Drug Interactions between Allegra and Onyda XR

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.

MONITOR: Many psychotherapeutic and CNS-active agents (e.g., anxiolytics, sedatives, hypnotics, antidepressants, antipsychotics, opioids, alcohol, muscle relaxants) exhibit hypotensive effects, especially during initiation of therapy and dose escalation. Coadministration with antihypertensives and other hypotensive agents, in particular vasodilators and alpha-blockers, may result in additive effects on blood pressure and orthostasis.

MANAGEMENT: Caution and close monitoring for development of hypotension is advised during coadministration of these agents. Some authorities recommend avoiding alcohol in patients receiving vasodilating antihypertensive drugs. Patients should be advised to avoid rising abruptly from a sitting or recumbent position and to notify their physician if they experience dizziness, lightheadedness, syncope, orthostasis, or tachycardia. Patients should also avoid driving or operating hazardous machinery until they know how the medications affect them.