Drug Interactions between Allegra and DDAVP Rhinal Tube

GENERALLY AVOID: Coadministration with large amounts of certain fruit juices, including grapefruit, orange and apple, may decrease the oral bioavailability of fexofenadine. The proposed mechanism is inhibition of drug efflux via intestinal organic anion transporting polypeptides (e.g., P-glycoprotein), of which fexofenadine is a substrate. In a five-way crossover study with 10 healthy volunteers, 1/4-strength grapefruit juice, grapefruit juice, orange juice and apple juice (300 mL with drug administration and 150 mL every 1/2 hour for up to 3 hours, total volume 1.2 L) reduced the mean area under the plasma concentration-time curve (AUC) of a 120 mg dose of fexofenadine by 23%, 67%, 72% and 77%, respectively, compared to water. Mean peak plasma concentration (Cmax) was similarly affected. The clinical significance of these changes is unknown. However, results from studies using histamine-induced skin wheals and flares found that the size of wheal and flare was significantly larger when fexofenadine was administered with either grapefruit or orange juices compared to water.

MANAGEMENT: To maximize plasma levels and therapeutic effects, fexofenadine should be taken with water. In addition, patients should refrain from consuming large amounts of grapefruit, orange, or apple juice.

Food may decrease the rate and extent of absorption of desmopressin following oral administration. In 16 healthy, nonsmoking volunteers, administration of a single 400 mcg oral dose of desmopressin concomitantly with a standardized meal (27% fat) resulted in a 52% decrease in the peak plasma concentration (Cmax) of desmopressin and a 43% decrease in systemic exposure (AUC) compared to administration in the fasting state. The Cmax and AUC were still reduced by 46% and 41%, respectively, when desmopressin was administered 1.5 hours after eating. Both feeding regimens prolonged the time to reach peak plasma concentration (Tmax) from 1 hour to 1.5 hours. However, the pharmacodynamic effects of desmopressin were not affected as assessed by urine volume and osmolality for at least 4 hours postdose. The degree of antidiuresis was similar in the absence of food and when the drug was taken with or 1.5 hours after eating. These findings would suggest a fairly minor clinical impact of the interaction in most patients, especially since oral desmopressin is intended for administration at bedtime. Nevertheless, the possibility of food effects should be considered before increasing the dose whenever a diminution of effect is noted. A significant interaction is not expected to occur with the sublingual formulation, since absorption occurs primarily in the oral mucosa, pharynx, and esophagus.