Metabolism and Excretion in Pharmacology
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What effect does phenobarbital have on levetiracetam concentrations in dogs?

  • Increases levetiracetam concentrations significantly.
  • Decreases levetiracetam concentrations significantly. (correct)
  • Has no effect on levetiracetam concentrations.
  • Makes levetiracetam ineffective as an analgesic.

What pharmacokinetic change occurs in levetiracetam when administered with phenobarbital?

  • The clearance (Cl/F) decreases.
  • The clearance (Cl/F) increases. (correct)
  • The volume of distribution remains constant.
  • The area under the curve (AUC) increases.

What is the AUC of levetiracetam when given alone?

  • 125 µg·hr/mL
  • 88 µg·hr/mL
  • 253 µg·hr/mL
  • 184 µg·hr/mL (correct)

Which of the following best explains the interaction between levetiracetam and phenobarbital?

<p>Phenobarbital induces oxidative enzymes that accelerate levetiracetam elimination. (B)</p> Signup and view all the answers

After how many days of phenobarbital administration is the interaction observed in dogs?

<p>21 days (C)</p> Signup and view all the answers

What is the primary reason that orally administered drugs undergo hepatic metabolism before reaching systemic circulation?

<p>They pass through the hepatic portal vein, which leads to liver processing. (D)</p> Signup and view all the answers

How does the hepatic first pass effect influence the pharmacokinetics (PK) of oral lidocaine compared to intravenous administration?

<p>Intravenous administration bypasses metabolism, maintaining higher plasma concentrations. (B)</p> Signup and view all the answers

What effect does the construction of a portacaval shunt have on the pharmacokinetics of orally administered drugs?

<p>It reduces the hepatic first pass effect for those drugs. (B)</p> Signup and view all the answers

In which scenario is the first pass effect most likely to alter drug levels in circulation?

<p>When a drug is administered orally. (D)</p> Signup and view all the answers

What happens to the systemic concentration of a drug administered orally if it undergoes significant hepatic first pass metabolism?

<p>The concentration decreases due to metabolism. (D)</p> Signup and view all the answers

What is the definition of terminal elimination half-life (t1/2)?

<p>Time taken for the blood concentration of a drug to decrease by 50%. (D)</p> Signup and view all the answers

How is the terminal elimination half-life (t1/2) related to the rate constant of elimination (kel)?

<p>It is inversely proportional to kel. (D)</p> Signup and view all the answers

What does a bigger half-life imply about the elimination process?

<p>The drug takes longer to eliminate from the blood. (B)</p> Signup and view all the answers

In the context of first-order kinetics, what happens during each t1/2 interval depicted in the concentration-time curve?

<p>Half of the initial concentration is removed from the blood. (A)</p> Signup and view all the answers

Which statement accurately describes the shape of the terminal elimination phase graph for most drugs?

<p>It follows first-order kinetics. (D)</p> Signup and view all the answers

What does the ln 2 term in the equation for t1/2 represent?

<p>The natural logarithm of 2, related to exponential decay. (D)</p> Signup and view all the answers

What characteristic does a logarithmic y-axis provide in the context of the concentration-time curve?

<p>It provides a clearer representation of exponential decay. (D)</p> Signup and view all the answers

Which of the following is true regarding the effects of a higher kel on t1/2?

<p>A higher kel corresponds to a shorter t1/2. (B)</p> Signup and view all the answers

What is the primary function of the liver in drug metabolism?

<p>To enzymatically transform drugs (A)</p> Signup and view all the answers

What is a significant difference in the pharmacokinetics of meloxicam between horses and donkeys?

<p>Horses have a greater volume of distribution than donkeys (B)</p> Signup and view all the answers

What characterizes Phase 1 reactions in drug metabolism?

<p>They increase a drug's polarity and water solubility (C)</p> Signup and view all the answers

In pharmacokinetics, what does a steeper slope in a concentration versus time graph indicate?

<p>A shorter half-life (B)</p> Signup and view all the answers

What happens to the drug’s distribution as a result of biotransformation?

<p>It is confined primarily to the extracellular space (B)</p> Signup and view all the answers

What distinguishes Phase 2 reactions from Phase 1 reactions in drug metabolism?

<p>Phase 2 reactions involve significant structural changes (B)</p> Signup and view all the answers

Which species exhibits a pharmacokinetic profile with a clearance rate of 188 mL/kg·hr for meloxicam?

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

How does the liver assist in the drug-excretion process?

<p>Through bile production for elimination (D)</p> Signup and view all the answers

What does the terminal elimination half-life (t1/2) represent?

<p>The time it takes for the plasma concentration of a drug to decrease by half (A)</p> Signup and view all the answers

Which factors primarily influence the rate of drug elimination from the body?

<p>Volume of distribution and clearance (A)</p> Signup and view all the answers

How do phase 1 and phase 2 reactions contribute to metabolism?

<p>Phase 1 reactions often involve hydrolysis or oxidation, while phase 2 reactions involve conjugation. (C)</p> Signup and view all the answers

What is the hepatic first-pass effect?

<p>The significant reduction of drug concentration before it reaches systemic circulation (C)</p> Signup and view all the answers

What does total body clearance (Cl) measure?

<p>The efficiency of the body in eliminating drugs from circulation (A)</p> Signup and view all the answers

Which statement best describes the interaction of clearance and volume of distribution?

<p>Lower clearance rates can lead to increased volume of distribution. (D)</p> Signup and view all the answers

What is typically observed in the concentration-time curve during elimination?

<p>An exponential decline in drug concentration over time (A)</p> Signup and view all the answers

What is renal excretion primarily responsible for?

<p>The filtration and elimination of drugs and their metabolites from the bloodstream (C)</p> Signup and view all the answers

In the context of elimination, what does a first-order process imply?

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

What aspect of pharmacokinetics is emphasized by the c(t) curve?

<p>The dynamics of drug concentration changes over time (C)</p> Signup and view all the answers

What is clearance (Cl) fundamentally defined as?

<p>The ratio of the time rate-of-change of total drug amount to blood concentration (D)</p> Signup and view all the answers

Which characteristic of clearance makes it a suitable parameter for analyzing drug elimination?

<p>It is independent of the drug's elimination mechanisms (C)</p> Signup and view all the answers

In a linear pharmacokinetics system, how is clearance regarded?

<p>As a constant due to first-order kinetics (B)</p> Signup and view all the answers

How can total body clearance (Cl) be computed from a concentration-time curve?

<p>Cl = Dose / Area Under the Curve (AUC) (B)</p> Signup and view all the answers

What does the term 'first-order kinetics' indicate in pharmacokinetics?

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

What does a higher clearance value imply about the body's ability to eliminate a drug?

<p>Greater ability to eliminate the drug from the body (A)</p> Signup and view all the answers

Why is clearance important in determining steady-state plasma concentrations?

<p>It shows the body's ability to maintain drug levels during dosing (A)</p> Signup and view all the answers

Which of the following is a primary application of clearance in pharmacokinetics?

<p>Determining steady-state plasma concentrations (A)</p> Signup and view all the answers

Flashcards

First-order elimination

A process where a constant fraction of the drug is eliminated per unit of time. This means that the rate of elimination is proportional to the concentration of the drug in the body.

Terminal elimination half-life (t1/2)

The time it takes for the blood concentration of a drug to reduce by 50% during the terminal phase of the concentration-time curve.

Terminal elimination rate constant (kel)

A constant that describes the rate of drug elimination during the terminal phase. Higher kel means faster elimination.

What is the relationship between t1/2 and kel?

They are inversely proportional. A longer half-life (t1/2) corresponds to a smaller elimination rate constant (kel), and vice versa. This means a slower elimination rate results in a longer time to reach half the initial concentration.

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How is 't1/2' visualized?

In a concentration-time curve, the time it takes for the concentration to drop by 50% is represented by the half-life (t1/2). This can be observed both on a linear and logarithmic y-axis.

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What does the terminal phase of the concentration-time curve represent?

The terminal phase represents the elimination of the drug from the body after the peak concentration is reached. It follows first-order kinetics, meaning a constant fraction of the drug is eliminated per unit time.

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Why is the terminal phase important?

The terminal phase is essential for understanding the duration of drug action and the time it takes for the drug to be eliminated from the body. This is important for determining dosing intervals and minimizing potential adverse effects.

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How to make a memory tip for drug clearance?

Think of a container of water with a small hole at the bottom. The water drains out over time. The rate at which the water drains is proportional to how much water is left. Likewise, drug clearance is proportional to the amount of drug left in the body.

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Clearance (Cl)

The volume of plasma that is completely cleared of a drug per unit of time.

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Total body clearance (Cl)

The sum of clearance by all organs and tissues that eliminate the drug.

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What are the two phases of metabolism?

Phase 1 reactions introduce or expose a functional group (e.g., -OH, -NH2) on the drug molecule, making it more water-soluble, and phase 2 reactions attach a larger, more polar molecule to the drug.

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Hepatic first-pass effect

When a drug is absorbed from the gastrointestinal tract, it passes through the liver before reaching systemic circulation and is partially metabolized.

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Renal excretion

Excretion of drugs and their metabolites through the kidneys.

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ADME

Absorption, Distribution, Metabolism, and Excretion. It describes the journey of a drug through the body from administration to elimination.

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Concentration-time curve (IV)

A graph showing the drug concentration in plasma over time after intravenous administration.

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First-order elimination kinetics

The rate of elimination is proportional to the drug concentration in the body. This means the drug is eliminated at a constant fraction per unit of time.

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What is the relationship between clearance and volume of distribution?

Clearance (Cl) reflects the efficiency of drug elimination, while the volume of distribution (Vd) reflects how widely a drug distributes in the body. Together they determine how long a drug stays in the body.

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Rate of Elimination

The speed at which a drug is removed from the body.

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Distribution Volume (VD)

The apparent volume of distribution of a drug in the body, reflecting how much of the drug is in the blood versus other tissues.

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Concentration-Time Curve (c(t))

A graph representing the changing concentration of a drug in the blood over time.

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Total Body Clearance

The overall clearance of drug from the entire body, calculated by dividing the drug dose by the area under the concentration-time curve (AUC).

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AUC (Area Under the Curve)

The total area under the concentration-time curve, representing the overall exposure to the drug.

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First-order Kinetics

A process where the rate of elimination is directly proportional to the drug concentration.

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Linear PK Systems

Pharmacokinetic systems where the dose, concentration, and elimination rate are linearly related. Clearance is constant.

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Meloxicam

A nonsteroidal anti-inflammatory drug (NSAID) used for pain relief, known for greater COX-2 selectivity compared to older NSAIDs.

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Pharmacokinetics

The study of how a drug is absorbed, distributed, metabolized, and eliminated from the body.

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Volume of distribution (Vd)

A measure of how widely a drug is distributed throughout the body; a higher Vd indicates a wider distribution.

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Drug clearance (Cl)

A measure of how effectively a drug is removed from the body; a higher Cl indicates faster elimination.

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Half-life (t1/2)

Time taken for the concentration of a drug to reduce by half in the body.

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Metabolism (Biotransformation)

Chemical transformation of a drug into one or more metabolites, often changing its activity or making it easier to eliminate.

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Phase 1 Reactions

Metabolic reactions that typically involve adding or removing functional groups to a drug, making small changes to its structure.

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Phase 2 Reactions

Metabolic reactions that usually involve attaching a large, charged molecule to a drug, greatly altering its properties and making it more water-soluble.

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Drug Interaction

When one drug affects the effectiveness or side effects of another drug.

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Levetiracetam

An anti-epileptic medication, often used to treat seizures in dogs.

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Phenobarbital

Another anti-epileptic medication, commonly prescribed for seizures.

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Drug Metabolism

The process by which the body breaks down and eliminates drugs.

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Enzyme Induction

When a drug, like phenobarbital, increases the activity of enzymes involved in drug metabolism.

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Portal Circulation

The system of blood vessels that carries blood from the intestines to the liver.

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Systemic Circulation

The circulation of blood throughout the body, excluding the lungs.

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Biotransformation

The process of chemically altering a drug within the body.

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Oral vs. IV Administration

Oral administration means taking a drug by mouth, while IV administration means injecting the drug directly into a vein.

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Study Notes

Metabolism and Excretion (Elimination)

  • This lecture covers metabolism and excretion, crucial processes in drug elimination.

  • The presentation outlines the phases of the concentration-time curve (c(t)).

  • Rate of elimination is characterized by the terminal elimination half-life (t1/2), measuring the drug's elimination rate.

  • Clearance (Cl) represents the body's ability to eliminate a drug, quantified by total body clearance (Cltotal).

  • Clearance models, interactions between clearance and volume of distribution (VD), and metabolism reactions (Phase 1 and 2) are key aspects.

  • Hepatic first-pass effect and renal excretion are important aspects of elimination.

  • The interplay between volume of distribution (VD) and clearance (Cl) influences the terminal elimination half-life (t1/2).

  • First-order elimination is typical for drug elimination, allowing for the definition of a half-life.

  • Terminal elimination half-life (t1/2) is inversely proportional to the rate constant (kel).

  • Total body clearance is a composite notion influenced by the sum of specific tissue/organ clearances, such as hepatic and renal clearances.

  • Physiological models of clearance are crucial. They establish relationships between blood flow to a clearing organ and extraction ratio to quantify clearance.

  • The presentation introduces the concept that clearance (Cl) and volume of distribution (VD) are independent factors.

  • Different models for measuring organ-specific clearance are important.

  • Biotransformation pathways like phase 1 and phase 2 reactions are explained.

  • The lecture details the hepatic first-pass effect and its implications on drug concentration in systemic circulation upon oral administration.

  • Examples of drugs like meloxicam and morphine are provided to illustrate their metabolism pathways and pharmacokinetics.

  • An example is given of how drug interactions influence concentration-time profiles, using Levetiracetam as an example.

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Exam 1 - Metabolism & Excretion PDF

Description

This quiz covers essential concepts in metabolism and excretion, crucial for understanding drug elimination. Topics include the rate of elimination, terminal elimination half-life, and the body's clearance mechanisms. Explore the intricacies of hepatic first-pass effect and renal excretion processes.

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