Pharmacokinetics Overview
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Questions and Answers

What is the dosing interval for amlodipine required to maintain a mean steady state plasma concentration of 25 ng/ml?

  • 24 hours
  • 16 hours
  • 1400 minutes (correct)
  • 12 hours

How is the dose of Drug X calculated to maintain a steady state plasma concentration of 10 micrograms/ml?

  • Css / (ClP x T)
  • Css x ClP x F
  • Css x T / ClP
  • Css x ClP x T / F (correct)

What is the bioavailability of Drug X if its oral bioavailability is reported as 70%?

  • 0.7 (correct)
  • 0.35
  • 70%
  • 0.5

In pharmacokinetics, what does the term 'steady state' refer to?

<p>The rate of drug absorption equals the rate of elimination. (C)</p> Signup and view all the answers

What is the purpose of calculating clearance in pharmacokinetics?

<p>To measure how quickly the drug is eliminated. (B)</p> Signup and view all the answers

What is the primary concept of steady-state concentration in drug administration?

<p>It is the concentration reached when absorption equals elimination. (C)</p> Signup and view all the answers

How does increasing the dosing frequency affect the steady-state concentration?

<p>It increases the steady-state concentration. (C)</p> Signup and view all the answers

What happens to the steady-state concentration if a loading dose is administered?

<p>The steady-state concentration is reached more rapidly. (A)</p> Signup and view all the answers

What does a larger therapeutic index indicate about a drug?

<p>It has a more favorable margin of safety. (D)</p> Signup and view all the answers

How is the therapeutic index (TI) of a drug calculated?

<p>TI = TD50 / ED50 (C)</p> Signup and view all the answers

What effect does reduced kidney function have on steady-state concentration?

<p>It decreases the drug’s overall clearance rate. (A)</p> Signup and view all the answers

Why is monitoring plasma concentration essential for drugs with a low therapeutic index?

<p>To minimize drug toxicity. (D)</p> Signup and view all the answers

Which of the following describes the effect of doubling the dose while maintaining the same dosing interval?

<p>The steady-state concentration doubles. (A)</p> Signup and view all the answers

In animal toxicology studies, how is the therapeutic index calculated?

<p>TI = LD50 / ED50 (A)</p> Signup and view all the answers

In intravenous infusion, when does steady state occur?

<p>When the infusion rate equals the elimination rate. (C)</p> Signup and view all the answers

What does AUC measure in pharmacokinetics?

<p>The total exposure of the body to the drug. (A)</p> Signup and view all the answers

What characterizes first-order kinetics in drug elimination?

<p>The rate of elimination is directly proportional to drug concentration. (A)</p> Signup and view all the answers

Which scenario indicates zero-order kinetics in drug elimination?

<p>Drug elimination happens at a constant rate irrespective of concentration. (B)</p> Signup and view all the answers

For a patient like Bruno with Stage C cardiac failure, how often should digoxin levels be measured?

<p>Only when symptoms worsen or toxicity is suspected. (A)</p> Signup and view all the answers

What outcomes does the minimum effective concentration (MEC) reflect?

<p>The lowest concentration that produces a therapeutic effect. (D)</p> Signup and view all the answers

What is the primary concern when administering a drug with a narrow therapeutic index?

<p>Minimizing the risk of adverse effects. (D)</p> Signup and view all the answers

What is the bioavailability of a drug administered via intravenous injection?

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

Which factor can cause the bioavailability of an oral drug to be less than 100%?

<p>Effects of first-pass metabolism (A)</p> Signup and view all the answers

How is absolute bioavailability (Fab) defined?

<p>The ratio of AUC of an oral route to the AUC of an intravenous route (A)</p> Signup and view all the answers

What would be the bioavailability equation for an oral dosage form?

<p>F = AUCoral/Doseoral (D)</p> Signup and view all the answers

What is relative bioavailability used to compare?

<p>Two non-intravenous routes of the same drug (D)</p> Signup and view all the answers

In the SPC example provided, what is the estimated absolute bioavailability of amlodipine after a single dose?

<p>74% (C)</p> Signup and view all the answers

Which of the following statements is true regarding the absorption of amlodipine?

<p>Amlodipine is well absorbed after oral administration. (C)</p> Signup and view all the answers

What is the peak plasma level of amlodipine after oral administration of 0.25 mg/kg?

<p>25 ng/ml (D)</p> Signup and view all the answers

What does pharmacokinetics (PK) primarily describe?

<p>The body's processing of the drug (A)</p> Signup and view all the answers

Which term defines the peak plasma concentration of a drug after administration?

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

What does minimum effective concentration (MEC) indicate?

<p>The minimal concentration needed for therapeutic effects (B)</p> Signup and view all the answers

What is the definition of the therapeutic index?

<p>The ratio between the dose causing toxicity and the dose causing therapeutic effects (C)</p> Signup and view all the answers

What does the area under the curve (AUC) in a plasma concentration-time graph represent?

<p>The total absorption of the drug into the bloodstream (A)</p> Signup and view all the answers

What is the definition of drug bioavailability?

<p>The fraction of an administered dose reaching systemic circulation (A)</p> Signup and view all the answers

What is indicated by steady-state concentration?

<p>When drug absorption and elimination rates are equal (D)</p> Signup and view all the answers

Which of the following describes the term 'clearance' in pharmacokinetics?

<p>The volume of plasma from which a substance is completely removed per unit time (B)</p> Signup and view all the answers

What is the time required to reach steady state for a drug?

<p>Approximately 5 half-lives (C)</p> Signup and view all the answers

How does the drug half-life affect the peak and trough levels at steady state?

<p>Short half-life increases both peak and trough levels (A), Long half-life increases both peak and trough levels (B)</p> Signup and view all the answers

Which statement describes a characteristic of the one-compartment model?

<p>It represents drug absorption into a single central compartment (B)</p> Signup and view all the answers

Which pharmacokinetic model generally describes the behavior of most drugs?

<p>Two-compartment model (D)</p> Signup and view all the answers

What can influence drug elimination half-life in patients?

<p>Patient-specific factors, including disease state and age (C)</p> Signup and view all the answers

Which of the following is true about multi-compartment models?

<p>They are better for drugs with complex distribution patterns (A)</p> Signup and view all the answers

Which parameter is essential for calculating appropriate dosing regimens?

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

What does T½ represent in pharmacokinetics?

<p>Half-life of a drug during elimination (C)</p> Signup and view all the answers

Which of the following is a feature of the two-compartment model?

<p>It involves central and peripheral compartments (A)</p> Signup and view all the answers

What is one limitation of the one-compartment model?

<p>It oversimplifies the distribution and clearance processes (B)</p> Signup and view all the answers

Flashcards

What is Pharmacokinetics?

Pharmacokinetics (PK) studies how the body affects drugs, including how drugs are absorbed, distributed, metabolized, and eliminated (ADME).

What is Dosing Interval?

The dosing interval is the time between drug administrations.

What is Steady State Concentration?

Steady-state concentration is the point where the rate of drug administration equals the rate of drug elimination, resulting in a stable drug concentration in the body.

What is Bioavailability?

The bioavailability of a drug is the fraction of the administered dose that reaches the systemic circulation unchanged.

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What is Clearance?

Clearance is the volume of plasma cleared of a drug per unit of time.

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Minimum Effective Concentration (MEC)

The minimum concentration of a drug required to produce a therapeutic effect.

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Minimum Toxic Concentration (MTC)

The maximum concentration of a drug that can be tolerated before toxic effects occur.

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Therapeutic Range

The range of drug concentrations where the desired therapeutic effect is achieved without causing significant toxicity.

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Therapeutic Index (TI)

A measure of drug safety, calculated as the ratio between the toxic dose and the therapeutic dose.

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TD50

The dose of a drug that causes unacceptable toxicity in 50% of the population.

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ED50

The dose of a drug that produces a therapeutic effect in 50% of the population.

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Area Under the Curve (AUC)

A measure of the overall drug exposure in the body, reflecting both the amount absorbed and the duration of exposure.

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Monitoring Drug Levels

Frequent monitoring of drug levels is crucial for drugs with narrow therapeutic indices to minimize toxicity and ensure the desired therapeutic effect.

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Bioavailability

The fraction of a drug's administered dose that reaches the systemic circulation.

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Bioavailability of IV injection

Bioavailability for an intravenous injection is always 100%.

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Bioavailability of Oral drug

Bioavailability for an oral dosage form is less than 100%. This is due to factors like incomplete absorption from the gut and first-pass metabolism.

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How to calculate Bioavailability

The calculation of bioavailability.

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Absolute Bioavailability

The bioavailability of a drug administered by one route is compared to the bioavailability of the same drug administered intravenously.

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Relative Bioavailability

The bioavailability of a drug administered by one non-IV route is compared to the bioavailability of the same drug administered by another non-IV route.

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Impact of Food on Bioavailability

This refers to how the bioavailability of a drug is affected by food intake.

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SPC and Bioavailability

Information about a drug's bioavailability is commonly found in the Summary of Product Characteristics (SPC).

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Steady-State Concentration

The concentration of a drug in the plasma reached when the rate of drug absorption equals the rate of drug elimination. This occurs with repeated or continuous dosing.

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Cmax

The highest plasma concentration of a drug achieved after a single dose.

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Cmin

The lowest plasma concentration of a drug achieved between doses.

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Rate of Elimination (Kel)

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

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Infusion Rate (K0)

The rate at which a drug is administered.

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Loading Dose

An initial larger dose of a drug given to rapidly achieve therapeutic concentrations.

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Zero-Order Kinetics

Drug elimination occurs at a constant rate, independent of drug concentration.

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First-Order Kinetics

Drug elimination rate is proportional to the drug concentration.

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Half-life (T½)

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

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Steady State

The state where the rate of drug administration equals the rate of drug elimination, resulting in a constant concentration of drug in the body.

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One-compartment Model

A simplified model that assumes the drug is distributed into a single compartment, representing all organs and tissues.

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Two-compartment Model

A more realistic model that takes into account the distribution of the drug into both a central compartment (bloodstream) and a peripheral compartment (tissues).

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Multi-compartment Model

Complex models that describe the distribution of drugs into multiple compartments, representing different organs and tissues. Used when the drug's behavior is more intricate.

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Drug Elimination

The process of drug elimination from the body, typically involving metabolism and excretion.

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Drug Absorption

The process of drug absorption into the bloodstream from the site of administration.

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Drug Distribution

The process of drug distribution throughout the body, reaching different organs and tissues.

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Pharmacokinetics (PK)

The study of how drugs move through the body, including absorption, distribution, metabolism, and excretion.

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Time to Reach Steady State

The time it takes for the drug concentration in the bloodstream to reach a steady state after repeated doses.

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Peak concentration (Cmax)

The highest concentration of a drug in the bloodstream after administration.

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Time to peak concentration (tmax)

The time it takes for a drug to reach its peak concentration in the bloodstream.

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Therapeutic index

The ratio between the dose/concentration of a drug producing toxicity and the dose/concentration that produces a therapeutic effect. A measure of drug safety.

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Drug bioavailability

The fraction of an administered dose of a drug that reaches the systemic circulation unchanged.

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Study Notes

Pharmacokinetics

  • Pharmacokinetics (PK) is the study of how the body handles a drug, including absorption, distribution, metabolism, and excretion (ADME).
  • Pharmacodynamics (PD) is the study of what the drug does to the body.
  • Peak concentration (Cmax) is the highest drug concentration in the blood after administration.
  • Time to peak concentration (tmax) is the time it takes for the drug to reach its peak concentration.
  • Area Under the Curve (AUC) is the total drug exposure.
  • The therapeutic index (TI) is the ratio between the dose that produces a toxic effect and the dose that produces a therapeutic effect.
  • The minimum effective concentration (MEC) is the minimum drug concentration required to produce a therapeutic effect.
  • The minimum toxic concentration (MTC) is the minimum drug concentration at which toxicity usually occurs.
  • Bioavailability (F) is the fraction of the administered dose that reaches the systemic circulation.
  • IV injections have 100% bioavailability.
  • Oral administration has bioavailability less than 100% due to factors such as first-pass metabolism.
  • Clearance is the rate of elimination of a drug, for many drugs it is considered constant.

Volume of Distribution

  • Volume of distribution (VD) is a theoretical volume that would be needed to contain the total administered drug dose at the observed concentration.
  • Vd is an indication of the extent of drug distribution in the body.
  • High Vd suggests extensive distribution throughout tissues.
  • Low Vd suggests a high concentration in the plasma.

Clearance

  • Drug clearance is the rate at which a drug is removed from the body.
  • It is defined as the ratio of the rate of drug elimination to the plasma concentration.
  • Clearance is often expressed in units of volume per unit time (e.g., L/h or mL/min).
  • Overall drug clearance is the sum of clearance by the liver, kidneys, and other organs.
  • High clearance rate means the drug is eliminated more efficiently.
  • Low clearance rate means the drug is eliminated less efficiently.

Zero and First Order Kinetics

  • Zero-order elimination: The rate of elimination is constant, regardless of the drug concentration.
  • First-order elimination: The rate of elimination is proportional to the drug concentration.
  • Most drugs follow first-order kinetics.

Half-life (T½)

  • Half-life (t½) is the time taken for the drug concentration to decrease by 50%.
  • Half-life is constant in first-order elimination.
  • It takes approximately 5 half-lives to reach steady state.

Steady State

  • Steady state is when the rate of drug absorption is equal to the rate of drug elimination.
  • At steady state, the drug concentration in the plasma plateaus.
  • Additional repeated doses of a drug do not change steady state levels any further.

Learning Objectives

  • Define pharmacokinetics and differentiate it from pharmacodynamics
  • Define peak concentration (Cmax), half-life (t½), time to peak concentration (tmax), AUC, therapeutic index, minimum effective concentration and minimum toxic concentration
  • Describe the concepts of steady state, volume of distribution and clearance
  • Describe and explain the differences between zero and first-order kinetics
  • Describe one, two and multi-compartment models of drug distribution and elimination
  • Explain how to calculate dosing interval

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Description

This quiz covers the key concepts of pharmacokinetics, including absorption, distribution, metabolism, and excretion of drugs. It also explores important measurements like peak concentration, therapeutic index, and bioavailability. Test your understanding of how drugs interact with the body and their effects.

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