Slide 24 of 76
Notes:
After oral administration, drugs pass from the intestinal tract into the liver via the portal circulation, and then enter the systemic circulation. Metabolized drugs are mainly eliminated from the body through chemical modification in the liver. The goal of metabolism is to de-toxify drugs, and make them either more water soluble (for excretion in the urine) or more fat soluble (for excretion in the bile, and then into the feces). Drug metabolism can occur in two ways:
a) Phase I Reactions: Cytochrome P450 enzymes chemically oxidize or reduce drugs.
b) Phase II Reactions: Conjugation enzymes link one chemical to another. For example, glucuronyl transferases link a glucuronide group to zidovudine, which makes it more water soluble and allows elimination in the urine.
Flexner C, Piscitelli SC. Managing Drug-Drug Interactions in HIV Disease Medscape, March 8, 2000. http://hiv.medscape.com/Medscape/HIV/ClinicalMgmt/CM.drug/public/toc-CM.drug.html
