FentanylPreanesthetic MedicationMouth MucosaAdministration, BuccalAnalgesics, OpioidAdministration, OralCitrate (si)-SynthaseEar, MiddleMucous MembraneGastric MucosaCitric AcidTaurocholic AcidIntestinal MucosaIntestinal AbsorptionGastric AcidJejunumPotassium CitrateDuodenumPermeabilityIleumAnesthetics, Intravenous