Questions and Answers
What is pharmacokinetics?
What the body does to the drug.
Which route of administration avoids first-pass metabolism?
First-pass metabolism occurs before the drug reaches systemic circulation.
True
What is bioavailability?
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The four classic tissue groups in drug distribution consist of VRG, Muscle, Fat, and _______.
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What happens to lipophilic drugs after a single dose?
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Drugs bound to protein are unavailable for uptake by organs.
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What model is used to describe drug distribution in the body?
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What is the primary function of transmembrane proteins?
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Active transport requires _______ to move drugs against a concentration gradient.
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Study Notes
Pharmacokinetics
- Pharmacokinetics examines how the body influences drug behavior, specifically absorption, distribution, metabolism, and elimination.
Absorption
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Routes of Administration:
- Intravenous (IV): 100% bioavailability, bypasses first-pass metabolism.
- Intramuscular (IM): Reliable but slower absorption rate.
- Subcutaneous (SQ): Less reliable, similar to IM.
- Sublingual: Direct absorption into the systemic venous system (example: NTG, fentanyl), bypassing hepatic metabolism.
- Intrathecal/Epidural/Perineural: Specific local effects.
- Inhalational: Rapid absorption through the lungs.
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First-Pass Metabolism:
- Significant for enteral routes (oral, rectal), occurs in the liver.
- Avoided with IV, IM, and sublingual routes.
Bioavailability
- Defined as the fraction of a drug that reaches systemic circulation.
- Parenteral routes have a bioavailability of 1.0 (100%).
Distribution and Redistribution
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Four Classic Tissue Groups:
- Vessel-Rich Group (VRG): Receives 75% of cardiac output; comprised of organs like the brain and heart.
- Muscle: Accounts for 50% of body weight, receiving 19% of CO.
- Fat: Makes up 20% of body weight, receives about 6% of CO.
- Vessel-Poor Group (VP): 20% body weight, receives negligible CO.
- Lipophilic Drugs: They quickly equilibrate into CNS tissue, leading to a short duration of action initially.
- Redistribution: Causes a longer apparent duration of action with multiple doses as drugs accumulate in peripheral tissues.
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Protein Binding:
- Drugs bound to plasma proteins (like albumin) are unavailable for distribution and excretion.
- Low protein levels increase free drug availability.
Two-Compartment Model
- Central Compartment: Plasma and VRG.
- Peripheral Compartment: Tissue distribution.
- Characterized by an initial spike in serum concentration followed by rapid (α phase) and slower (β phase) declines.
Transfer/Transport of Drugs
- Cell Membrane: Consists of a lipid bilayer; small lipophilic drugs permeate easily.
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Transport Mechanisms:
- Passive Transport: Drug movement down a concentration gradient, limited by blood flow.
- Facilitated Diffusion: Uses carrier proteins but no energy; dependent on concentration gradients.
- Active Transport: Energy-requiring, can occur against concentration gradients for both drug types.
Acid-Base Equilibria
- Acids and bases exist in equilibrium involving protons (H+), with environmental pH affecting the position of equilibrium.
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Description
Test your knowledge on pharmacokinetics and clinical pharmacology as relevant to anesthesiologist assistants. This quiz covers the fundamental principles of how drugs interact with the body, including absorption and concentration variations. Perfect for students enrolled in ANES 475/476.
