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Movement of drugs across cellular barriers Drugs coss cellular barriers mainly by filtration (aqueous diffusion),simple
diffusion
(lipid
diffusion
)or
carrier-mediated transport(active transport and facilitated diffusion).
The main factor that determines the rate of passive diffusional transfer across membranes is a drugâs lipid solubility.
Carrier-mediated
transport(e.g.
In
the
renal
tubule ,blood-brain barrier,gastrointestinal epithelium)is important for some drugs that are chemically related to endogenous substances.
Drug absorption,distribution and elimination Most drugs are well absorbed from the gastrointestinal tract.the rate of absorption depends on the unionized fraction of drug in solution.
Lipid soluble drugs reach all compartment,and may accumulate in fat .
The amount of a drugs that is bound to plasma protein depends on three factors:the free drug concentration,its affinity of the binding sites and the protein concentration.
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