The document discusses the main mechanisms of drug permeation and transport across cell membranes. There are three main mechanisms: 1) Passive diffusion, which occurs along a concentration gradient through lipid or aqueous pathways without energy expenditure. 2) Carrier-mediated transport, which uses protein carriers and may be active against gradients or facilitated. 3) Pinocytosis, which involves endocytosis of macromolecules into cells through vesicles followed by exocytosis out of cells. Understanding permeation mechanisms is important for drug absorption and targeting.