Pharmacokinetics Chapter 5 Quiz
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Questions and Answers

What does the first-order absorption model imply about the rate of drug absorption?

  • The rate of absorption is constant over time.
  • The rate of absorption decreases with time. (correct)
  • The rate of absorption increases exponentially.
  • The absorption occurs at a fixed rate unit.

Which parameter is NOT typically calculated after oral administration using pharmacokinetic modeling?

  • Volume of distribution (Vd)
  • Hepatic clearance (CLh) (correct)
  • Bioavailability (F)
  • Absorption rate constant (Ka)

What condition might lead to a flip-flop of absorption and elimination rate constants?

  • Constant plasma concentration.
  • Zero-order elimination.
  • Rapid elimination compared to slow absorption. (correct)
  • High bioavailability.

Which parameter most directly relates to the time taken to reach the maximum plasma concentration (Tmax)?

<p>Absorption rate constant (Ka) (D)</p> Signup and view all the answers

What assumption is made about bioavailability when applying the one-compartment oral absorption model?

<p>It is considered to be complete (F=1). (C)</p> Signup and view all the answers

Which statement accurately describes the relationship between Ka and Cmax/Tmax for dosage forms?

<p>Ka increases if Cmax increases and Tmax decreases. (B)</p> Signup and view all the answers

What outcome is true when comparing bioavailability (F) for different dosage forms?

<p>F increases if AUC increases. (D)</p> Signup and view all the answers

Which comparison of absorption rate constants (Ka) is valid given that Tmax is the same for both formulations?

<p>Ka for tablets (X) and capsules (Y) are equal. (B)</p> Signup and view all the answers

Which statement correctly identifies the limitations on the profiles after IV bolus administration?

<p>Z is impossible if AUC of X and Y are lower than P. (D)</p> Signup and view all the answers

When determining the relationship of the dosage forms in terms of their pharmacokinetic parameters, which option is incorrect?

<p>If the AUC for a dosage form is lower, its bioavailability is higher. (D)</p> Signup and view all the answers

What does the variable Cmax represent in absorption calculations?

<p>The maximum plasma concentration after an oral dose (B)</p> Signup and view all the answers

Which parameter is independent of the dose in determining tmax?

<p>Ka, the first absorption rate constant (A), K, the first-order elimination rate constant (D)</p> Signup and view all the answers

Under what assumption does the equation Cp = A e^{-Kt} simplify?

<p>Ka is much greater than K (D)</p> Signup and view all the answers

How is the net change in concentration at Cmax characterized?

<p>It becomes zero as absorption equals elimination (B)</p> Signup and view all the answers

What is the effect of increasing the fraction of the dose absorbed (F) on Cmax?

<p>C<del>max</del> increases proportionally (A)</p> Signup and view all the answers

What is the significance of the time constant in the equation for tmax?

<p>It reflects the relationship between absorption and elimination rates (B)</p> Signup and view all the answers

In the context of the equations provided, what is the role of V?

<p>It represents the total volume for drug distribution (B)</p> Signup and view all the answers

What must the relationship between Ka and K be for the assumptions outlined to hold true?

<p>Ka must be greater than K (C)</p> Signup and view all the answers

What does AUC represent in pharmacokinetics?

<p>The measurement of the extent of bioavailability (D)</p> Signup and view all the answers

Which formula is used to calculate AUC for a one-compartment IV administration?

<p>AUC = Intercept(A) × (1/K - 1/Ka) (A)</p> Signup and view all the answers

Which statement describes the relationship between Ka and K in certain circumstances?

<p>Ka can be greater than K initially after IV administration (D)</p> Signup and view all the answers

If the half-life, t ½, is known to be 10, what is the value of K?

<p>0.0693 (D)</p> Signup and view all the answers

How does AUC behave under linear conditions with constant clearance (CL)?

<p>AUC is directly proportional to dose (D)</p> Signup and view all the answers

What is the correct expression for Cmax?

<p>Cmax = D0 × Ka/V × e^{-Ktmax} (C)</p> Signup and view all the answers

For two-compartment extravascular administration, what is the expression for AUC?

<p>AUC = FD0/CL (D)</p> Signup and view all the answers

When calculating AUC using the formula involving the intercept, what does the slope represent?

<p>The elimination rate constant (C)</p> Signup and view all the answers

What happens to Cmax when the Ka value decreases?

<p>C<del>max</del> decreases (B)</p> Signup and view all the answers

Which statement is true regarding the effects of increasing the dose?

<p>AUC remains unchanged (C)</p> Signup and view all the answers

In the context of linear pharmacokinetics, what is one characteristic of IV administration?

<p>The clearance rate remains constant across doses (A)</p> Signup and view all the answers

What is true about the absorption process after reaching Tmax?

<p>It slows down but does not stop (C)</p> Signup and view all the answers

What is the relationship between Ka, dose, and Cmax?

<p>C<del>max</del> is a function of both Ka and dose (B)</p> Signup and view all the answers

If a drug has a Ka value of 0.231 and K value of 0.0693, what can be inferred?

<p>The drug's absorption rate is higher than its elimination rate (D)</p> Signup and view all the answers

What would happen to the absorption half-life if the dose is increased without changing the formulation?

<p>It would remain unchanged (B)</p> Signup and view all the answers

What is expected from plotting the differences of drug plasma concentrations at corresponding time points?

<p>A straight line with a slope of <em>--K<del>a</del>/2.3</em> (A)</p> Signup and view all the answers

What does Cp stand for in the context of the table of plasma concentrations?

<p>Concentration of plasma at any time (D)</p> Signup and view all the answers

Which equation describes the relationship between the concentration at steady state and the initial concentration when examining drug elimination?

<p>Cp = A*e^(-Kt) (B)</p> Signup and view all the answers

What was the drug dosage administered in the example provided?

<p>100 mg (C)</p> Signup and view all the answers

During which time point did the highest plasma concentration occur in the provided example?

<p>8 hours (B)</p> Signup and view all the answers

What is the value of A at the y-intercept after extrapolating the elimination phase line?

<p>70 (C)</p> Signup and view all the answers

What does the negative exponential function in the drug plasma concentration imply?

<p>Rapid elimination of the drug from the body (A)</p> Signup and view all the answers

Which time points had plasma concentration values which can be represented as A*e^(-Kt)?

<p>2 hr and 4 hr (A)</p> Signup and view all the answers

To accurately plot the data provided, which type of graph paper should be used?

<p>Semi-logarithmic graph paper (C)</p> Signup and view all the answers

In the example provided, what was the plasma concentration at 36 hours?

<p>5.88 mcg/mL (B)</p> Signup and view all the answers

What is the significance of taking the y-intercept in the context of elimination phase line extrapolation?

<p>It represents the starting concentration before drug elimination (A)</p> Signup and view all the answers

Which time interval recorded the plasma concentration of 9.95 mcg/mL in the example?

<p>1 hour (A)</p> Signup and view all the answers

What is the primary purpose of plotting the drug concentrations in this study?

<p>To assess the drug's half-life in the body (C)</p> Signup and view all the answers

Flashcards

Oral drug absorption

The process of a drug moving from the gastrointestinal tract into the bloodstream after oral administration.

One-compartment model

A simplified model representing drug absorption and distribution where the entire body is treated as a single compartment.

Absorption rate constant (Ka)

The rate at which a drug is absorbed from the site of administration into the bloodstream.

Elimination rate constant (Ke)

The rate at which a drug is eliminated from the body.

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Plasma concentration-time profile

A graph showing the concentration of a drug in the plasma over time following administration.

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Oral drug absorption equation

The equation that describes the plasma concentration of a drug over time after oral administration, considering both absorption and elimination.

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Cmax: Maximum plasma concentration

The highest concentration of a drug reached in the plasma after oral administration.

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Tmax: Time to reach maximum concentration

The time it takes for a drug to reach its highest concentration in the plasma after oral administration.

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Method of residuals: Ka calculation

A technique for determining the absorption rate constant (Ka) from oral absorption data by analyzing the terminal phase of the plasma concentration-time profile.

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Assumptions of Method of residuals?

The method of residuals for Ka calculation assumes that the absorption rate constant (Ka) is much larger than the elimination rate constant (K) and that drug absorption is complete.

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Why use the method of residuals?

The method of residuals allows us to determine the absorption rate constant (Ka) from oral absorption data, even when direct measurement is not possible.

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Ka and Tmax Relationship

As the absorption rate constant (Ka) decreases, the time to reach maximum concentration (Tmax) increases.

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Ka and Cmax Relationship

As the absorption rate constant (Ka) decreases, the maximum concentration (Cmax) decreases.

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Dose and Cmax Relationship

Increasing the dose proportionally increases the maximum concentration (Cmax).

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Dose and Tmax Relationship

Changing the dose does not affect the time to reach maximum concentration (Tmax).

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Linear Pharmacokinetics in IV Dosing

The elimination parameters (K, Cl, Vd) remain constant regardless of the dosage administered intravenously.

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Linear Pharmacokinetics in Oral Dosing

Both disposition and absorption parameters remain constant across different doses for a given formulation. However, different formulations may have different absorption parameters.

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AUC in Linear Pharmacokinetics

The area under the concentration-time curve (AUC) is proportional to the dose.

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What is CL/F?

CL/F is the "apparent" clearance of a drug, which accounts for both elimination and absorption.

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AUC: Area Under the Curve

The total amount of drug that enters the bloodstream over time, calculated by measuring the area under the plasma concentration-time curve. It reflects the total drug exposure.

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CL: Clearance

The volume of plasma that is cleared of drug per unit of time. It reflects how efficiently the body removes the drug from circulation.

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Ka: Absorption Rate Constant

The rate at which a drug is absorbed from the gastrointestinal tract into the bloodstream. A higher Ka means faster absorption.

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AUC

Area Under the Curve (AUC) represents the total amount of drug that reaches systemic circulation. It reflects the extent of drug bioavailability.

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AUC for IV Administration

For a drug administered intravenously (IV), AUC is calculated as the ratio of the initial concentration (C0) to the elimination rate constant (K).

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AUC for Extravascular Administration

For extravascular administration (like oral or intramuscular), AUC is calculated as the ratio of the dose (D0) to the clearance (CL).

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AUC and Bioavailability

AUC is a measure of the extent of drug availability in the body. A higher AUC means higher bioavailability, meaning more drug reaches systemic circulation.

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Flip-Flop of Ka and K

In some cases, the absorption rate constant (Ka) can be greater than the elimination rate constant (K). This creates a 'flip-flop' effect where the drug is absorbed faster than it is eliminated.

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Cmax

Cmax refers to the maximum concentration of a drug reached in the plasma after administration. It represents the peak level of the drug in the body.

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How is Cmax determined?

Cmax is determined by multiple factors, including the dose (D0), the volume of distribution (V), the elimination rate constant (K), and the absorption rate constant (Ka).

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AUC and Dose

Under linear conditions, AUC is directly proportional to the dose. This means doubling the dose will double the AUC.

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Plasma Concentration

The amount of a drug present in the blood plasma at a specific time.

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Time (hr)

The elapsed time after drug administration, typically measured in hours.

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Cp (mcg/mL)

Drug concentration in plasma, measured in micrograms per milliliter (mcg/mL).

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Semi-log paper

A graph paper designed for plotting data where one axis uses a logarithmic scale, typically used for visualizing exponential decay.

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Extrapolation

Estimating values beyond the measured data points by extending a trend beyond the observed data range.

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Y-intercept

The point on the y-axis where a line crosses, representing the value when the x-value is zero.

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Elimination Phase

The period where drug concentration in the blood is decreasing over time due to elimination processes like metabolism and excretion.

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Ka/2.3

The slope of the elimination phase line plotted on semi-log paper, representing the rate of drug elimination.

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Ae^-Kt

An exponential decay equation describing drug concentration over time, where 'A' is the initial concentration, 'K' is the elimination rate constant, and 't' is time.

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Why is the slope of the line -Ka/2.3 in the elimination phase?

The slope of the elimination phase line on semi-log paper represents the rate of drug elimination, which is directly proportional to the elimination rate constant (Ka). The factor of 2.3 accounts for the logarithmic scale used in plotting the concentration data on semi-log paper.

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What does the extrapolated y-intercept represent?

The extrapolated y-intercept represents the theoretical initial concentration of the drug in the plasma, assuming no drug was lost during absorption and distribution.

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How does the drug concentration decrease over time?

Drug concentration decreases exponentially over time during the elimination phase. This means the rate of decrease is proportional to the remaining concentration. As more drug is eliminated, the elimination rate slows down.

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Why is it important to know the elimination rate constant (Ka)?

The elimination rate constant (Ka) helps predict how long it takes for a drug to be eliminated from the body and consequently, determine the appropriate dosing regimen.

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What does plotting the data on semi-log paper reveal?

Plotting the data on semi-log paper allows us to visualize the exponential decay of drug concentration over time as a straight line, making it easier to determine the elimination rate constant (Ka) and the y-intercept (A) representing the initial concentration.

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Study Notes

Learning Objectives

  • Describe plasma concentration versus time profiles after oral drug administration
  • Discuss oral drug absorption following a one-compartment model
  • Calculate pharmacokinetic parameters after single oral doses
  • Describe conditions leading to changes in absorption and elimination rate constants
  • Discuss how absorption and elimination rate constants influence maximum plasma concentration and time to reach max concentration
  • Use residual method to estimate absorption rate constant, elimination rate constant, Tmax, Vd, AUC, and CL, and bioavailability

Introduction

  • Oral, intramuscular, or subcutaneous drug administration produces an additional phase in plasma concentration compared to intravenous administration
  • First-order absorption is typically considered

Drug Absorption and Distribution

  • Figure illustrating drug absorption and distribution, using terms like dose, first-order absorption rate constant, first-order elimination rate constant, plasma concentration, and volume of distribution
  • Assumptions: One-compartment system, first-order absorption, first-order elimination, and complete bioavailability

Plasma-Level Time Curve

  • Figure illustrating the plasma-level time curve after a single oral and intravenous (IV) dose
  • The model applies to solutions, rapidly dissolving forms, suppositories, and injectables (not IV)
  • Terminal phases after oral and IV administration show similar patterns

Equation for Absorption

  • Equation for the absorption process
  • Variables include dose, absorption rate constant, volume of distribution, etc.

Calculation of Maximum Plasma Concentration (Cmax) and Time to Maximum Concentration (Tmax)

  • Calculation of Cmax and Tmax is necessary due to potential issues with timing of blood samples
  • Cmax is directly proportional to dose and the fraction of absorbed dose
  • Tmax is independent of dose and depends on absorption and elimination rate constants
  • At Tmax, absorption and elimination rates are equal, resulting in zero net change in concentration

Determination of Absorption Rate Constants

  • Method of residuals to determine absorption rate constants. Assumptions: complete drug absorption and Ka >> K
  • Plotting drug concentration versus time on semi-log paper to extrapolate the terminal phase
  • Calculating differences in concentration values and plotting them against corresponding times to determine the elimination rate constant

Example 1 (Drug Plasma Concentrations)

  • Data table showcasing drug plasma concentrations over time
  • Calculation of and plotting values as exponential equations

Flip-Flop of Absorption and Elimination Rate Constants

  • Describes situations where Ka << K (the reverse of the previous examples)
  • Illustrates how Ka and K (absorption and elimination rate constants) can "flip-flop", significantly affecting drug action

Pharmacokinetic Parameters

  • Discusses how to use peak time (Tmax) to determine comparative bioavailability and bioequivalence, and to determine preferred route of administration

Peak Plasma Concentration (Cmax)

  • Used to determine bioavailability between drug products containing pharmaceutical equivalents
  • May correlate with drug pharmacological effects
  • Calculation using specific formulas involving dose, absorption and elimination constants, and the time at peak concentration

Area Under the Curve (AUC)

  • Discusses AUC in terms of bioavailability
  • AUC is the total amount of drug reaching the systemic circulation
  • AUC is directly proportional to dose
  • AUC is independent of route after drug reaches systemic circulation

Half-Life

Formula to calculate half life of elimination and absorption, relationships with clearance and Vd

Complications (Lag Time and Bioavailability)

  • Discusses lag time in drug absorption, a delay before absorption commences
  • Explains bioavailability, where absorbed drug is less than 100%. This is accounted for by use of the absorption correction factor

Linear Pharmacokinetics

  • Discusses conditions under which disposition and absorption parameters are unaffected by dose changes

Examples (Specific Drug Data)

  • Presents example problems illustrating how to use equations to calculate pharmacokinetic parameters given specific drug data

Example Problems and Calculations

  • Demonstrates how to estimate absorption rate constants K, and Ka, Vd/F and CL/F, theoretical maximum plasma concentration and time (Cmax, Tmax), AUC

Additional Considerations and Examples (Various Scenarios)

  • Shows additional details, such as scenarios for bioavailability, how to adjust for dosage amounts, or variations on rate constants and their effects

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Pharmacokinetics Of Oral Absorption PDF

Description

Test your understanding of pharmacokinetics with this quiz focused on drug absorption and distribution. Learn to distinguish between plasma concentration profiles, and calculate important pharmacokinetic parameters after oral drug administration. The quiz covers concepts essential for valuing bioavailability and the factors influencing drug concentration.

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