Study Notes on Drug Metabolism and Transport

Disclaimer and Introduction to the Lecture

  • The lecture is tailored for students who have already taken previous courses in drug metabolism, particularly RX501.
  • Metabolism Transport covers core principles of drug metabolism with real-time applications.

Overview of Drug Metabolism

  • Definition of Metabolism: The process of altering molecules.
  • Importance of Drug Metabolism: Improves water solubility for better excretion from the body.
  • Key Functions: Understanding the differentiation between Phase One and Phase Two Metabolism.
    • Brief Review: Students should be familiar with drug metabolism basics, including various enzymes (e.g., cytochrome P450).

Phase One vs. Phase Two Metabolism

  • Phase One Metabolism: Typically involves the introduction of functional groups to increase water solubility. Enzymes involved: Cytochrome P450 (CYP) family.
  • Phase Two Metabolism: Involves conjugation reactions that increase molecular size and polarity, making drugs more water-soluble and ready for excretion (e.g., glucuronidation, sulfation).

Role of Specific Enzymes

  • Key Enzymes in Phase One Metabolism:
    • CYP2C9, CYP2C19, CYP2D6, CYP3A4: Critical for drug metabolism.
    • Students should understand enzyme functions and specific substrates.
  • Key Enzymes in Phase Two Metabolism:
    • SULTs, NATs, GSTs: Their roles in drug clearance will be emphasized.

Drug vs. Prodrug

  • Essential Distinction: A prodrug requires metabolism to become pharmacologically active.
  • Example: Codeine as a prodrug that converts to morphine, an active analgesic through metabolism by CYP2D6.

Impact of Metabolism Changes

  • Consequences of Metabolism Dysfunction: Understand how altered metabolism can lead to toxicity or therapeutic failure.
    • Discuss potential risks if the drug clearance mechanism fails (e.g., toxicity due to overdose).
    • Case Studies: Attendees will review specific examples and patient scenarios.

Atorvastatin Example

  • Atorvastatin: A commonly using drug for cholesterol management. Importance of CYP3A4 in atorvastatin metabolism.
  • Prescribing Implications: Risks associated with CYP3A4 inhibitors leading to altered drug clearance.

Importance of Metabolism and Clinical Application

  • Metabolism as a Key Factor:
    • Responsible for approximately 70% of drug clearance from the body.
    • Variability in patient metabolism due to genetics, age, and other factors is critical to drug prescriptions.

Saturable Metabolism

  • Concept of limited enzyme availability leading to saturation.
    • Example: Ineffective drug concentrations may lead to toxicity or insufficient therapeutic effects based on enzyme activity levels.

Genetic Variability in Drug Metabolism

  • Genetic differences affect CYP activity leading to variable drug responses in different individuals.
  • Relevant to drug interactions and personalized medicine considerations.
    • Example of Codeine: Variability in response due to gene polymorphisms in CYP2D6 affecting morphine production.

Examples of Drug Interactions

  • Increased Drug Concentrations: Discussing how drug interactions can lead to increased plasma levels (e.g., digoxin and clarithromycin interaction).
  • Decreased Efficacy: Dealing with induction of enzymes that can lower drug levels in therapeutic contexts (e.g., increased metabolism can reduce drug effectiveness).

Transporters in Drug Metabolism

  • Drug Transporters: Classifications into ABC (ATP-binding cassette) transporters and SLC (solute carrier) transporters.
    • Understanding their physiological roles in drug absorption and distribution will be discussed.

Organ-Specific Transport Functions

  • Major organs involved (liver, kidneys, brain) in transport functions and how they affect drug bioavailability.
  • Importance of understanding transporter location and activity for effective drug design.

Conclusion and Practical Application

  • Emphasizing the clinical relevance of understanding drug metabolism and transport mechanisms.
  • Encouragement to be aware of food, drug interactions, and genetic variations that can influence therapeutic success.
  • Resource suggestions: FDA tables and guidelines for drug interactions and enzyme activity.

Summary and Review Questions

  • To solidify understanding, there will be practice questions based on metabolism effects, transporter functions, and enzyme interactions.

  • Review questions will challenge knowledge of specific transporters and their implications in pharmacotherapy.

  • Closing: Push for clarity on how these metabolic and transport concepts interact with prescribing information and patient care during discussions about drugs' functions in the body.