Drug Interactions between benzocaine / phenylephrine / phenylpropanolamine and Limbitrol DS

GENERALLY AVOID: Tricyclic antidepressants (TCAs) may markedly enhance the pressor response to parenteral direct-acting sympathomimetic agents and vasoconstrictor-containing local anesthetics. Several-fold increases in the effects of norepinephrine and, to a lesser extent, epinephrine and phenylephrine were reported in healthy subjects pretreated with desipramine, imipramine, or nortriptyline. The mechanism is TCA inhibition of norepinephrine reuptake in adrenergic neurons, resulting in increased stimulation of adrenergic receptors. Clinically, hypertension, throbbing headache, tremor, palpitation, chest pain, and cardiac dysrhythmia have been reported in association with this interaction. Various TCAs have been implicated including amitriptyline, desipramine, imipramine, nortriptyline, and protriptyline. It is not known whether the interaction also occurs with mixed-acting sympathomimetic agents (e.g., dopamine, ephedrine, metaraminol).

MANAGEMENT: Parenteral administration of direct-acting sympathomimetic agents should preferably be avoided during therapy with tricyclic antidepressants except in cases of emergency (e.g., treatment of anaphylaxis). If concomitant use is necessary, initial dose and rate of administration of the sympathomimetic should be reduced, and cardiovascular status including blood pressure should be monitored closely. Although clinical data are lacking, it may be prudent to follow the same precaution with mixed-acting sympathomimetic agents.

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MONITOR: Central nervous system- and/or respiratory-depressant effects may be additively or synergistically increased in patients taking multiple drugs that cause these effects, especially in elderly or debilitated patients. Sedation and impairment of attention, judgment, thinking, and psychomotor skills may increase.

MANAGEMENT: During concomitant use of these drugs, patients should be monitored for potentially excessive or prolonged CNS and respiratory depression. Cautious dosage titration may be required, particularly at treatment initiation. Ambulatory patients should be counseled to avoid hazardous activities requiring mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.

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MONITOR: The use of tricyclic antidepressants in combination with amphetamines or sympathomimetic appetite suppressants may produce additive cardiovascular effects, increasing the risk of hypertension, cardiac arrhythmias, tachycardia, and fever. The mechanism involves additive pharmacodynamic effects resulting from increased norepinephrine release by sympathomimetic agents and inhibition of norepinephrine reuptake by tricyclic antidepressants. A pharmacokinetic interaction is also possible between tricyclic antidepressants and amphetamines, since many of these agents are metabolized by CYP450 2D6. Increased plasma levels of one or both drugs may occur during coadministration.

MANAGEMENT: Close monitoring of cardiovascular status is recommended for patients receiving this combination. Patients should be advised to promptly report symptoms such as fever, headache, or fast or irregular heartbeats.

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MONITOR: Coadministration of two or more sympathomimetic agents may increase the risk of adverse effects such as nervousness, irritability, and increased heart rate. Central nervous system (CNS) stimulants, particularly amphetamines, can potentiate the adrenergic response to vasopressors and other sympathomimetic agents. Additive increases in blood pressure and heart rate may occur due to enhanced peripheral sympathetic activity.

MANAGEMENT: Caution is advised if two or more sympathomimetic agents are coadministered. Pulse and blood pressure should be closely monitored.

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