“…On the other hand, adsorption of drugs onto dietary constituents (Toothaker and Welling, 1980;Huupponen et al ., 1984;Welling, 1996;Marathe et al ., 1998;Fleisher et al ., 1999), reduced contact time with GIT, formation of diffusion barrier owing to higher viscosity in the upper small intestine (Fleisher et al ., 1999), higher degradation by gastric acid (Lentz, 2008), complex formation and/or precipitation of the drug by bile salts, heavy metal ions, and/or calcium (Neuvonen, 1976;Welling, 1977;Deppermann and Lode, 1993;Drabant et al ., 2004) could decrease their absorption. The other factors that alter drug absorption are hyper-or hypotonicity (Borowitz et al ., 1971;Ochsenfahrt and Winne, 1971;Welling, 1977), formulation (Karim et al ., 1985a,b;Waldman and Morganroth, 1995;Zhi et al ., 1995;Benziger et al ., 1996;Schug et al ., 2002), contact angle or wetting (Horter and Dressman, 2001), and modification of pH of the urine (Drabant et al ., 2004). The important physicochemical and physiological differences in fasted state and fed state GIT are summarized in Table 14.3.…”