Pharmacokinetics Overview
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Questions and Answers

What is the principal organ of drug metabolism?

  • Kidneys
  • Lungs
  • Liver (correct)
  • Heart

Which component of the cytochrome P450 system is essential for its function?

  • Protein
  • Nucleotide
  • Lipid
  • Haem (correct)

What is first-pass metabolism primarily associated with?

  • Intramuscular routes
  • Topical applications
  • Oral drug administration (correct)
  • Injection routes

Which of the following drugs is subject to extensive first-pass metabolism?

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

What contributes to the loss of drug doses during first-pass metabolism?

<p>Metabolism in the small bowel and liver (C)</p> Signup and view all the answers

Which of the following has the largest volume of total body water in a 70 kg adult?

<p>42 litres (A)</p> Signup and view all the answers

What is an effect of first-pass metabolism on orally administered drugs?

<p>Decrease in bioavailability (A)</p> Signup and view all the answers

Where does portal blood pass after being absorbed from the gastrointestinal tract?

<p>Through the sinusoids of the liver lobules (A)</p> Signup and view all the answers

What does pharmacokinetics primarily refer to?

<p>The handling of the drug by the body (D)</p> Signup and view all the answers

Which of the following factors is NOT mentioned as influencing pharmacokinetic handling of a drug?

<p>Genetic predisposition (B)</p> Signup and view all the answers

What outcome might result from impaired renal function according to pharmacokinetics?

<p>Delayed excretion of the drug (B)</p> Signup and view all the answers

Which aspect of drug response does pharmacodynamics specifically address?

<p>Drug effect and clinical response (A)</p> Signup and view all the answers

How can external factors like food influence pharmacokinetics?

<p>By altering drug metabolism (C)</p> Signup and view all the answers

What is a potential outcome of an excessive response to a drug?

<p>Increased drug concentration at the site of action (D)</p> Signup and view all the answers

In pharmacokinetics, which factor is related to variability in drug responses among different patients?

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

What can lead to a suboptimal drug response during therapy?

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

What occurs when a drug is administered at a high enough dose to saturate its primary metabolic pathway?

<p>An alternative metabolic pathway becomes more active. (C)</p> Signup and view all the answers

What is the consequence of paracetamol overdose regarding its metabolism?

<p>Production of a toxic metabolite via phase I metabolism. (D)</p> Signup and view all the answers

Why might the route of drug administration affect metabolism significantly?

<p>Different routes target specific tissues more efficiently. (D)</p> Signup and view all the answers

What happens to a proportion of an orally administered drug?

<p>It may not be absorbed due to its characteristics. (D)</p> Signup and view all the answers

What is the primary organ responsible for excreting low molecular weight compounds?

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

Which of the following compounds is primarily excreted through bile?

<p>High molecular weight compounds (D)</p> Signup and view all the answers

What is first-pass metabolism?

<p>Metabolism of the drug that occurs in the small intestine and liver before systemic circulation. (D)</p> Signup and view all the answers

How are drugs typically absorbed after oral administration?

<p>They enter the portal circulation and may undergo first-pass metabolism. (B)</p> Signup and view all the answers

What is the primary focus of pharmacokinetics?

<p>The absorption, distribution, metabolism, and excretion of drugs (D)</p> Signup and view all the answers

Which phase of pharmacokinetics involves the body's handling of drugs after absorption?

<p>Distribution phase (B)</p> Signup and view all the answers

What does the acronym A-D-M-E in pharmacokinetics stand for?

<p>Absorption, Distribution, Metabolism, Excretion (A)</p> Signup and view all the answers

Which of the following best describes pharmacodynamics?

<p>The study of how the body affects drugs (C)</p> Signup and view all the answers

What is one key reason pharmacokinetics is important for prescribers?

<p>To understand the optimal dosing schedule (D)</p> Signup and view all the answers

Which organ is primarily involved in the metabolism of drugs?

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

Which of the following best describes the relationship studied in pharmacokinetics?

<p>Time and plasma drug concentration (A)</p> Signup and view all the answers

How are drugs or their metabolites typically excreted from the body?

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

What does the law of mass action propose regarding chemical reactions?

<p>The rate of a reaction is directly proportional to reactant concentrations. (D)</p> Signup and view all the answers

How does drug concentration affect the metabolism of drugs in the cytochrome P450 system?

<p>Rate of metabolism is proportional to concentration. (C)</p> Signup and view all the answers

What does first-order kinetics imply in drug elimination processes?

<p>A constant fraction of drug is eliminated in a given time. (D)</p> Signup and view all the answers

What characterizes the drug elimination process for most drugs?

<p>It is high capacity and does not saturate at high doses. (D)</p> Signup and view all the answers

What relationship does glomerular filtration have with drug concentration in plasma?

<p>It is directly proportional to plasma concentration. (C)</p> Signup and view all the answers

How does increasing drug concentration affect the rate of elimination?

<p>The rate of elimination increases with higher concentration. (A)</p> Signup and view all the answers

What happens to metabolic reactions as the concentration of reactants increases?

<p>They drive faster metabolic reactions. (D)</p> Signup and view all the answers

What aspect of drug elimination does the law of mass action support?

<p>Higher concentrations result in faster elimination rates. (D)</p> Signup and view all the answers

What does the elimination rate constant, k, help to describe in relation to drug concentration?

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

What happens to plasma concentration after one half-life?

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

What is the relationship between dose increases and plasma concentration in first-order kinetics?

<p>Plasma concentration increases predictably with dose increases (D)</p> Signup and view all the answers

What is a common characteristic of drugs that follow zero-order kinetics?

<p>Elimination occurs at a constant rate regardless of the dose (C)</p> Signup and view all the answers

Which statement accurately reflects the implications of zero-order kinetics for prescribers?

<p>Dose titration becomes highly unpredictable (D)</p> Signup and view all the answers

In pharmacokinetics, what term is used to describe the time taken for the plasma concentration to halve?

<p>Half-life (t½) (A)</p> Signup and view all the answers

What can happen when a drug is administered at higher toxic doses?

<p>Metabolizing enzymes may become saturated (C)</p> Signup and view all the answers

Why is it said that for most drugs given in therapeutic doses, elimination is a first-order process?

<p>Metabolizing enzymes work at maximum efficiency without saturation (B)</p> Signup and view all the answers

Flashcards

What is pharmacokinetics?

Pharmacokinetics is the study of how the body processes a drug, including absorption, distribution, metabolism, and excretion.

Absorption

Absorption is the process of a drug moving from the site of administration (e.g., stomach, muscle) into the bloodstream.

Distribution

Distribution is the process of the drug moving from the bloodstream to different tissues and organs.

Metabolism

Metabolism is the process of the body breaking down the drug into smaller molecules, usually in the liver.

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Excretion

Excretion is the process of the body eliminating the drug or its metabolites, usually through the kidneys in urine.

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What is pharmacodynamics?

Pharmacodynamics is the study of how a drug affects the body, including its mechanism of action and therapeutic effects.

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Why is pharmacokinetics important for prescribers?

Pharmacokinetics helps prescribers understand how to dose medications effectively, considering factors like absorption, distribution, metabolism, and excretion.

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What does ADME stand for?

ADME stands for Absorption, Distribution, Metabolism, and Excretion - the four key processes of pharmacokinetics.

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Pharmacokinetics

The study of how the body absorbs, distributes, metabolizes, and eliminates drugs. Basically, it's how the body processes a drug.

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Pharmacodynamics

The study of how drugs affect the body. Essentially, it's the drug's impact on the body's functions.

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Drug Dosage Regimen

The schedule for administering a drug, which includes the dose, frequency, and route of administration. It's the plan for how the drug is given.

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Drug Concentration in Plasma

The amount of drug present in the blood plasma. This is a key measure in understanding how the drug is distributed in the body.

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Drug Concentration Around Site of Action

The amount of drug present at the target tissue or organ where it's supposed to exert its effects.

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Physiological Factors

These are intrinsic characteristics of the patient, such as age, sex, body weight, and organ function, that influence how a drug is handled.

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External Factors

Factors outside the body that can affect drug pharmacokinetics, such as food, other drugs, and environmental conditions.

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Adverse Drug Reactions

Unexpected or unwanted reactions to a drug that can range from mild to severe. These reactions can occur due to variations in how the body handles the drug.

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Volume of Distribution (Vd)

The apparent volume of fluid into which a drug distributes in the body. It reflects how readily a drug distributes to tissues compared to plasma.

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Liver

The primary organ responsible for drug metabolism. It contains enzymes that break down drugs into inactive forms.

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Cytochrome P450 System

A group of enzymes in the liver responsible for metabolizing drugs. It's a major player in drug breakdown.

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First-Pass Metabolism

The breakdown of a drug by enzymes in the gut wall and liver before it reaches the systemic circulation. This can significantly reduce the amount of drug available.

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Oral Bioavailability

The proportion of a drug dose that reaches the systemic circulation after oral administration. It's affected by first-pass metabolism.

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Verapamil and Glyceryl Trinitrate

Examples of drugs that undergo significant first-pass metabolism, leading to low oral bioavailability.

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Gastrointestinal Tract

The digestive system, including the stomach, small bowel, and large bowel. Drugs are first absorbed here.

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Portal Circulation

The blood vessels connecting the gastrointestinal tract to the liver. This is where drugs go after absorption in the gut.

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Drug Metabolism Saturation

When a high drug dose overwhelms the primary metabolic pathway, alternative pathways become more active.

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Paracetamol Overdose

An example of drug metabolism saturation. Excess paracetamol saturates the normal pathway, leading to higher levels of a toxic metabolite.

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Phase I & II Metabolism

Drug metabolism often proceeds in two phases. Phase I modifies the drug, making it more water-soluble. Phase II conjugates the drug, preparing it for excretion.

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Drug Administration Route

The way a drug enters the body can significantly affect its metabolism. Oral drugs are processed in the gut and liver before reaching the bloodstream.

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Drug Excretion

Removal of drugs and their metabolites from the body.

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Kidney Excretion

The kidney is the primary organ for excreting small, water-soluble compounds via filtration and active secretion.

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Bile Excretion

The bile, produced by the liver, excretes large, fat-soluble compounds (over 400-500 Da) into the feces.

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Law of Mass Action

This law states that a chemical reaction's rate is directly proportional to the concentration of reactants. In simpler terms, the higher the concentration of the substances involved, the faster the reaction will occur.

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Drug Metabolism in the Liver

The process of breaking down drugs in the liver, mainly by enzymes like cytochrome P450. This process is crucial for eliminating drugs from the body.

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Glomerular Filtration

The process of filtering blood in the kidneys to remove waste products, including drugs. The amount of drug filtered is proportional to its concentration in the blood.

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First-Order Kinetics

A type of drug elimination where a constant percentage of the drug is removed from the body per unit time. This means that the higher the drug concentration, the faster the elimination rate.

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Drug Elimination

The process by which the body gets rid of drugs, primarily through metabolism in the liver and excretion by the kidneys.

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High Capacity Elimination

For most drugs, the body can eliminate them efficiently, even at high doses, without becoming overwhelmed. This means the elimination process isn't limited by the amount of drug present.

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Therapeutic Range

The range of drug concentrations in the body that produces the desired therapeutic effects without causing excessive side effects.

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Effect of Concentration on Elimination

The rate of drug elimination is directly related to the concentration of the drug in the body. Higher concentrations lead to faster elimination due to the law of mass action.

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Half-life (t½)

The time it takes for the plasma concentration of a drug to decrease by 50%.

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Exponential Kinetics

The rate of drug elimination is proportional to the amount of drug present in the body, resulting in a predictable decline in concentration over time.

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Zero-Order Kinetics (Saturation Kinetics)

The rate of drug elimination is constant, regardless of the drug concentration. This happens when the enzymes responsible for metabolism are saturated.

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Dose Titration

Adjusting the dose of a drug to achieve a desired therapeutic effect.

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Concentration-Time Curve

A graph that plots a drug's concentration in plasma over time.

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Predictable Effect of Dosage

Doubling the dose of a drug generally leads to a doubling of the plasma concentration at all time points after dosing.

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Concentration-Response Relationship

The relationship between the drug concentration in the body and the resulting effect.

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Study Notes

Pharmacokinetics

  • Pharmacokinetics is the study of 'what the body does to a drug'
  • It differentiates from pharmacodynamics (what a drug does to the body)
  • It describes how the dosage regimen relates to the pharmacological effects
  • It explains how drug concentration varies over time after administration
  • It involves the rate and extent of drug absorption and distribution to body tissues
  • It describes the rate and pathways by which drugs are eliminated from the body through metabolism and excretion
  • It describes the relationship between time and plasma drug concentration

Learning Outcomes

  • Explain what pharmacokinetics is
  • Describe how drugs are absorbed into the body
  • Describe how drugs are distributed in the body
  • Describe how drugs are metabolised in the body
  • Describe how drugs are excreted from the body
  • Explain the relationship between drug concentration and time (single dose)
  • Explain the relationship between drug concentration and time (repeated doses)

Four Phases of Pharmacokinetics

  • Absorption of drugs into the body
  • Distribution of drugs to the tissues
  • Metabolism of drugs, notably in the liver
  • Excretion of drugs, notably from the kidney

Routes of Drug Administration

  • Oral (PO): drug swallowed
  • Buccal: placed between the lip and gum
  • Sublingual: placed beneath the tongue
  • Rectal (PR): administered rectally
  • Intravenous (IV): directly into a vein
  • Intramuscular (IM): into muscle tissue
  • Subcutaneous (SC): underneath the skin
  • Inhalation (INH): via the airways

Oral Administration

  • A proportion of the drug dose is bioavailable
  • Drugs are affected by: gastric acid, food interactions, physicochemical characteristics
  • First-pass metabolism (intestinal wall and liver) may limit absorption

Drug Distribution

  • Drugs must reach the site of action at sufficient concentration
  • Factors affecting distribution include: molecular size, lipid solubility, ionisation, binding to plasma proteins, rate of blood flow, and special barriers like the blood-brain barrier
  • Drug concentrations in various body compartments (plasma, interstitial fluid, intracellular fluid) influence distribution

Drug Metabolism

  • The liver is the principal organ of metabolism
  • The cytochrome P450 system is a superfamily of enzymes in the smooth endoplasmic reticulum of hepatocytes
  • The liver's anatomical relationship with the gastrointestinal tract impacts first-pass metabolism
  • Other sites of metabolism include the lungs, kidneys, and skin
  • Metabolism converts drugs into a less active or more water-soluble form for excretion
  • Metabolism is categorized into Phase I and Phase II reactions

Drug Excretion

  • The kidneys are the most important site for excretion of low molecular weight compounds
  • Biliary excretion removes large molecular weight compounds
  • Lungs excrete volatile anaesthetic gases and small amounts of other compounds
  • Other excretion routes include tears, sweat, saliva, and breast milk

Drug Concentration and Time (Single Dose)

  • First-order kinetics: The rate of elimination is proportional to the drug concentration.
  • Zero-order kinetics: The rate of elimination is constant, regardless of the drug concentration (common in high doses).

Drug Concentration and Time (Repeated Doses)

  • Repeated doses lead eventually to a steady state, where the rate of drug administration equals the rate of drug elimination.
  • Steady state is reached after 5 half-lives.
  • Factors affecting repeated dose pharmacokinetics include half-life and dosing interval.

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Related Documents

Pharmacokinetics Lecture Notes PDF

Description

This quiz explores the fundamental concepts of pharmacokinetics, including drug absorption, distribution, metabolism, and excretion. Understand the relationship between drug concentration and time to master how the body interacts with medications. Ideal for students in pharmacology or related fields.

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