Slide 25 of 76
Notes:
- Many drugs that are administered orally are fat-soluble
- This is a desirable characteristic for oral absorption because lipophilic agents can passively diffuse through membranes of the gut, whereas drugs which are not lipophilic pass unaltered through body in the stool
- However, once lipophilic drugs are absorbed, they circulate in blood bound to plasma proteins, or are sequestered in fat; thus, they are not readily excreted by the kidney into the urine
- Therefore, in order to eliminate these agents, they are converted in the body to more water-soluble metabolites which can then be excreted by the kidney
- The majority of these conversions occur in the liver, via phase I and phase II reactions
- Phase I reactions are the most common, and involve the cytochrome P450 system
