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The impact of P-glycoprotein mediated efflux on absorption of 11 sedating and less-sedating antihistamines using Caco-2 monolayers
1. Caco-2 cells were used to compare P-gp mediated efflux and passive permeability using bidirectional transport of 11 antihistamines. An efflux ratio >2 indicated active efflux, with PSC833 and GF120918 used as functional P-gp inhibitors.
2. Antihistamines were measured directly by HPLC or LC/MS.
3. Fexofenadine had an efflux ratio of 37, yet had negligible passive permeability, even in the presence of a pH gradient (0.1 × 10¯6 cm/sec). Its precursor, terfenadine, had an efflux ratio of 2.5, while cetirizine, desloratadine and hydroxyzine were 4, 7 and 14, respectively. After incubation with P-gp inhibitors, these ratios dropped significantly. Loratadine, by contrast, had equivalent transport in both directions and passive permeability was high (24 × 10¯6 cm/sec). Dimenhydrinate was the only other sedating antihistamine to exhibit efflux, with a ratio of 10.
4. Gradient conditions of pH (6/7.4) increased efflux of terfenadine and desloratadine to over 31 and 38 fold respectively, yet this increased efflux was not associated with P-gp.
5. Altering functional P-gp in the gut is likely to influence absorption of some sedating antihistamines such as dimenhydrinate and hydroxyzine and most less-sedating antihistamines except loratadine. In addition, desloratadine exhibits pH dependent efflux which could further induce variable absorption of this antihistamine.
Publication titleXenobiotica: The Fate of Foreign Compounds in Biological Systems
Department/SchoolSchool of Pharmacy and Pharmacology
PublisherTaylor & Francis Ltd
Place of publication4 Park Square, Milton Park, Abingdon, England, Oxon, Ox14 4Rn
Rights statementCopyright 2012 Informa UK, Ltd.