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Questions and Answers
What is the basic principle of pharmacokinetics?
What is the basic principle of pharmacokinetics?
Which statement is true regarding the one compartment model?
Which statement is true regarding the one compartment model?
What characterizes the two compartment model of drug disposition?
What characterizes the two compartment model of drug disposition?
In first order kinetics, how does the rate of decrease in drug concentration relate to the amount of drug in the body?
In first order kinetics, how does the rate of decrease in drug concentration relate to the amount of drug in the body?
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Which of the following describes the semi-log plot for one compartment first order kinetics?
Which of the following describes the semi-log plot for one compartment first order kinetics?
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What is a key feature of first order elimination kinetics?
What is a key feature of first order elimination kinetics?
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Which phase of drug concentration decline occurs first in the two compartment model?
Which phase of drug concentration decline occurs first in the two compartment model?
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Which of the following is NOT a characteristic of pharmacokinetics?
Which of the following is NOT a characteristic of pharmacokinetics?
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What percentage of furosemide is ionized in plasma when the pH is 7.4?
What percentage of furosemide is ionized in plasma when the pH is 7.4?
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Which form of cocaine is predominant when the pH is 7.4 and pK is 8.4?
Which form of cocaine is predominant when the pH is 7.4 and pK is 8.4?
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How does the route of administration affect drug absorption?
How does the route of administration affect drug absorption?
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What is the major factor affecting the rate of drug absorption in oral administration?
What is the major factor affecting the rate of drug absorption in oral administration?
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Which statement correctly describes the Henderson-Hasselbalch equation as applied to weak acids?
Which statement correctly describes the Henderson-Hasselbalch equation as applied to weak acids?
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Which of the following statements about the partition coefficient (P.C.) is correct?
Which of the following statements about the partition coefficient (P.C.) is correct?
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What distinguishes weakly basic drugs from weakly acidic drugs in terms of proton exchange?
What distinguishes weakly basic drugs from weakly acidic drugs in terms of proton exchange?
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Which molecular property is primarily influenced by the overall polarity of the drug?
Which molecular property is primarily influenced by the overall polarity of the drug?
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In the context of the Henderson-Hasselbalch equation, what does a weak acid (HA) do in a solution?
In the context of the Henderson-Hasselbalch equation, what does a weak acid (HA) do in a solution?
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What role do functional groups play in determining the characteristics of drug molecules?
What role do functional groups play in determining the characteristics of drug molecules?
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Study Notes
Pharmacokinetics Overview
- Quantitative expression linking absorption, distribution, and elimination of drugs over time.
- Drug effects correlate with blood concentration levels.
Relationship Between Drug Concentration and Effect
- Drug efficacy is directly related to blood concentration.
- Variations in blood concentration influence the therapeutic effect of the drug.
Models of Drug Disposition
One Compartment Model
- Assumes rapid equilibration of drug between plasma and tissues, treating the body as a single compartment for elimination.
- Semi-log plot of plasma concentration versus time shows a straight line following first-order kinetics.
- Changes in plasma concentration correspond to proportional changes in tissue concentration, noting that not all tissues uniformly receive the drug.
Two Compartment Model
- Involves a delayed equilibrium between plasma and tissue, consisting of a central and peripheral compartment.
- The drug can circulate between the central compartment (primary elimination site) and the peripheral compartment.
- Semi-log plots display two distinct phases during first-order kinetics: an initial distribution phase (rapid plasma concentration decline) followed by an elimination phase.
Elimination Kinetics
First Order Kinetics
- Defined as the rate of drug concentration decrease being directly proportional to the total drug amount in the body.
- A constant fraction of the drug is eliminated over time, characteristic of most pharmaceuticals.
- The equation governing this process is ( C = (dose/Vd) e^{-kt} ), where ( ke ) is the elimination rate constant.
- The rate of elimination is consistent regardless of drug dose, emphasizing a constant fraction removed at any given time.
- Graphical representation of first-order kinetics shows a straight line in semi-log plots for one compartment models.
Physicochemical Properties of Drugs
- Molecular Size: Determined by atom number, type, and spatial arrangement (straight vs. branched chains).
- Solubility: Affected by overall polarity influenced by functional groups; measured using the Partition Coefficient.
- Partition Coefficient (P.C.): Calculated as P.C.= [Drug]fat/[Drug]water; P.C. > 1 indicates lipophilicity while P.C. < 1 indicates hydrophilicity.
Drug Acidity and Basicity
- Weakly Acidic Drugs (HA): Donate protons, leading to dissociation in solution; represented as HA + H2O ↔ H3O+ + A-.
- Weakly Basic Drugs (B:): Accept protons, transforming to BH+; represented as B: + H3O+ ↔ H2O + BH+.
- Neutral Drugs: Do not participate in proton transfer at physiological pH; can be neutral uncharged or charged.
Functional Groups in Drug Molecules
- Neutral Uncharged: Alcohols, aldehydes, amides, and ketones.
- Neutral Charged: Quaternary ammonium compounds.
- Acidic Groups: Carboxylic acids and sulfonamides.
- Basic Groups: Amines and guanidines.
Henderson-Hasselbalch Equation
- Equation: pH = pK + log([A-]/[HA]) for acids and pH = pK + log([B:]/[BH+]) for bases.
- Application: Calculate ionization of drugs based on pH and pK, informing drug absorption and distribution.
Drug Absorption
- Routes of Administration: Includes Enteral (GI tract), Parenteral (other body parts), and Topical (surface application).
- Oral Administration: Primary absorption occurs in the small intestine, affected by dissolution rate and first-pass metabolism.
- Sublingual Administration: Absorption bypasses the liver, useful for quickly dissolving drugs.
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Parenteral Administration:
- Subcutaneous: Diffusion at capillary membranes.
- Intramuscular: Larger volumes; suitable for irritating drugs.
- Intravenous: Directly into blood, leading to rapid effects but no possibility for retrieval.
Drug Distribution
- Influencing Factors: Physicochemical properties, biological barriers, protein binding, and disease states.
- Blood-Brain Barrier (BBB): Drugs cross mainly via passive diffusion; barriers exist due to tight junctions between capillary endothelial cells.
- Fetal Barrier: The placenta facilitates drug transfer, with most substances crossing into fetal circulation.
Protein Binding and Storage
- Types of Bonds: Include covalent, ionic, hydrogen, and hydrophobic bonds.
- Protein Binding Interactions: Can alter drug efficacy, especially in drugs with narrow therapeutic indices.
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Storage Tissues:
- Fat: Lipid-soluble drugs accumulate slowly.
- Bone: Drugs like tetracyclines bind calcium.
Biotransformation
- Definition: Conversion of drugs into metabolites, primarily occurs in the liver.
- Outcomes of Biotransformation: Can activate prodrugs, inactivate active drugs, or form toxic metabolites.
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Phases of Biotransformation:
- Phase I: Involves oxidation, reduction, and hydrolysis.
- Phase II: Involves conjugation/synthesis for enhanced excretion.
Rate of Biotransformation
- Factors affecting rate include enzyme activity, age, liver health, nutrition, genetics, and gender.
Drug Excretion
- Primary Routes: Renal (urine) and biliary (bile).
- Other Routes: Include sweat, saliva, breast milk, and exhalation.
- Elimination Concept: Distinct from excretion; refers to loss of pharmacological effect from the body.
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Description
This quiz explores the fundamental concepts of pharmacokinetics, focusing on the relationship between drug absorption, distribution, and elimination over time. It delves into key principles such as drug concentration effects and the one-compartment model of drug disposition.
