Pharmacokinetics 3

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Questions and Answers

Which factor does NOT influence the elimination half-life of a drug?

Volume of distribution

Clearance rate

Metabolic rate

Route of administration (correct)

In order to maintain therapeutic plasma drug levels, which of the following is essential?

The trough concentration should exceed the minimally effective level. (correct)

The average concentration should remain below the minimal effective level.

The drug should have a rapid elimination rate.

The peak concentration should be at the toxic level.

What is the primary purpose of a loading dose?

To provide a consistent therapeutic effect over time.

To minimize the volume of distribution of the drug.

To rapidly achieve therapeutic plasma levels before maintenance dosing. (correct)

To prevent drug toxicity during long-term treatment.

If a drug's bioavailability is less than 100%, what can be inferred about its absorption?

Some of the administered dose is lost during first-pass metabolism. Signup and view all the answers

What is the expected time required to reach a steady state of a drug based on its half-life?

Four half-lives Signup and view all the answers

What does clearance (CL) express in pharmacokinetics?

The volume of plasma containing the total amount of drug removed per time unit Signup and view all the answers

Which statement accurately describes first-order kinetics in drug elimination?

The elimination rate is directly proportional to drug concentration Signup and view all the answers

Which of the following drugs is likely to have a very high volume of distribution?

Amiodarone with a volume of 4,620 L Signup and view all the answers

What impact does saturation of clearance mechanisms have on drug metabolism?

Constant elimination rate regardless of plasma drug concentrations Signup and view all the answers

How is steady state achieved in pharmacokinetics?

When the elimination rate and absorption rate are equal Signup and view all the answers

What is true about the half-life of drugs exhibiting zero-order kinetics?

Half-life is constant and independent of drug concentration Signup and view all the answers

Which factors can affect the half-life of a drug?

Patient's age, weight, and organ function Signup and view all the answers

Which of the following statements is most accurate regarding bioavailability?

It is the percentage of a drug that reaches systemic circulation unchanged Signup and view all the answers

What determines the plasma concentration of a drug most significantly?

The interactions of absorption, distribution, metabolism, and excretion Signup and view all the answers

What is the correct implication of a low volume of distribution (Vd)?

The drug is primarily retained within the vascular compartment. Signup and view all the answers

Which factor does NOT affect drug bioavailability (F)?

Patient's age Signup and view all the answers

What is the significance of the minimum effective concentration (MEC)?

It represents the lowest concentration needed for therapeutic effect. Signup and view all the answers

Which of the following corresponds to the concept of drug elimination half-life?

The time required for the drug concentration in plasma to reduce by half. Signup and view all the answers

What necessary dosage adjustment might be required for patients with hepatic impairment?

Consider lower doses due to altered metabolism. Signup and view all the answers

Why is it important to consider pharmacogenomic profiles in dosing regimens?

They can identify patients who may experience enhanced drug effects. Signup and view all the answers

What is the primary objective of designing a therapeutic dosing regimen?

To maintain the plasma concentration within therapeutic limits. Signup and view all the answers

Study Notes

Absorption

Determines routes of administration and optimal drug dosing.
Higher bioavailability generally means a lower required dose for effective treatment.

Distribution

Drug volume of distribution correlates with dosing; higher volume often necessitates increased dosage.

Elimination

Influences drug half-life, affecting dosing frequency to maintain therapeutic plasma levels.

Therapeutic Dosing and Frequency

Aims to keep plasma drug concentrations within a safe range.
Peak concentration should be below toxic levels; trough concentration should be above minimally effective levels.

Steady State

Achieved when drug administration and elimination rates equalize.

Loading Dose

Initial large dose to quickly reach therapeutic plasma levels.
Without it, achieving steady state takes approximately four half-lives.
Example: For lidocaine with a 3.5 mg/L steady state need and a 77 L volume of distribution, calculate the loading dose accordingly.

Maintenance Dose

Regularly administered dose required to maintain target therapeutic plasma levels.
Primarily determined by clearance rates.

Clinical Applications of Pharmacokinetics

Absorption, distribution, metabolism, and excretion (ADME) determine plasma drug concentration and effectiveness.
Multiple doses often necessary for sustained therapeutic effect.
Standard dosing derived from clinical trials; patient-specific factors may influence adjustments.

Bioavailability (F)

Fraction of drug reaching systemic circulation post-administration.
Dependent on route, chemical form, and individual factors like gastrointestinal absorption and hepatic metabolism.
Bioavailability for IV administration is 100%.

Volume of Distribution (Vd)

Describes drug distribution between plasma and tissues.
Low Vd indicates drug retention in vascular space; high Vd signifies extensive distribution into nonvascular spaces.
Examples of large Vd drugs: Amiodarone (4,620 L), Digoxin (645 L).

Elimination and Clearance

Expressed in volume/time (e.g., ml/min).
Total clearance (Cltot) is a sum of rates from various elimination pathways (renal, metabolic, others).

Kinetics

First-order kinetics: Rate of elimination is proportional to drug concentration; most drugs follow this.
Zero-order kinetics: Constant drug amount eliminated over time, independent of concentration; seen in drugs like phenytoin and ethanol.
Clearance rates can saturate at therapeutic concentrations, resulting in toxic effects; increases in plasma concentration lead to no increase in clearance for zero-order kinetics.

Half-Life

Time required for plasma drug concentration to decrease by half; not constant in zero-order kinetics.
Essential for determining dosing intervals and maintaining drug effectiveness.

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Description

This quiz covers key concepts in pharmacokinetics, including absorption, distribution, elimination, and the determination of therapeutic dosing and frequency. Understand how these factors influence drug efficacy and safety in clinical settings. Delve into the importance of achieving steady-state plasma concentrations and the calculation of loading doses.