Updated: 8/19/2016

Phase I vs. Phase II Metabolism

Topic
Review Topic
0
0
Overview
  • Phase I metabolism 
    • oxidation (via cytochrome P450), reduction, and hydrolysis reactions
    • phase I reactions convert a parent drug to more polar (water soluble) active metabolites by unmasking or inserting a polar functional group (-OH, -SH, -NH2)
    • geriatric patients have decreased phase I metabolism
      • drugs metabolized via phase I reactions have longer half-lives
      • geriatric patients metabolism drugs by phase II reactions
  • Phase II metabolism
    • glucuronidation, acetylation, and sulfation reactions
      • "conjugation reactions" that increase water solubility of drug with a polar moiety
        • glucuronate, acetate, and sulfate, respectively
      • phase II reactions convert a parent drug to more polar (water soluble) inactive metabolites by conjugation of subgroups to -OH, -SH, -NH2 functional groups on drug
        • drugs metabolized via phase II reactions are renally excreted
      • patients deficient in acetylation capacity (slow acetylators) may have prolonged or toxic responses to normal doses of certain drugs because of decreased rates of metabolism 
 

Please rate topic.

Average 4.1 of 7 Ratings

Thank you for rating! Please vote below and help us build the most advanced adaptive learning platform in medicine

The complexity of this topic is appropriate for?
How important is this topic for board examinations?
How important is this topic for clinical practice?
Topic COMMENTS (2)
Private Note