Physiological factors-Intestine transit Physiological factors-Intestine transit The longer the residence time in the small intestine,the greater the potential for complete absorption. Rectum Once emptied from the stomach,material will move along ®Small surface area the small intestine and reach the ileocecal valve in about 3 ©Little fluid content hours. ®Poor mixing The short time in small intestine is critical to the For infants and children performance of poorly water-soluble drugs,slowly Absorption is effected by fecal material and dissolving,coated dosage forms(enteric or polymer coated). retention time and sustained-release forms. Physiological factors-Intestine transit 国生 Physiological factors Ingest drugs before a meal Components and properties of GI fluids. Avoid problems associated with gastric ©Gastric emptying emptying Intestinal transit .Reduce potential drug interactions with food ©Blood f1ow components Avoid the more viscous environment in the gut Physiological factors-Intestine transit Physiological factors-Blood flow Colon Much longer residence time As a result of rapid blood perfusion of the GIT, ®mild pH the blood at the site of absorption represents a Low enzymatic activity virtual sink for absorbed material ©Small surface area Relative viscous fluidlike environment Usually,blood flow is not an important Large colonies of bacteria consideration in drug absorption. 99 Shanghai Jiao Tong University Physiological factors-Intestine transit The longer the residence time in the small intestine, the greater the potential for complete absorption. Once emptied from the stomach, material will move along the small intestine and reach the ileocecal valve in about 3 hours. The short time in small intestine is critical to the performance of poorly water-soluble drugs, slowly dissolving, coated dosage forms (enteric or polymer coated), and sustained-release forms. Shanghai Jiao Tong University Physiological factors-Intestine transit Ingest drugs before a meal • Avoid problems associated with gastric emptying • Reduce potential drug interactions with food components • Avoid the more viscous environment in the gut Shanghai Jiao Tong University Physiological factors-Intestine transit Colon Much longer residence time mild pH Low enzymatic activity Small surface area Relative viscous fluidlike environment Large colonies of bacteria Shanghai Jiao Tong University Physiological factors-Intestine transit Rectum Small surface area Little fluid content Poor mixing For infants and children Absorption is effected by fecal material and retention time Shanghai Jiao Tong University Physiological factors Components and properties of GI fluids. Gastric emptying Intestinal transit Blood flow Shanghai Jiao Tong University Physiological factors-Blood flow As a result of rapid blood perfusion of the GIT, the blood at the site of absorption represents a virtual sink for absorbed material. Usually, blood flow is not an important consideration in drug absorption