Drug Interactions between mixed grass pollens allergen extract and Toprol-XL

ADJUST DOSING INTERVAL: The bioavailability of metoprolol may be enhanced by food.

MANAGEMENT: Patients may be instructed to take metoprolol at the same time each day, preferably with or immediately following meals.

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ADJUST DOSING INTERVAL: Since sublingual preparations of allergenic extracts are meant to be absorbed directly from tissues under the tongue into the blood stream, consuming food or beverage during or immediately after administration may reduce the systemic bioavailability of the medication.

MONITOR: Coadministration of allergenic extracts for allergy immunotherapy 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. A causal relationship with all allergenic extracts has not been established.

MANAGEMENT: Food or beverage should not be taken with, or for at least 5 minutes after, the administration of sublingual allergenic extracts. Patients should also avoid swallowing for about 1 minute following placement of the allergen extract under the tongue. Caution is advised if allergenic extracts for immunotherapy are used concomitantly with alcohol. Some manufacturers of peanut allergen extract recommend alcohol not be consumed for 2 hours before, or 2 hours after taking peanut allergen extract and if alcohol use cannot be avoided, that withholding or decreasing peanut allergen dosage should be considered. Individual prescribing information should be consulted for further guidance and clinical monitoring may be considered.

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ADJUST DOSING INTERVAL: Concurrent administration with calcium salts may decrease the oral bioavailability of atenolol and possibly other beta-blockers. The exact mechanism of interaction is unknown. In six healthy subjects, calcium 500 mg (as lactate, carbonate, and gluconate) reduced the mean peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of atenolol (100 mg) by 51% and 32%, respectively. The elimination half-life increased by 44%. Twelve hours after the combination, beta-blocking activity (as indicated by inhibition of exercise tachycardia) was reduced compared to that with atenolol alone. However, during a 4-week treatment in six hypertensive patients, there was no difference in blood pressure values between treatments. The investigators suggest that prolongation of the elimination half-life induced by calcium coadministration may have led to atenolol cumulation during long-term dosing, which compensated for the reduced bioavailability.

MANAGEMENT: It may help to separate the administration times of beta-blockers and calcium products by at least 2 hours. Patients should be monitored for potentially diminished beta-blocking effects following the addition of calcium therapy.

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