ADME: Distribution of Drugs in the Body
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Questions and Answers

What is the primary route of excretion for most drugs?

  • Hepatobiliary system
  • Lungs
  • Milk and tears
  • Kidneys (correct)

    • The Michaelis-Menton kinetics model describes the relationship between the rate of enzyme reaction and the concentration of substrate.

    True

    What are the three main mechanisms underlying renal drug excretion?

    Glomerular filtration, active tubular secretion, and passive diffusion across tubular epithelium.

    The elimination rate constant (kel) is a measure of the rate of drug's irreversible elimination from the body per unit _________________.

    <p>time</p> Signup and view all the answers

    What is the result of passive diffusion across tubular epithelium in the renal excretion process?

    <p>Lipophilic drugs are reabsorbed into the systemic circulation</p> Signup and view all the answers

    The Michaelis-Menton constant (Km) is a measure of the maximum rate of enzymatic reaction.

    <p>False</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Vmax = maximum rate of enzymatic reaction Km = substrate concentration at which the rate of enzymatic reaction is half of the maximum rate Glomerular filtration = large molecules cannot cross glomerular membrane Active tubular secretion = carried-mediated transport that may be saturated</p> Signup and view all the answers

    What is the impact of protein binding on drug distribution?

    <p>Protein binding affects drug distribution by limiting the amount of free drug available for distribution.</p> Signup and view all the answers

    The bile contains mainly ________________ conjugates, which are eventually excreted as faecal matter.

    <p>glucuronides</p> Signup and view all the answers

    What is the clinical implication of first-pass metabolism?

    <p>Higher dosage required with oral administration</p> Signup and view all the answers

    What is the primary site of absorption in the gastrointestinal tract?

    <p>Small intestines</p> Signup and view all the answers

    Ionization affects the absorption of drugs in the gastrointestinal tract.

    <p>True</p> Signup and view all the answers

    What is the primary difference between passive and active transport?

    <p>Passive transport occurs along the concentration gradient and does not require cellular energy, while active transport occurs against the concentration gradient and requires cellular energy.</p> Signup and view all the answers

    The primary active transport process involves the direct usage of ___________________ to transport molecules.

    <p>ATP</p> Signup and view all the answers

    Match the following types of transport with their characteristics:

    <p>Passive transport = Occurs along the concentration gradient Active transport = Occurs against the concentration gradient Facilitated diffusion = Requires facilitators but no cellular energy Primary active transport = Direct usage of ATP</p> Signup and view all the answers

    What is the result of saturating a transporter?

    <p>Bottleneck in transport</p> Signup and view all the answers

    Only non-diffusable or hydrophilic drugs are transported through specialized transport mechanisms.

    <p>True</p> Signup and view all the answers

    What is the consequence of saturating a transporter clinically?

    <p>Saturating a transporter can lead to decreased efficacy or adverse effects of the drug.</p> Signup and view all the answers

    The movement of molecules from a low to high concentration is known as transport against the ___________________ gradient.

    <p>concentration</p> Signup and view all the answers

    What is the primary difference between secondary active transport and primary active transport?

    <p>Indirect usage of ATP</p> Signup and view all the answers

    What is the primary function of albumin in the blood?

    <p>To maintain colloidal osmotic pressure of blood</p> Signup and view all the answers

    The bound fraction of a drug is pharmacologically active.

    <p>False</p> Signup and view all the answers

    What is the effect of high plasma protein binding on a drug's activity?

    <p>Lower activity, distribution, metabolism, and excretion</p> Signup and view all the answers

    Drug displacement may occur during _______________ interactions.

    <p>drug-drug</p> Signup and view all the answers

    Match the following drug fractions with their characteristics:

    <p>Free fraction = Pharmacologically active, gets metabolized and excreted Bound fraction = Pharmacologically inert, does not get metabolized or excreted</p> Signup and view all the answers

    What is the primary factor that influences the distribution of a drug to the site of action?

    <p>All of the above</p> Signup and view all the answers

    Lipophilic drugs are easily distributed to all compartments of the body.

    <p>False</p> Signup and view all the answers

    What is the effect of plasma protein saturation on the free fraction of a drug?

    <p>Increased free fraction</p> Signup and view all the answers

    The circulation of a drug is the first compartment to which _______________ occurs.

    <p>distribution</p> Signup and view all the answers

    What is the primary factor that affects the binding of a drug to plasma proteins?

    <p>All of the above</p> Signup and view all the answers

    Study Notes

    ADME Scheme

    • The ADME scheme refers to the Absorption, Distribution, Metabolism, and Excretion of drugs in the body.

    Distribution

    • Distribution involves the movement of drugs from the systemic circulation to the site(s) of action.
    • The extent of distribution can be widespread, organ-specific, or localized.
    • Distribution occurs in the following major fluid compartments:
      • Plasma (circulatory fluid)
      • Interstitial fluid (fluid between cells)
      • Intracellular fluid (fluid in cells)
    • The circulatory system is the first compartment to which distribution occurs.
    • Factors affecting distribution include:
      • Patient characteristics (e.g., blood flow to area, weight, age)
      • Drug characteristics (e.g., formulation, route of administration, solubility, ionization)
      • Physiological conditions (e.g., co-morbidities, drug/food interactions)

    Transport in Circulatory System

    • Drugs are transported in the circulatory system by binding to plasma proteins or dissolving in plasma.
    • Plasma proteins involved in drug binding include:
      • Albumin
      • Lipoproteins
      • Acid glycoprotein
      • α, β, and γ-globulin
    • Albumin maintains colloidal osmotic pressure of blood, carries hydrophobic molecules, and is the most important protein involved in drug binding.
    • Plasma protein binding can be affected by:
      • Hydrophilic or lipophilic properties of the drug
      • Free and bound fractions of the drug
    • Clinical implications of plasma protein binding include:
      • Decreased free fraction and biological activity if highly bound
      • Increased free fraction and biological activity if plasma proteins are saturated or depleted
      • Drug displacement during drug interactions

    Body Fat Partitioning

    • Body fat consists of a large, non-polar compartment with a poor blood supply.
    • Only drugs with high lipophilicity accumulate easily in body fat.
    • Chronic administration of lipophilic drugs can lead to accumulation of parent compound and metabolites.

    Metabolism

    • Metabolism is the process by which drugs are broken down into smaller molecules.
    • First-pass metabolism occurs in the liver and affects the bioavailability of oral drugs.
    • Clinical implications of first-pass metabolism include:
      • Higher dosage required with oral administration
      • Inter-individual variation in enzyme systems
      • Susceptibility to drug-drug interactions

    Michaelis-Menten Kinetics

    • Michaelis-Menten kinetics is a model of enzyme kinetics that describes the rate of enzyme reaction.
    • The model relates the rate of enzyme reaction (V) to the concentration of substrate (S).
    • Parameters of the model include:
      • Vmax: maximum rate of enzymatic reaction
      • Km: Michaelis-Menten constant, which is the substrate concentration at which ½Vmax is defined
    • The model allows for the interpretation of inhibition of enzyme function, including:
      • Competitive inhibition: alters the amount of substrate needed
      • Non-competitive inhibition: alters the maximum rate that can be achieved

    Excretion

    • Excretion is the removal of drugs or metabolites from the body through excretory organs.
    • Main routes of excretion include:
      • Kidneys (as urine)
      • Hepatobiliary system (as bile and faecal matter)
      • Lungs (as volatile gases)
    • Factors affecting renal excretion include:
      • Patient characteristics (e.g., age, co-morbidities, urinary pH)
      • Drug characteristics (e.g., lipophilicity, plasma protein binding)
      • Physiological conditions (e.g., renal blood flow, urinary volume)

    Elimination Rate Constant (kel)

    • Elimination rate constant (kel) is the rate of drug elimination from the body per unit time.
    • It is a measure of the rate of drug clearance from the body.

    Pharmacokinetic Concepts

    • Absorption is affected by ionization, which affects the ability of drugs to cross membranes.
    • Passive transport involves the movement of drugs across membranes without the use of cellular energy.
    • Active transport involves the movement of drugs across membranes against a concentration gradient, using cellular energy.
    • Specialized transport mechanisms, such as facilitated diffusion and active transport, can be specific to certain molecules and can be saturated.

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    Description

    Learn about the distribution of drugs throughout the body, including the movement of drugs from systemic circulation to the site of action, distribution extent, and major fluid compartments.

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