pharmaceutics and kinetics
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Questions and Answers

What is the primary factor influencing drug distribution in the body?

  • Type of drug formulation
  • Blood flow to tissues (correct)
  • Dosage frequency
  • Drug expiration date

What does absolute bioavailability measure?

  • The rate of metabolism of a drug
  • The fraction of an administered dose that reaches systemic circulation (correct)
  • The total amount of a drug in a patient
  • The duration of action of a drug

Which of the following statements about plasma concentration is true?

  • Plasma concentration increases with larger doses regardless of administration method.
  • Plasma concentration can be affected by the method of drug delivery. (correct)
  • Plasma concentration is only relevant for oral drug administration.
  • Plasma concentration has no relation to drug distribution.

What is the formula to calculate the dose of a drug based on volume and concentration?

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

What characteristic of a drug primarily determines its ability to diffuse across cell membranes?

<p>Ionization state (C)</p> Signup and view all the answers

Which compartment has the largest volume in drug distribution?

<p>Intracellular Fluid (A)</p> Signup and view all the answers

Why is intravenous (i.v.) administration considered 100% bioavailable?

<p>It directly enters systemic circulation. (A)</p> Signup and view all the answers

What is the importance of protein binding in drug distribution?

<p>It influences the free concentration of the drug in circulation. (A)</p> Signup and view all the answers

What is the volume of distribution for a drug that is highly lipophilic and tissue-bound?

<p>High volume of distribution (D)</p> Signup and view all the answers

Which of the following metabolic processes involves splitting a molecule into simpler molecules?

<p>Cleavage (A)</p> Signup and view all the answers

What is the primary organ where drug metabolism is most likely to occur?

<p>Liver (C)</p> Signup and view all the answers

How do high concentrations of water-soluble drugs affect their volume of distribution?

<p>Decreasethe volume of distribution (C)</p> Signup and view all the answers

Which statement about drug metabolites is accurate?

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

What is the role of the kidney in the process of eliminating drugs from the body?

<p>It filters and secretes drugs and their metabolites (B)</p> Signup and view all the answers

What happens to a lipid-soluble drug during metabolism?

<p>It is converted into a more hydrophilic form (C)</p> Signup and view all the answers

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

<p>Conjugation (B)</p> Signup and view all the answers

What does the AUC represent in pharmacokinetics?

<p>Extent of drug absorption (A)</p> Signup and view all the answers

What occurs at Cmax during a single oral dose administration?

<p>Rate of absorption equals rate of elimination (A)</p> Signup and view all the answers

What is the maximum safe concentration (MSC) in pharmacology?

<p>The threshold above which toxic effects occur (B)</p> Signup and view all the answers

Which of the following factors influences bioavailability?

<p>Drug solubility in the gut (D)</p> Signup and view all the answers

What does bioequivalence assess?

<p>The same drug's dosage forms in absorption rate and extent (C)</p> Signup and view all the answers

What is indicated by a therapeutic window in pharmacology?

<p>Concentration range for desired response without toxic effects (B)</p> Signup and view all the answers

Why is a drug's elimination phase described as exponential?

<p>Elimination rate decreases over time as drug concentration falls (D)</p> Signup and view all the answers

What is the primary focus of biopharmaceutics?

<p>How the properties of the drug affect its absorption (C)</p> Signup and view all the answers

In pharmacokinetics, what does tmax represent?

<p>The time at which peak drug concentration occurs (D)</p> Signup and view all the answers

What does pharmacokinetics primarily study?

<p>The time course of drug absorption and elimination (A)</p> Signup and view all the answers

What is the relationship between absorption and elimination during the absorption phase?

<p>Absorption is greater than elimination (A)</p> Signup and view all the answers

What happens to a drug's bioavailability when it is destroyed by the liver?

<p>It decreases in systemic circulation (A)</p> Signup and view all the answers

Which factor does NOT govern the distribution of drugs in the body?

<p>Dose of the drug administered (B)</p> Signup and view all the answers

Which type of drug absorption mechanism does NOT involve a carrier?

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

What type of drugs readily move across most biological membranes?

<p>Lipid-soluble drugs (C)</p> Signup and view all the answers

Why do polar molecules have low permeability across the lipid bilayer?

<p>They have low solubility in the lipid environment. (A)</p> Signup and view all the answers

What largely influences the movement of a drug across lipid membranes?

<p>The drug's ionisation state (A)</p> Signup and view all the answers

What does the process of excretion primarily involve?

<p>Eliminating drugs from the body through urine (C)</p> Signup and view all the answers

What is true about facilitated diffusion in drug absorption?

<p>It is a saturable process. (B)</p> Signup and view all the answers

Which transport mechanism is important for the passage of larger drug molecules?

<p>Endocytosis (B)</p> Signup and view all the answers

What is the lipid bilayer primarily composed of?

<p>Phospholipids (D)</p> Signup and view all the answers

What does bioavailability measure in biopharmaceutics?

<p>The amount of drug that enters plasma from a formulation (A)</p> Signup and view all the answers

What is NOT true about passive diffusion?

<p>It requires a carrier molecule. (D)</p> Signup and view all the answers

What role does pH play in drug absorption?

<p>It affects the ionisation state, influencing membrane penetration. (C)</p> Signup and view all the answers

Which mechanism requires energy for drug transport?

<p>Active transport (D)</p> Signup and view all the answers

What is a significant consideration regarding a drug's plasma concentration?

<p>Drug binding to plasma proteins can affect availability. (C)</p> Signup and view all the answers

What does the half-life of a drug determine in pharmacokinetics?

<p>The frequency of dosing (A)</p> Signup and view all the answers

In linear kinetics, how does the elimination rate relate to drug concentration?

<p>Elimination rate is proportional to concentration (A)</p> Signup and view all the answers

Which formula describes the relationship between initial concentration and concentration over time?

<p>C = Coe^-kt (C)</p> Signup and view all the answers

What percentage of a drug is typically eliminated after 5 half-lives?

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

How does frequent dosing relate to a drug's half-life?

<p>Short half-life leads to more frequent dosing (A)</p> Signup and view all the answers

What happens to the logarithm of concentration as time increases in an elimination process?

<p>It decreases exponentially (D)</p> Signup and view all the answers

What is the outcome of the formula lnC = lnCo - kt when t equals t1/2?

<p>C = Co/2 (C)</p> Signup and view all the answers

Which of the following statements is correct regarding the CYP450 enzyme?

<p>It can produce active metabolites with similar or different properties (B)</p> Signup and view all the answers

Which characteristic of drugs A and B explains their different volumes of distribution?

<p>Water solubility and tissue binding (C)</p> Signup and view all the answers

What change in a drug's properties typically occurs during the metabolism phase?

<p>It becomes more hydrophilic (B)</p> Signup and view all the answers

Which process increases the polarity of a drug molecule during metabolism?

<p>Oxidation (D)</p> Signup and view all the answers

What primarily determines the elimination route for lipid-soluble drugs?

<p>Liver metabolism to create water-soluble metabolites (B)</p> Signup and view all the answers

Which of the following statements accurately describes a factor influencing drug metabolites?

<p>Metabolites can vary in their pharmacological activity (C)</p> Signup and view all the answers

What is the primary function of the kidneys in drug elimination?

<p>Filtering drug-conjugates from blood (C)</p> Signup and view all the answers

Which drug absorption mechanism involves the combination of a drug with other molecules?

<p>Conjugation (D)</p> Signup and view all the answers

How does high protein binding affect the volume of distribution of a drug?

<p>It decreases the volume of distribution (A)</p> Signup and view all the answers

Which factor is NOT a determinant of drug distribution in the body?

<p>Dose frequency (D)</p> Signup and view all the answers

What characteristic of passive diffusion is true?

<p>It is governed by concentration gradients. (C)</p> Signup and view all the answers

What role do lipid bilayers play in drug absorption?

<p>They restrict movement of most water-soluble molecules. (A)</p> Signup and view all the answers

Which of the following best describes pharmacodynamics?

<p>Physiological effects of drugs on biological systems. (C)</p> Signup and view all the answers

In the context of drug absorption, what is the primary barrier to most water-soluble drugs?

<p>Lipid bilayer of cell membranes (A)</p> Signup and view all the answers

How does the hydrophilic nature of phospholipids affect drug absorption?

<p>It limits the absorption of hydrophilic drugs. (D)</p> Signup and view all the answers

What defines the primary process of drug absorption in biopharmaceutics?

<p>Passive diffusion via concentration gradients. (D)</p> Signup and view all the answers

Which statement about polar molecules and cell membranes is correct?

<p>Their permeability through lipid bilayers is low. (C)</p> Signup and view all the answers

What is the primary consideration for determining the absolute bioavailability of a drug?

<p>The route of administration (A)</p> Signup and view all the answers

Which factor does NOT significantly affect the drug distribution in the body?

<p>Molecular weight of the drug (B)</p> Signup and view all the answers

In drug administration, why is the intracellular fluid volume significant?

<p>It represents the largest volume compartment for drug distribution. (A)</p> Signup and view all the answers

What mathematical relationship can be used to express the relationship between administered drug dose and plasma concentration?

<p>Dose equals volume times concentration. (D)</p> Signup and view all the answers

Which of the following best describes the significance of the 'steady state' in pharmacotherapy?

<p>It reflects a balance where the rate of drug administration equals the rate of elimination. (B)</p> Signup and view all the answers

Which statement accurately reflects a characteristic of protein binding in drug distribution?

<p>Higher protein binding may lead to extended drug half-life. (C)</p> Signup and view all the answers

Which factor is critical in determining the volume of distribution (V) for a drug?

<p>Body compartment volumes available to the drug (B)</p> Signup and view all the answers

How does intravenous (i.v.) administration influence plasma drug concentrations compared to oral administration?

<p>i.v. administration achieves higher plasma concentrations more quickly. (C)</p> Signup and view all the answers

What is the main function of carrier proteins in drug absorption?

<p>To assist in the absorption of large water-soluble compounds (D)</p> Signup and view all the answers

What factor is primarily responsible for the difficulty charged drugs have in crossing lipid membranes?

<p>The lipid:aqueous drug partition coefficient (D)</p> Signup and view all the answers

How does endocytosis contribute to drug absorption?

<p>It allows the entry of large substances into cells. (D)</p> Signup and view all the answers

What is a significant implication of bioavailability in pharmacology?

<p>It assesses the amount of drug reaching systemic circulation. (C)</p> Signup and view all the answers

Which statement best describes facilitated diffusion?

<p>It is an energy-independent process involving saturation. (C)</p> Signup and view all the answers

In what scenario is active transport essential during drug absorption?

<p>When large drug molecules need to be transported against a gradient. (B)</p> Signup and view all the answers

What consideration must be taken into account regarding plasma protein binding and drug efficacy?

<p>Only unbound drugs are available for therapeutic action. (C)</p> Signup and view all the answers

How does the concept of half-life influence the administration frequency of a drug?

<p>Short half-life drugs may require administration every four to six hours. (C)</p> Signup and view all the answers

What is the significance of the equation lnC = lnCo - kt in pharmacokinetics?

<p>It models first-order kinetics and describes concentration decay over time. (D)</p> Signup and view all the answers

What relationship does the elimination rate have with drug concentration in linear kinetics?

<p>Elimination rate is directly proportional to concentration. (C)</p> Signup and view all the answers

Which formula accurately describes the calculation of drug concentration at half-life?

<p>C = Co / 2 (B)</p> Signup and view all the answers

What percentage of a drug is typically eliminated from the body after 3 half-lives?

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

In the context of half-life, what does an exponential decay represent?

<p>Concentration decreases at a rate proportional to its current value. (A)</p> Signup and view all the answers

Which statement best defines the relationship between half-life and the time to achieve steady-state concentration?

<p>Steady-state is achieved after three half-lives for most drugs. (B)</p> Signup and view all the answers

In pharmacokinetics, what behavior does the term 'first-order kinetics' refer to?

<p>The elimination rate increases with an increase in drug concentration. (A)</p> Signup and view all the answers

What characterizes the absorption phase during a single oral dose of a drug?

<p>Drug absorption exceeds drug elimination. (C)</p> Signup and view all the answers

Which factor plays a crucial role in determining bioavailability?

<p>Solubility of the drug in the gastrointestinal tract. (B)</p> Signup and view all the answers

What does the term Cmax refer to in pharmacokinetics?

<p>The maximum concentration of a drug in the bloodstream. (D)</p> Signup and view all the answers

In a pharmacokinetic study involving a single oral dose, what occurs at tmax?

<p>Drug absorption rate equals the drug elimination rate. (D)</p> Signup and view all the answers

What does the therapeutic window signify in pharmacology?

<p>The range between minimum effective concentration and maximum safe concentration. (B)</p> Signup and view all the answers

What is the significance of the AUC in pharmacokinetics?

<p>It indicates the total drug exposure over time. (A)</p> Signup and view all the answers

What does bioequivalence specifically assess between two drug formulations?

<p>Equivalence in terms of the rates and extents of absorption. (C)</p> Signup and view all the answers

Why is the elimination phase of a drug described as exponential in nature?

<p>The drug is removed at a rate proportional to the remaining concentration. (B)</p> Signup and view all the answers

What role does MEC play in pharmacokinetics?

<p>Indicates the threshold concentration required for a therapeutic effect. (A)</p> Signup and view all the answers

Which of the following factors does NOT influence the bioavailability of a drug?

<p>Environmental temperature. (C)</p> Signup and view all the answers

Flashcards

Biopharmaceutics

The study of how a drug's physical and chemical properties, dosage form, and route of administration affect its absorption into the body.

Pharmacokinetics

The study of what happens to a drug in the body over time, including absorption, distribution, metabolism, and elimination.

Pharmacodynamics

Study of how drugs interact with the body to produce their effects.

Drug Absorption

The movement of a drug from its site of administration into the bloodstream.

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Drug Distribution

How the drug is distributed throughout the body.

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Drug Metabolism

The breakdown of a drug by the body to make it easier to eliminate.

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Drug Excretion

The process of removing the drug and its metabolites from the body.

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Passive Diffusion

The movement of a drug across a cell membrane based on differences in concentration.

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Bioavailability

A measure that combines the rate and extent of a drug's absorption into the bloodstream. It's calculated by analyzing the area under the curve (AUC) of a drug concentration versus time plot.

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Cmax

The maximum concentration of a drug in the blood plasma after a single dose. It reflects the peak of absorption.

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Tmax

The time it takes for a drug to reach its maximum concentration in the blood plasma after a single dose.

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Therapeutic Window

The minimum effective concentration (MEC) is the lowest concentration of a drug needed to achieve a desired therapeutic effect. The maximum safe concentration (MSC) is the highest concentration of a drug that can be safely tolerated without causing toxicity.

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Drug Elimination

The process by which a drug is removed from the body. This can happen through various routes, such as urine, feces, or breath.

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Bioequivalence

Two different drug formulations containing the same drug are considered bioequivalent if they provide the same rate and extent of absorption.

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Bioavailability Differences

The difference between the rate and extent of absorption of a drug in different formulations. It's represented by the difference in AUC, Cmax, and Tmax.

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Factors Influencing Bioavailability

Factors that influence the bioavailability of a drug, such as the drug's solubility, stability in the gut, metabolism by the liver, and absorption through the gut wall.

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Lipid:aqueous drug partition coefficient

A measure of how easily a drug moves between watery and oily environments. A higher coefficient means the drug moves more readily into oily environments like cell membranes.

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Ionisation state of a drug

The tendency of a drug to acquire an electrical charge, which can affect its ability to cross cell membranes. Charged drugs have a harder time crossing these oily membranes.

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Drug pKa

A property of a drug related to its tendency to become charged at a certain pH value. It helps determine how much of the drug is charged (and thus less likely to pass through membranes) at a given pH.

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Facilitated Diffusion

A process where drugs cross cell membranes with the assistance of carrier proteins. No additional energy is required.

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Active Transport

A process where drugs cross cell membranes against the concentration gradient, meaning from a lower concentration to a higher concentration, requiring energy. It often involves carrier proteins.

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Endocytosis

A process where large substances, including very large drug molecules or particles, are transported into cells by being enclosed in a vesicle.

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Exocytosis

A process where substances, including large drug molecules or particles, are transported out of cells by being enclosed in a vesicle.

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What is the 'steady state' in pharmacodynamics?

The steady state is reached when the rate of drug administration equals the rate of drug elimination. It's the point where the concentration of the drug in the body remains relatively constant over time.

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Why is protein binding important for understanding drug action?

Protein binding is the reversible attachment of a drug to proteins in the blood, primarily albumin. This affects the amount of free drug available to exert its effect on the body.

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What is 'absolute bioavailability' and how is it calculated?

Absolute bioavailability refers to the fraction of the administered drug dose that reaches the systemic circulation, It compares the amount of drug absorbed after oral administration to the amount absorbed after intravenous injection.

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What is the 'volume of distribution' about, and what does it tell us?

Volume of distribution is an apparent volume of fluid that a drug distributes in the body. It reflects how extensively a drug distributes into tissues compared to the blood.

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Where do drugs distribute in the body? Describe the factors.

Drugs can distribute into various compartments: Plasma, interstitial fluid, and intracellular fluid. This depends on both the drug's solubility (aqueous or lipid) and blood flow to different tissues.

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Half-life (t1/2)

The time it takes for the concentration of a drug in the body to decrease to half its initial value.

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Half-life and Dosing Frequency

Drugs with a short half-life need to be given more frequently to maintain therapeutic levels, while those with a long half-life can be given less frequently.

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First-Order Kinetics

Most drugs follow first-order kinetics, meaning their elimination rate is proportional to the concentration of the drug in the body. This means that the amount eliminated per unit time is constant.

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Elimination Time and Half-life

After approximately 5 half-lives, over 95% of the drug is eliminated from the body.

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Exponential Decay of Drug Concentration

The relationship between drug concentration and time can be represented by an exponential decay equation: C = Coe-kt. This equation describes how the drug concentration decreases over time.

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Calculating Half-life from Experimental Data

Plotting the natural logarithm of drug concentration (lnC) versus time will produce a straight line with a slope equal to -k. This slope allows us to calculate the elimination rate constant (k), which is essential for determining the half-life.

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What is volume of distribution (Vd)?

The volume of distribution (Vd) is the apparent volume into which a drug distributes in the body. It reflects how much of the drug stays in the blood (low Vd) or distributes into tissues (high Vd).

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Why do water-soluble drugs have a low Vd?

Highly water-soluble drugs or those bound to proteins are more likely to stay in the blood, leading to a lower volume of distribution. They are not readily distributed to tissues.

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Why do lipid-soluble drugs have a higher Vd?

Lipid-soluble drugs or those bound to tissues readily leave the bloodstream and distribute to tissues, leading to a higher volume of distribution.

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What is metabolism?

Metabolism is the chemical change that occurs to a drug in the body. It often makes the drug more water-soluble, aiding in elimination.

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Where does metabolism happen?

Metabolic processes can occur in many tissues, but the liver is the primary site. Other key sites include kidneys, lungs, and the gastrointestinal tract.

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Explain 'cleavage' in drug metabolism.

One way drugs are metabolized is by splitting into smaller molecules. For example, a large molecule could be broken into two smaller molecules.

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Describe oxidation in drug metabolism.

A major metabolic process involves adding oxygen to the drug molecule or removing hydrogen, which makes the molecule more water-soluble. This facilitates elimination.

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What is conjugation in drug metabolism?

Conjugation is the attachment of a molecule, such as glucuronic acid or sulfuric acid to a drug molecule. This makes the drug more water-soluble, helping eliminate it from the body.

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What is biopharmaceutics?

The study of how a drug's physical and chemical properties, dosage form, and route of administration affect its absorption into the body.

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What is drug absorption?

The movement of a drug from its site of administration into the bloodstream.

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What is passive diffusion?

The movement of a drug across a cell membrane based on differences in concentration. It doesn't require energy or a carrier protein.

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Why are cell membranes important for drug absorption?

Cell membranes are barriers that keep ions, proteins, and other molecules from diffusing in or out of cells and are primarily made of phospholipids, which have hydrophilic heads and hydrophobic tails.

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How do cell membranes impact polar drug absorption?

Polar molecules have low solubility in the hydrophobic core of a lipid bilayer and hence have low permeability coefficients across the bilayer.

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What is pharmacokinetics?

The study and characterization of the time course of drug absorption, distribution, metabolism, and elimination.

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What is pharmacodynamics?

The study of the biochemical and physiological effects of the drug on the body.

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What are the key processes in pharmacokinetics?

Distribution, metabolism, and excretion are the key processes in pharmacokinetics.

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Minimum Effective Concentration (MEC)

The minimum concentration of a drug required to achieve a desired therapeutic effect.

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Maximum Safe Concentration (MSC)

The maximum safe concentration of a drug, above which toxic effects can occur.

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What is the 'steady state'?

A steady state is reached when the rate of drug administration equals the rate of drug elimination. This means the drug concentration in the body remains relatively constant over time.

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What is the importance of the steady state?

The steady state is important because it represents the desired therapeutic range of the drug. Maintaining a steady state ensures that the drug concentration remains within the effective range for the desired duration.

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What is protein binding?

Protein binding is the reversible attachment of a drug to proteins in the blood, primarily albumin. This process affects how much free drug is available to exert its therapeutic effect.

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Why is protein binding important?

Protein binding is important because it determines the free drug concentration in the body. Only unbound drugs can interact with their targets and exert their therapeutic effect, while bound drugs are inactive.

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What is absolute bioavailability?

Absolute bioavailability is the fraction of the administered drug dose that reaches the systemic circulation, comparing oral to intravenous administration. This allows for standardized evaluation of drug absorption across different routes and formulations.

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Where do drugs distribute in the body?

Drugs can distribute into various compartments: Plasma, interstitial fluid, and intracellular fluid. This depends on both the drug's solubility (aqueous or lipid) and blood flow to different tissues.

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Why do lipid-soluble drugs have a higher Vd than water-soluble drugs?

Lipid-soluble drugs tend to have a higher volume of distribution because they can readily pass through cell membranes and distribute into tissues. Water-soluble drugs often stay within the bloodstream with a lower Vd.

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Drug Elimination Rate Constant (k)

The rate of drug elimination from the body is constant. The amount eliminated per unit time is equal to a fraction of the drug concentration.

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Volume of Distribution (Vd)

The apparent volume into which a drug distributes in the body. It reflects how much of the drug stays in the blood (low Vd) or distributes into tissues (high Vd).

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Lipid-soluble Drugs and Cell Membranes

Drugs can pass through cell membranes more easily if they are lipid-soluble. They can readily pass through cell membrane lipids.

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Study Notes

Introduction to Biopharmaceutics

  • Biopharmaceutics is the study of the relationships between a drug's physical and chemical properties, its dosage forms, and the resulting biological effects after administration.
  • Pharmacokinetics studies the quantitative aspects of drug absorption, distribution, metabolism, and excretion (ADME).

Biopharmaceutics and ADME

  • Biopharmaceutics explores how a drug's properties and dosage form affects its absorption, distribution, metabolism, and excretion.
  • Pharmacokinetics quantifies the time course of these processes.

Absorption

  • Absorption is the movement of a drug from the site of administration into the bloodstream.
  • Passive diffusion occurs across membranes via a concentration gradient, without a carrier and low structural specificity.
  • Cell membranes are primarily lipid bilayers (also in sub-cellular structures), acting as barriers for most water-soluble compounds.
  • Polar or water-soluble drugs need channels or carrier-mediated processes (e.g., facilitated, active transport) due to low permeability in lipid bilayers.
  • Active transport requires energy to move drugs against concentration gradients, and facilitated diffusion uses carrier proteins.
  • Endocytosis and exocytosis facilitate uptake of large molecules.

Bioavailability

  • Bioavailability measures the amount of drug reaching the systemic circulation after administration.
  • It's calculated by comparing the area under the curve (AUC) of a drug's plasma concentration-time profile for oral administration versus intravenous administration.
  • Factors affecting bioavailability include drug destruction in the gut, poor absorption, and metabolism by gut wall or liver before reaching systemic circulation.
  • Intravenous administration has 100% bioavailability.

Single Oral Dose

  • A graph shows the blood plasma concentration versus time post oral drug intake, showing an absorption and elimination phase.
  • The initial rise represents drug absorption, peaking at Cmax at the maximum absorption rate, and then eliminating exponentially, governed by first-order kinetics.
  • Blood levels must remain in the therapeutic window (MEC to MSC) to maintain treatment efficacy. Minimum effective concentration (MEC) is the minimum effective drug concentration required for efficacy. Maximum safe concentration (MSC) is the concentration beyond which toxic effects occur.

Factors Influencing Bioavailability

  • Several factors impact the rate and extent of absorption. These factors can affect the amount of drug reaching systemic circulation, including gut destruction, poor solubility, and liver or gut wall destruction.

Bioequivalence

  • Bioequivalence refers to dosage forms of the same drug showing similar rates and extents of absorption, usually with 80-120% variation. The similarity is based on bioavailability considerations.

Regular Drug Dosing and Steady State

  • Regular drug administration aims to maintain steady state plasma concentrations. This graphical representation shows the predictable pattern of fluctuating plasma drug concentrations after consistent dosing intervals.

Protein Binding

  • The binding of drugs to plasma proteins influences their distribution and elimination.
  • Often the unbound/free form of a drug is the active form, directly interacting with its target, while a bound fraction is pharmacologically inactive.
  • Bound drugs have limited ability to penetrate tissues or organs, and are thus less likely to have a pharmacological effect.

Oral vs Intravenous Administration

  • Intravenous administration delivers the drug straight into the blood, resulting in a rapid and predictable concentration profile, contrasted with oral administration which needs to pass through various biological barriers and potentially metabolize. Intravenous administration has 100% bioavailability. A graph from slide 19 of 33 illustrated this difference.

Drug Distribution

  • Drugs distribute into body compartments such as plasma, interstitial fluid, and intracellular fluid, based on factors like drug solubility and blood flow. The presentation also discusses the volumes contained in these.

Volume of Distribution

  • Volume of distribution (Vd) describes the theoretical volume needed to contain the total amount of drug in the body at the measured concentration.
  • Vd can be high for lipid-soluble drugs or drugs bound to tissues and low for drugs predominantly present in plasma. Plasma volume is about 3 liters.

Metabolism

  • Metabolism, also called biotransformation, alters a drug chemically in the body.
  • It may convert a lipophilic drug to a more hydrophilic form for easier excretion.
  • Metabolites may be inactive or active and are products of drug metabolism. Several pathways for metabolism are outlined including cleavage, oxidation, conjugation and reduction.

Elimination

  • Major elimination routes are the liver (metabolism and secretion), kidneys (filtration and secretion), lungs (exhalation), and less significant through other routes, such as in mother’s milk, sweat, or saliva.
  • Kidney excretion frequently involves glomerular filtration and further metabolism by the liver.
  • Elimination rate is frequently determined by the half-life of the drug. T1/2 is the time taken to reduce the drug concentration in the body by 50%, with multiple half-life intervals ultimately leading to drug elimination.
  • The rate of elimination is exponential and is commonly graphed as the natural logarithm of concentration vs. time.

Half-life

  • Drugs with short half-lives need more frequent dosing, while drugs with longer half-lives can be administered less frequently.
  • Exponential decay describes how the drug concentration declines over time. Half-life calculation uses a plot of the natural log of drug concentration versus time to determine the elimination rate constant (k). Calculations show examples of how half-lives are used to determine dosing frequencies.

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Introduction to Biopharmaceutics PDF PHA114 2024

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Test your knowledge on the key concepts of drug distribution in the body. This quiz covers topics such as bioavailability, plasma concentration, and the role of various organs in drug metabolism. Challenge yourself with questions designed for pharmacology students.

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