syncope.

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