Drug Interactions between brimonidine / dorzolamide / latanoprost / timolol ophthalmic and iobenguane I 131

GENERALLY AVOID: Coadministration with drugs that reduce catecholamine uptake or deplete catecholamine stores may interfere with iobenguane I-131 uptake into neuroendocrine tumors such as pheochromocytoma and paraganglioma that express high levels of norepinephrine transporter on their cell surfaces. Since iobenguane is similar in structure to norepinephrine and is subject to the same uptake and accumulation pathways as norepinephrine, drugs that alter norepinephrine disposition in adrenergic nerve terminals and presynaptic storage vesicles will likewise affect iobenguane. Dosimetry calculations and efficacy of iobenguane I-131 may be altered. These drugs include central nervous system stimulants (e.g., amphetamines, cocaine, methylphenidate); norepinephrine and dopamine reuptake inhibitors (e.g., phentermine); norepinephrine and serotonin reuptake inhibitors (e.g., tramadol); central monoamine depleting drugs (e.g., reserpine); nonselective beta-adrenergic blockers (e.g., labetalol); alpha agonists or alpha/beta agonists (e.g., pseudoephedrine, phenylephrine, ephedrine, phenylpropanolamine, naphazoline); monoamine oxidase inhibitors; tricyclic antidepressants; norepinephrine reuptake inhibitors (e.g., bupropion, duloxetine, mirtazapine, venlafaxine); and botanicals that may inhibit reuptake of norepinephrine, serotonin, or dopamine (e.g., ephedra, ma huang, St John's wort, yohimbine). These drugs were not permitted in clinical trials that assessed the safety and efficacy of iobenguane I-131.

MANAGEMENT: Drugs that reduce catecholamine uptake or deplete catecholamine stores should be discontinued for at least five biological half-lives before administration of either the dosimetry dose or a therapeutic dose of iobenguane I-131. Do not administer these drugs until at least 7 days after each iobenguane I-131 dose. Patients should be monitored for the occurrence of clinically significant withdrawal symptoms, especially patients with elevated levels of circulating catecholamines and their metabolites.

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.