Drug Interaction Report

MONITOR: Monoamine oxidase inhibitors (MAOIs), tricyclic antidepressants (TCAs), catechol-O-methyltransferase (COMT) inhibitors, thyroid hormone, antihistamines, cardiac glycosides (e.g. digoxin) and diuretics may potentiate the response to epinephrine, including fatal consequences, in the treatment of serious systemic reactions that may occur during immunotherapy with allergenic extracts. Vasoconstricting and hypertensive effects may be potentiated by MAOIs, tricyclic antidepressants, and COMT inhibitors. Arrhythmogenic effects may be potentiated by thyroid hormones, antihistamines, cardiac glycosides and diuretics.

MANAGEMENT: Immunotherapy with allergenic extracts may not be appropriate in patients receiving MAOIs, tricyclic antidepressants, COMT inhibitors, thyroid hormone, antihistamines and cardiac glycosides as these patients may experience an exaggerated response to the usual doses of epinephrine required to reverse a systemic reaction.

ADJUST DOSING INTERVAL: Coadministration of peanut allergen extract with alcohol may potentiate the risk of allergic reactions, including anaphylaxis. According to some studies, alcohol is an augmenting factor influencing immunological mechanisms that can induce more severe allergic reactions and is involved in up to 15% of cases of anaphylactic reactions. Proposed mechanisms include an increase in allergen absorption from altered permeability of the intestinal epithelial barrier, enhancing mast cell and basophil activation, and an increase in serum IgE concentrations. In addition, according to product labeling, administration of peanut allergen extract during a fasting state may potentiate the risk of allergic reactions, including anaphylaxis. The exact mechanism has not been elucidated.

MANAGEMENT: To minimize the risk of allergic reactions, including anaphylaxis, some authorities recommend alcohol not be consumed for 2 hours before, or 2 hours after taking peanut allergen extract. If alcohol cannot be avoided, withholding or decreasing peanut allergen dosage should be considered. Peanut allergen extract should also be administered with an evening meal and not within 2 hours of bedtime.

GENERALLY AVOID: Concurrent use of ethanol and phenothiazines may result in additive CNS depression and psychomotor impairment. Also, ethanol may precipitate dystonic reactions in patients who are taking phenothiazines. The two drugs probably act on different sites in the brain, although the exact mechanism of the interaction is not known.

MANAGEMENT: Patients should be advised to avoid alcohol during phenothiazine therapy.