Pharmacokinetics Overview
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Questions and Answers

What is the primary factor that reduces bioavailability after administration via non-IV routes?

  • Increased gastric emptying
  • Efficient distribution
  • Incomplete absorption (correct)
  • High lipid solubility

    • What happens to the peak concentration of a drug that is absorbed more slowly?

  • It is lower and occurs later (correct)
  • It remains unchanged
  • It occurs earlier
  • It becomes higher than expected

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

  • First-pass hepatic metabolism
  • Patient age and gender (correct)
  • Solubility of the drug
  • Nature of drug formulation

    • What is the importance of calculating the area under the curve (AUC) in pharmacokinetics?

    <p>It estimates the bioavailability of a drug</p> Signup and view all the answers

    What characteristic of a drug affects its absorption across lipid-rich cell membranes?

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

    Which statement accurately describes bioequivalence?

    <p>Two drugs must show comparable bioavailability and similar peak times</p> Signup and view all the answers

    Which formulation factor is least likely to affect a drug's dissolution and absorption rate?

    <p>Color of the tablet</p> Signup and view all the answers

    Why are drugs that are extremely hydrophobic poorly absorbed?

    <p>They cannot cross the lipid membranes due to their solubility</p> Signup and view all the answers

    What does pharmacokinetics primarily affect regarding drugs?

    <p>The absorption, distribution, and elimination of drugs</p> Signup and view all the answers

    Which factor does NOT directly influence plasma concentration of a drug?

    <p>Rate of drug synthesis</p> Signup and view all the answers

    How is the volume of distribution (Vd) calculated?

    <p>By dividing the amount of drug in the body by plasma drug concentration</p> Signup and view all the answers

    What can cause an alteration in the volume of distribution?

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

    What is the primary objective in long-term drug administration?

    <p>To maintain steady-state concentrations within a therapeutic window</p> Signup and view all the answers

    What does clearance (CL) help to determine in pharmacokinetics?

    <p>The elimination rate in relation to administration</p> Signup and view all the answers

    Which would typically NOT influence the effective drug concentration at the receptor site?

    <p>Rate of drug financing</p> Signup and view all the answers

    Which statement about the relationship between effective drug concentration and plasma concentration is incorrect?

    <p>Plasma concentration does not affect the effective drug concentration</p> Signup and view all the answers

    What is the relationship between clearance and plasma concentration for a drug eliminated by first-order kinetics?

    <p>Clearance remains constant regardless of plasma concentration.</p> Signup and view all the answers

    How is the half-life of a drug determined?

    <p>By volume of distribution and clearance.</p> Signup and view all the answers

    What happens to the half-life of a drug if clearance decreases?

    <p>Half-life increases.</p> Signup and view all the answers

    Which of the following equations describes the steady-state concentration of a drug?

    <p>Dosing rate = CL x C<del>ss</del></p> Signup and view all the answers

    Which factor does NOT affect the clearance of a drug?

    <p>Concentration of the drug administered.</p> Signup and view all the answers

    What is bioavailability?

    <p>The fraction of the administered dose that reaches systemic circulation.</p> Signup and view all the answers

    When is bioavailability considered to be 100% for a drug?

    <p>When the drug is administered intravenously.</p> Signup and view all the answers

    What does the equation CL = Rate of elimination / Plasma drug concentration indicate?

    <p>CL measures the body's ability to eliminate a drug.</p> Signup and view all the answers

    What defines two drugs as therapeutically equivalent?

    <p>They have comparable efficacy and safety.</p> Signup and view all the answers

    What is indicated by a high hepatic extraction ratio?

    <p>Low bioavailability after oral administration.</p> Signup and view all the answers

    What is the primary purpose of a dosage regimen?

    <p>To achieve therapeutic levels without surpassing toxic levels.</p> Signup and view all the answers

    How is the maintenance dosage determined?

    <p>As a function of clearance.</p> Signup and view all the answers

    When is a loading dose particularly necessary?

    <p>When the volume of distribution is large.</p> Signup and view all the answers

    What effect does renal disease have on drug elimination?

    <p>It can reduce the clearance of drugs dependent on renal function.</p> Signup and view all the answers

    Which statement regarding the relationship between therapeutic and toxic concentrations is true?

    <p>Large differences allow for larger doses at infrequent intervals.</p> Signup and view all the answers

    What condition may lead to reduced hepatic clearance?

    <p>Heart failure.</p> Signup and view all the answers

    Study Notes

    Pharmacokinetics

    • Pharmacokinetics studies how the body affects drugs.
    • It focuses on absorption, distribution, elimination, and how they influence drug concentration.

    Effective Drug Concentration

    • Concentration of drug at the receptor site determines drug effectiveness.
    • This concentration is usually proportional to the drug's concentration in plasma or blood at equilibrium.
    • It's a function of absorption, distribution, and elimination rates.

    Volume of Distribution (Vd)

    • Vd is a hypothetical volume representing how a drug spreads in the body.
    • It relates the amount of drug in the body to the concentration in the plasma.
    • Vd is affected by the drug's affinity for tissues.
    • Conditions like liver or kidney disease can influence Vd for protein-bound drugs.

    Clearance (CL)

    • CL is crucial for designing drug regimens to maintain therapeutic levels.
    • It represents the body's ability to eliminate a drug and is essential for steady-state concentration calculations.
    • Steady-state concentration is reached when the rate of elimination equals the rate of administration.
    • The relationship between dosing rate, clearance, and steady-state concentration is:

    Dosage rate = CL x Css

    Half-life (t1/2)

    • Time it takes for drug concentration to decrease by 50%.
    • Determined by Vd and CL.
    • Clearance and half-life are inversely related.
    • Changes in protein binding and disease states can modify half-life.

    Bioavailability

    • Fraction of administered dose reaching systemic circulation.
    • Affected by absorption, first-pass metabolism, and distribution.
    • IV administration has 100% bioavailability.
    • Controlled-release formulations aim for smoother plasma concentration profiles.
    • Bioavailability is calculated by comparing plasma drug levels after different routes of administration with levels achieved by IV injection.

    Factors Affecting Bioavailability

    • First-pass hepatic metabolism: Rapid liver metabolism reduces bioavailability.
    • Solubility: Drugs must have a balance of hydrophobicity and hydrophilicity for good absorption.
    • Chemical Instability: Drugs can be degraded in the gastrointestinal tract.
    • Drug Formulation: Factors like particle size and excipients influence absorption.

    Bioequivalence and Therapeutic Equivalence

    • Bioequivalence: Similar bioavailability and time to reach peak levels.
    • Therapeutic Equivalence: Similar efficacy and safety.

    Extraction

    • Extraction ratio: Fraction of drug removed by an organ during blood flow.
    • Drugs with high hepatic extraction ratio experience substantial first-pass metabolism, leading to low oral bioavailability.

    Dosage Regimens

    • Plan for drug administration aiming for therapeutic concentrations without exceeding toxicity.
    • Maintenance dose: Used to maintain steady-state concentrations over time.
    • Loading dose: Given initially to quickly achieve therapeutic levels.

    Adjusting Dosage in Disease States

    • Renal or cardiac disease can decrease drug clearance, requiring dose adjustments.
    • Hepatic clearance impairment can occur due to reduced liver blood flow.

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    Pharmacokinetics Study Notes PDF

    Description

    This quiz covers key concepts in pharmacokinetics, including drug absorption, distribution, elimination, and effective drug concentration. It also delves into important metrics such as volume of distribution and clearance, which are vital for understanding drug efficacy and safety.

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