Pharmacology for anesthesia i
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Pharmacology for Anesthesia I. Introduction. What is a Drug?. Pharmacokinetics (PK). What the body does to the drug Absorption Distribution Metabolism Excretion. Absorption. The process of diffusion or transport of a drug from the site of administration to the plasma.

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Pharmacology for Anesthesia I

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Pharmacology for Anesthesia I

Introduction


What is a Drug?


Pharmacokinetics (PK)

What the body does to the drug

  • Absorption

  • Distribution

  • Metabolism

  • Excretion


Absorption

The process of diffusion or transport of a drug from the site of administration to the plasma

Skipped by administering drugs parenterally

Inhaled agents require special considerations


Fick’s Law

concentration gradient x surface area x diffusion coefficient

membrane thickness

Rate of Diffusion =

Permeability

Size

Diffusion coefficient =


Ionization State

Henderson – Hasselbalch Equation

concentration (protonated)

concentration (unprotonated)

log

= pKa - pH


Trapping


Distribution

The process of diffusion of a drug throughout the body

Generally governed by the same characteristics as absorption

Vd = volume of distribution

Protein Binding


Metabolism

  • The enzymatic modification of the drug molecule by the body

    • Often occurs in liver

    • May occur elsewhere


Hepatic Metabolism


Example of Phase II prior to Phase I


CYP Enzymes


Pharmacogenetics of Drug Metabolism


Examples of Drug-Drug Interactions


Elimination

  • The removal of the drug from the body

    • Renal

    • Hepatic

    • Respiratory

    • Cutaneous


Clearance

  • Used to describe our ability to eliminate the active ingredient

    • Combination of metabolism and excretion

      Example of Zero order kinetics


Distribution and Clearance

  • First Order Kinetics

    • Single compartment model

    • Double compartment model

    • Three compartment model

    • Etc.


Absorption and Clearance


Effect Not Always Governed by Plasma Concentration


Dosing Regimens


Can speed accumulation time by administering a loading dose


Routes of Administration


Pharmacodynamics

  • What the drug does to the body

    • Typically receptor mediated


  • What factors affect the ability of a drug to interact with a receptor?

  • Drug size

    • Large enough to be specific

    • Not so large as to be unable to interact with the receptor

  • Drug Shape


  • Some drugs do not appear to fit into these categories

    • Osmotic agents

    • Transport regulators


Agonists

Antagonists

Competitive

Noncompetitive

Allosteric Activators

Potentiators


Partial agonists

Inverse agonists


Antagonists


Noncompetitive Antagonist and Spare Receptors


Full and Partial Agonists


Cellular Receptors


Different Drugs Similar Effects

Potency vs. Efficacy


Population Variation and Therapeutic Window


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