Food and bile micelle binding of zwitterionic antihistamine drugs

Abstract

Background and purpose: The food effects on oral drug absorption are challenging to predict from in vitro data. Food intake has been reported to reduce the oral absorption of several zwitterionic antihistamine drugs. However, the mechanism for this negative food effect has not been clear. The purpose of the present study was to evaluate the bile micelle and food binding of zwitterionic antihistamine drugs as a possible mechanism for the negative food effects on their oral drug absorption. Experimental approach: Bilastine (BIL), cetirizine (CET), fexofenadine (FEX), and olopatadine (OLO) were employed as model drugs. The fed/fasted AUC ratios of BIL, CET, FEX, and OLO after oral administration are reported to be 0.60 to 0.7, 0.92, 0.76 to 0.85, and 0.84, respectively. The unbound fraction (fu) of these drugs in the fasted and fed state simulated intestinal fluids (FaSSIF and FeSSIF, containing 3 and 15 mM taurocholic acid, respectively) with or without FDA breakfast homogenate (BFH) was measured by dynamic dialysis. Key results: The FeSSIF/ FaSSIF fu ratios were 0.90 (BIL), 0.46 (CET), 0.76 (FEX), and 0.78 (OLO). In the presence of BFH, the fu ratios were reduced to 0.52 (BIL), 0.22 (CET), 0.39 (FEX), and 0.44 (OLO). Conclusion: Despite being zwitterion at pH 6.5, the antihistamine drugs were bound to bile micelles. Bile micelle and food binding were suggested to cause a negative food effect on the oral absorption of these drugs. However, the AUC ratio was not quantitatively predicted by using FeSSIF + BFH.