Levonor should be used cautiously in patients with hyperthyroidism, hypertension and cardiac arrhythmias. All
vasopressors should be used cautiously in patients taking monoamine oxidase (MAO) inhibitors.
Levonor should not be administered concomitantly with other sympathomimetic drugs (such as isoproterenol)
because of possible additive effects and increased toxicity.
Combined effects may induce serious cardiac arrhythmias. They may be administered alternately when the preceding
effect of other such drug has subsided.
Administration of epinephrine to patients receiving cyclopropane or halogenated hydrocarbon general anesthetics
such as halothane which sensitize the myocardium, may induce cardiac arrhythmia.. When encountered, such arrhythmias
may respond to administration of a beta-adrenergic blocking drug. Levonor also should be used cautiously with
other drugs (e.g., digitalis, glycosides) that sensitize the myocardium to the actions of sympathomimetic drugs.
Diuretic agents may decrease vascular response to pressor drugs such as epinephrine.
Levonor may antagonize the neuron blockade produced by guanethidine resulting in decreased antihypertensive
effect and requiring increased dosage of the latter.