When administered concomitantly with alcohol, loratadine has no potentiating effect as measured by psychomotor performance studies.
Increase in plasma concentrations of loratadine has been reported after concomitant use with ketoconazole, erythromycin or cimetidine in controlled clinical trials, but without clinically significant changes (including electrocardiographic).
When sympathomimetic drugs are given to patients receiving monoamine oxidase (MAO) inhibitors, hypertensive reactions, including hypertensive crisis may occur. The antihypertensive effects of methyldopa, mecamylamine, reserpine and veratrum alkaloids may be reduced by sympathomimetics. β-adrenergic blocking agents also may interact with sympathomimetics. Increased ectopic pacemaker activity can occur when pseudoephedrine sulfate is used concomitantly with digitalis. Antacids increase the rate of pseudoephedrine sulfate absorption; kaolin decreases it.
Drug/Laboratory Test Interactions: Antihistamines should be discontinued approximately 48 hrs prior to skin testing procedures since these drugs may prevent or diminish otherwise positive reactions to dermal reactivity indicators.
The in vitro addition of pseudoephedrine to sera containing the cardiac isoenzyme MB of serum creatine phosphokinase progressively inhibits the activity of the enzyme. The inhibition becomes complete over 6 hrs.