no interactions found...but grapefruit juice..GENERALLY AVOID: Grapefruit juice can inhibit CYP450 3A4 and may theoretically increase the plasma concentrations of fentanyl, which is primarily metabolized by the isoenzyme. According to some manufacturers, concomitant use of fentanyl with CYP450 3A4 inhibitors including grapefruit juice can increase or prolong adverse drug effects and may cause potentially fatal respiratory depression. Clinical data are limited. In a study with 12 healthy volunteers, consumption of 250 mL regular-strength grapefruit juice the night before and 100 mL double-strength grapefruit juice one hour before administration of oral transmucosal fentanyl citrate (600 or 800 mcg lozenge) did not significantly affect fentanyl pharmacokinetics, overall extent of fentanyl-induced miosis (miosis AUC), or subjective self-assessment of various clinical effects compared to control. However, pharmacokinetic alterations associated with interactions involving grapefruit juice are often subject to a high degree of interpatient variability. The possibility of significant interaction in some patients should be considered. MANAGEMENT: Although clinical data are limited, consumption of grapefruit and grapefruit juice should preferably be avoided during treatment with fentanyl. Patients and/or their caregivers should be advised to seek medical attention if potential signs and symptoms of toxicity occur such as dizziness, confusion, fainting, extreme sedation, bradycardia, slow or difficult breathing, and shortness of breath. Patients treated with transdermal formulations of fentanyl should be cautioned that drug interactions and drug effects may be observed for a prolonged period beyond removal of the patch, as significant amounts of fentanyl are absorbed from the skin for 17 hours or more after the patch is removed.