biopharmaceutics
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Questions and Answers

What does the lipid:aqueous drug partition coefficient indicate?

  • The ease of a drug's movement between aqueous and lipid environments (correct)
  • The percentage of a drug bound to plasma proteins
  • The concentration of a drug in systemic circulation
  • The ionization state of a drug

    • What primarily determines the ionization state of a drug?

  • The pH and the drug's pKa (correct)
  • The drug's molecular weight
  • The size of the drug particles
  • The type of drug formulation used

    • Which type of transport requires energy to move drugs across membranes?

  • Facilitated diffusion
  • Passive diffusion
  • Endocytosis
  • Active transport (correct)

    • What role do carrier proteins play in drug transport?

    <p>They are involved in the active transport of drugs</p> Signup and view all the answers

    How do water-soluble drugs typically penetrate cell membranes?

    <p>Through aqueous channels</p> Signup and view all the answers

    What does bioavailability measure?

    <p>The amount of drug that reaches systemic circulation from a formulation</p> Signup and view all the answers

    Which process allows for the entry of very large substances into cells?

    <p>Endocytosis and exocytosis</p> Signup and view all the answers

    What is the significance of a drug's half-life (t1/2) in pharmacotherapy?

    <p>It influences the frequency of drug dosing.</p> Signup and view all the answers

    What factor can complicate the therapeutic response to a drug?

    <p>Binding of the drug to plasma proteins</p> Signup and view all the answers

    How much of a drug is eliminated after three half-lives?

    <p>87.5%</p> Signup and view all the answers

    What is represented by the formula C = Coe-kt?

    <p>The exponential decay of drug concentration.</p> Signup and view all the answers

    In first order kinetics, how does the elimination rate relate to concentration?

    <p>It is directly proportional to concentration.</p> Signup and view all the answers

    What is the approximate percentage of drug eliminated after five half-lives?

    <p>95%</p> Signup and view all the answers

    Which of the following statements about active metabolites is correct?

    <p>They can have similar or different properties compared to the parent molecule.</p> Signup and view all the answers

    What happens to the drug concentration over time if the elimination rate is described by the equation kt = lnCo - lnC?

    <p>Concentration decreases exponentially over time.</p> Signup and view all the answers

    When is a drug typically administered more frequently?

    <p>When it has a short half-life.</p> Signup and view all the answers

    What is the primary factor influencing the volume of distribution (V) of a drug?

    <p>The drug's lipid solubility and blood flow</p> Signup and view all the answers

    What does absolute bioavailability measure?

    <p>The proportion of drug reaching systemic circulation relative to the administered dose</p> Signup and view all the answers

    When comparing oral and intravenous drug administration, which statement is typically true?

    <p>Intravenous administration provides immediate plasma concentration.</p> Signup and view all the answers

    Which of the following compartments can drugs distribute into?

    <p>Plasma, interstitial fluid, and intracellular fluid</p> Signup and view all the answers

    Which factor primarily affects the ability of a drug to diffuse across membranes?

    <p>The ionization state of the drug</p> Signup and view all the answers

    What is the formula used to relate the dose, volume, and concentration of a drug?

    <p>Dose = Volume x Concentration</p> Signup and view all the answers

    Why does blood flow influence drug distribution in the body?

    <p>Areas with higher blood flow receive more drug.</p> Signup and view all the answers

    What does the term 'steady state' in drug dosing refer to?

    <p>The concentration of the drug remains constant over time</p> Signup and view all the answers

    What is the maximum safe concentration (MSC) associated with?

    <p>Concentration above which toxic effects occur</p> Signup and view all the answers

    What does Cmax represent in the context of drug absorption?

    <p>The maximum concentration of a drug in plasma</p> Signup and view all the answers

    Which phase occurs when drug absorption exceeds drug elimination?

    <p>Absorption phase</p> Signup and view all the answers

    What indicates the duration of therapeutic effects without toxicity?

    <p>Therapeutic window</p> Signup and view all the answers

    Which factor is NOT related to bioavailability?

    <p>Rate of systemic circulation</p> Signup and view all the answers

    How is bioequivalence determined?

    <p>Using AUC, Cmax, and tmax</p> Signup and view all the answers

    What is the significance of tmax in drug pharmacokinetics?

    <p>Marks peak plasma concentration time</p> Signup and view all the answers

    What happens during the elimination phase of drug pharmacokinetics?

    <p>Drug elimination exceeds absorption</p> Signup and view all the answers

    What is the range of limits for considering two dosage forms bioequivalent?

    <p>80 - 120%</p> Signup and view all the answers

    What describes the effect on drug absorption when a drug is destroyed in the gut?

    <p>It decreases bioavailability</p> Signup and view all the answers

    What is the primary focus of biopharmaceutics?

    <p>Impact of the drug's physiochemical properties on absorption</p> Signup and view all the answers

    Which aspect of pharmacokinetics is studied in relation to drug elimination?

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

    What factors govern the distribution of drugs in the body?

    <p>Aqueous or lipid solubility and binding to proteins</p> Signup and view all the answers

    Which method primarily allows for drug absorption through cell membranes?

    <p>Passive diffusion</p> Signup and view all the answers

    What characteristic of the lipid bilayer affects the permeability of polar molecules?

    <p>Hydrophobic core</p> Signup and view all the answers

    Which statement correctly describes passive diffusion?

    <p>It occurs along a concentration gradient without a carrier.</p> Signup and view all the answers

    What role does the liver play in drug metabolism?

    <p>It alters drugs to more polar forms to aid elimination.</p> Signup and view all the answers

    Which statement best defines pharmacodynamics?

    <p>The examination of how drugs interact with biological systems.</p> Signup and view all the answers

    What does a high volume of distribution (V) indicate about a drug?

    <p>It is largely lipid soluble or tissue-bound.</p> Signup and view all the answers

    What is the primary organ for drug metabolism?

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

    Which metabolic process involves the splitting of a molecule into smaller parts?

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

    What characterizes the metabolism of most drugs in the body?

    <p>It typically changes from more lipophilic to more hydrophilic forms.</p> Signup and view all the answers

    What type of drug would most likely have a low volume of distribution?

    <p>Highly protein-bound drugs with low lipid solubility</p> Signup and view all the answers

    Which of the following is NOT a common route of elimination for drugs?

    <p>Directly through hair follicles</p> Signup and view all the answers

    Which metabolic process involves the combination of a molecule with glucuronic or sulfuric acid?

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

    Which statement about drug metabolites is true?

    <p>Metabolites can be either active or inactive.</p> Signup and view all the answers

    Study Notes

    Introduction to Biopharmaceutics

    • Biopharmaceutics is the study of the relationship between a drug's physical and chemical properties, dosage form, and the resulting biological effects after administration.
    • It's a qualitative study.
    • Pharmacokinetics studies the kinetics (quantitative) of drug absorption, distribution, metabolism, and excretion (ADME).

    Biopharmaceutics and Pharmacokinetics

    • Biopharmaceutics is a qualitative study of the relationship between a drug's physical and chemical properties and its dosage form, while Pharmacokinetics is a quantitative study of drug absorption, distribution, metabolism, and excretion (ADME).
    • ADME is a crucial concept in drug development, and its understanding is critical for designing effective and safe medications.

    Absorption

    • Passive diffusion involves movement across a membrane due to a concentration gradient without carrier proteins. It's nonsaturable and depends on the drug's structure.
    • Cell membranes consist of a lipid bilayer, a barrier for ions and most water-soluble molecules.
    • Absorption of lipid-soluble drugs is facile, but the diffusion rate of polar, charged molecules is limited due to their poor solubility in lipids.
    • Absorption via channels is a method for water-soluble molecules.
    • Facilitated diffusion involves a carrier protein and is saturable, while active transport requires energy to move substances against their concentration gradient.
    • Endocytosis and exocytosis are methods for absorbing large substances.
    • The pH and pKa of the drug influence absorption.

    Absorption - How?

    • A lipid-aqueous partition coefficient reflects the ease of a drug moving between water and lipid environments.
    • Drugs in ionized form have poor movement across lipid membranes.
    • The Henderson-Hasselbalch equation determines ionization state, affecting drug transport.
    • Water-soluble drugs penetrate cell membranes through aqueous channels.

    Absorption - How? (Facilitated, Active, Endocytosis/Exocytosis)

    • Facilitated diffusion utilizes carrier proteins (saturable and not requiring energy). Active transport goes against a concentration gradient and necessitates energy, often using carrier proteins.
    • Endocytosis/exocytosis deals with very large substances.

    Bioavailability

    • Therapeutic response relies on adequate drug concentration at the site of action.
    • Plasma concentration of a drug is a measure of bioavailability, representing the amount of the drug from a formulation entering the systemic circulation.
    • Bioavailability is calculated using the area under the plasma drug concentration-time curve (AUC).
    • IV administration has 100% bioavailability; non-IV bioavailability ranges from 0 to 100%.

    Single Oral Dose

    • Drug absorption is initially greater than elimination, leading to a rising plasma concentration.
    • The peak plasma concentration (Cmax) signifies the maximum drug concentration reached.
    • The time to reach Cmax (tmax) provides rate information.
    • Elimination is exponential after absorption peaks, and gradually returns to zero.
    • Minimum effective concentration (MEC) is the minimum concentration required for a desired pharmacological effect.
    • Maximum safe concentration (MSC) is above which toxic effects occur.
    • Therapeutic window is the desired response with no toxic effects.

    Factors influencing bioavailability

    • In the gastrointestinal tract, factors like drug destruction in the gut, insolubility, destruction by the gut wall, and destruction by the liver may reduce the bioavailability of a drug.

    Bioequivalence

    • Bioequivalence refers to whether two dosage forms of the same drug have similar rates and extents of absorption, with acceptable 80-120% limits.
    • Bioavailability is frequently considered to assess bioequivalence.

    Regular Drug Dosing and Steady State

    • Regular drug dosing aims to maintain a therapeutic range of drug concentration in the body.
    • A steady state is reached when the rate of drug intake equals the rate of elimination.
    • Accumulation is present immediately after first dosage administration.

    The Steady State

    • Steady state occurs when the drug intake rate is equal to the elimination rate.
    • The body's accumulated drug concentration stabilizes at this point.
    • Repeated dosings will result in concentration oscillations that eventually approach a constant plateau over time

    Importance of Protein Binding

    • Protein binding affects drug distribution, metabolism, and excretion, and influencing drug interactions.
    • Bound drugs are pharmacologically inactive.
    • Unbound drugs exert effects on the effector cells.

    Oral vs Intravenous Administration

    • Intravenous administration results in immediate high plasma drug concentrations, while oral administration takes time to reach significant plasma concentrations.

    Drug distribution

    • Drugs distribute into body compartments (plasma, interstitial fluid, intracellular fluid).
    • Distribution is influenced by factors like drug lipid solubility and blood flow to tissues.

    Volume of Distribution (Vd)

    • Volume of distribution describes the apparent volume that would be required to contain the entire dose of a drug at the same concentration as that observed in the blood plasma.
    • It’s not a physical volume; it's a theoretical space representing how a drug distributes across body compartments.
    • Vd is high for drugs largely distributed in tissues and low for drugs primarily confined to the plasma.

    Metabolism

    • Metabolism, also known as biotransformation, is the process where a drug's chemical structure is altered within the body to often more water-soluble products.
    • Metabolism often occurs in stages from lipophilic to increasingly hydrophilic forms.
    • Drugs can have multiple metabolites, some inactive, some active.
    • Metabolic processes mainly take place in the liver, kidneys, lungs, and GI tract. Cleavage, oxidation, conjugation, and reduction are examples of metabolic processes.

    Elimination

    • Elimination is the removal of drugs from the body either as the original drug or as metabolites.
    • Major organs for elimination include kidneys (filtration and secretion), liver (metabolism and secretion), and lungs (exhalation). Minor routes include sweat and saliva.

    Half-life (t1/2)

    • Half-life (t1/2) is the time taken for the plasma concentration of a drug to decrease by half after administration.
    • t1/2 significantly impacts the dosing frequency.
    • Drugs with short half-lives require more frequent dosing to maintain a therapeutic concentration.

    Half-life Calculation

    • Exponential decay formula (C = Co * e-kt) is applied to describe drug removal.
    • Taking natural logs allows the use of linear relationships to determine half-life (0.693/k).

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