Absorption of Drugs Via Passive Diffusion and Carrier‐Mediated Pathways

This chapter focuses on intestinal absorption, and specifically on how the molecules navigate across the enterocytes. It discusses the two mechanisms that are passive diffusion and carrier-mediated pathways. Passive transcellular diffusion is considered to be the main intestinal absorption mechanism for drugs due to its very high capacity and a large surface area. Fick's first law is a quantitative description of diffusion through a given surface area. It states that the observed rate of diffusion is proportional to the concentration (chemical) gradient. Gastric emptying may be slowed by external factors such as intense exercise or food intake. Delay in gastric emptying may be beneficial or detrimental depending on the situation. Proteins involved in the carrier-mediated pathway can be classified as either channels or drug transporters. Channels are aqueous-filled pores and/or tunnels formed by the arrangement of their transmembrane domain within the lipid bilayer.