Introduction to Pharmacology
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Questions and Answers

What effect does valproate have on phenytoin levels?

  • Increases protein binding of phenytoin.
  • Decreases free phenytoin levels.
  • Increases free phenytoin levels. (correct)
  • No effect on phenytoin levels.

Which enzyme group is primarily involved in Phase I metabolism?

  • Cytochrome P450 enzymes. (correct)
  • Aldose reductases.
  • Glucuronosyltransferases.
  • Esterases.

What is the primary site of drug metabolism in the human body?

  • Lungs.
  • Liver. (correct)
  • Kidneys.
  • Gut mucosa.

Which of the following statements is true regarding drug elimination?

<p>Elimination can occur through both metabolism and excretion. (C)</p> Signup and view all the answers

What characteristic must a drug possess to easily cross the blood-brain barrier?

<p>Lipid solubility. (C)</p> Signup and view all the answers

What characteristic defines an ideal drug?

<p>Predictable and reversible effects (D)</p> Signup and view all the answers

Which of the following is NOT a source of natural drugs?

<p>Synthetic sources like prednisolone (A)</p> Signup and view all the answers

Which name is used to identify a drug by its chemical structure?

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

What does the term 'pharmacokinetics' primarily refer to?

<p>The time-course of drugs in the body (A)</p> Signup and view all the answers

Which statement is true regarding drug absorption?

<p>Rate of absorption influences the drug's availability in the bloodstream (C)</p> Signup and view all the answers

What is a common characteristic of semisynthetic drugs?

<p>They are partially chemically modified from natural sources (D)</p> Signup and view all the answers

What role does the absorption rate constant (ka) play in pharmacology?

<p>Determines the rate at which a drug is delivered to circulation (D)</p> Signup and view all the answers

What is required for orally, rectally, or vaginally administered drugs to be absorbed?

<p>They must disintegrate and dissolve in body fluids. (C)</p> Signup and view all the answers

Which mechanism of drug absorption involves movement against a concentration gradient?

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

Which drug is specifically an example of one using passive diffusion for absorption?

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

What role does lipid solubility play in drug absorption?

<p>It facilitates easier passage across cell membranes. (C)</p> Signup and view all the answers

What type of transport uses carriers without the direct use of energy (ATP)?

<p>Facilitated passive diffusion (A)</p> Signup and view all the answers

Which of the following drugs primarily utilizes active transport for absorption?

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

What is a distinguishing feature of enteric coated drugs, such as aspirin?

<p>They resist liberation in the stomach. (D)</p> Signup and view all the answers

In which type of absorption method does the cell membrane form a vesicle to transport particles?

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

Which of the following is NOT a factor influencing the rate of passive diffusion?

<p>Presence of active transport mechanisms (B)</p> Signup and view all the answers

What is the main purpose of first-pass metabolism?

<p>To metabolize drugs before they reach systemic circulation (A)</p> Signup and view all the answers

Which of the following drugs requires dosage adjustments due to first-pass metabolism effects?

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

What is indicated by an absolute bioavailability (F) of 1?

<p>The drug is completely available in systemic circulation (D)</p> Signup and view all the answers

Which body compartment contains the fluid that is mainly found surrounding cells?

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

How is bioequivalence defined?

<p>The comparison of bioavailability between alternative formulations of the same drug (C)</p> Signup and view all the answers

Which factor does NOT influence the rate and extent of drug distribution?

<p>Drug's chemical structure (D)</p> Signup and view all the answers

Which factor is NOT included in the definition of bioavailability?

<p>Metabolism of the drug after systemic circulation (D)</p> Signup and view all the answers

What is the significance of Volume of Distribution (Vd) in clinical settings?

<p>It helps in predicting the effectiveness of haemodialysis. (D)</p> Signup and view all the answers

What is the correct equation for calculating absolute bioavailability?

<p>AUC non-intravenous divided by AUC intravenous in % terms (D)</p> Signup and view all the answers

If a drug has high plasma protein binding, what would be the expected Volume of Distribution (Vd)?

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

What is a potential consequence of first-pass metabolism for orally administered drugs?

<p>Reduced therapeutic effectiveness (A)</p> Signup and view all the answers

What is a possible consequence of a patient taking aspirin while on warfarin?

<p>Increased risk of bleeding (C)</p> Signup and view all the answers

Which type of drug administration is expected to have a bioavailability less than one?

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

Which of the following best describes apparent Volume of Distribution (Vd)?

<p>The theoretical volume that would be required to contain all of the drug in the body at plasma concentration (C)</p> Signup and view all the answers

In which compartment is blood plasma found?

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

Which of the following factors does NOT lead to a large Volume of Distribution (Vd)?

<p>High plasma protein binding (A)</p> Signup and view all the answers

What is the primary reason only the free form of a drug can exert pharmacological effects?

<p>It is not bound to proteins or tissues. (D)</p> Signup and view all the answers

How is the effective plasma concentration (Cp) of a drug calculated for determining loading dose?

<p>Cp = Loading dose / Vd (A)</p> Signup and view all the answers

Which plasma protein predominantly binds acidic drugs such as warfarin?

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

What is the primary factor affecting the permeability of tissues to drug molecules?

<p>Polarity of the drug (A)</p> Signup and view all the answers

Flashcards

Drug

A chemical or biological substance used to treat, cure, prevent, or diagnose a disease. It can be a poison at extreme doses. An ideal drug is effective, safe, selective, reversible, predictable, and easy to administer.

Natural Drug Sources

Drugs derived from nature, including plants (like digitalis and morphine), animals (like insulin), and minerals (like kaolin).

Synthetic Drugs

Man-made drugs created in laboratories. Examples include prednisolone, pholcodine, fentanyl, and pethidine.

Semisynthetic Drugs

Drugs made by modifying natural substances. Examples include sulphonamides from bacteria, thiazide diuretics from plants, heroin, and artemisinin derivatives.

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Drug Naming

Drugs have different names: chemical (based on structure), generic (official name), and brand (trade name).

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Pharmacokinetics

The study of how a drug's concentration changes in the body over time. It looks at how the drug is absorbed, distributed, metabolized, and excreted (ADME).

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Absorption

The process of a drug moving from where it enters the body (administration site) to where it's measured (usually blood). It's characterized by the rate of absorption, absorption rate constant, and area under the concentration curve (AUC).

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Drug Liberation

The process where a drug's dosage form breaks down and releases the active ingredient into the body fluids for absorption.

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Enteric Coated Drugs

Drugs designed to resist breakdown in the stomach and release the drug in the intestine. This helps prevent irritation to the stomach lining.

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Absorption Via Passive Diffusion

Movement of drugs across cell membranes from an area of high concentration (like the gut) to low concentration (like the blood).

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Factors Affecting Passive Diffusion

Lipid solubility (ability to dissolve in fats), molecular size (small is better), and degree of ionization (electric charge) affect how easily a drug crosses cell membranes.

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Facilitated Passive Diffusion

The movement of drugs across cell membranes with the help of carrier proteins, but without using energy.

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Active Transport

Movement of drugs against a concentration gradient using energy. Often occurs at specific sites in the small intestine.

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Pinocytosis

A process where the cell membrane engulfs (wraps around) fluid or particles and pulls them inside. This is a potential mechanism for drug absorption.

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ADME

A process that describes how the body handles a drug – Absorption, Distribution, Metabolism, and Excretion.

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Protein Binding Displacement

When a drug with a higher affinity for protein binding sites displaces another drug, increasing the free concentration of the displaced drug.

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High Protein Binding Drugs

Drugs that are predominantly bound to plasma proteins, leaving only a small fraction of the drug free to exert its pharmacological effect.

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What characteristics must a drug possess to cross the blood brain barrier?

The drug must be lipid-soluble and have a low molecular weight to pass through the tight junctions of the brain capillaries.

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Drug Metabolism Phases I & II

Two phases involved in the breakdown of drugs: Phase I - modification by oxidation, reduction, or hydrolysis; Phase II - conjugation with polar molecules.

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Drug Clearance (CL)

The volume of blood cleared of a drug per unit time, indicating the efficiency of elimination.

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First-Pass Metabolism

The breakdown of a drug by the liver and gut wall before it reaches the bloodstream.

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Pre-systemic Metabolism

Another term for the metabolic process where a drug is broken down before reaching the systemic circulation.

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First-Pass Effect

The reduction in a drug's bioavailability due to metabolism before reaching the bloodstream.

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Bioavailability

The percentage of a drug dose that reaches the bloodstream.

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Bioequivalence

The comparison of bioavailability between different formulations of the same drug.

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Intravenous Route

Administration of a drug directly into a vein, bypassing the digestive system.

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Absolute Bioavailability

The percentage of a drug dose reaching the bloodstream compared to an intravenous dose.

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AUC (Area Under Curve)

A measure of the total amount of drug in the bloodstream over time.

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Intravascular Compartment

Fluid within blood vessels, including plasma.

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Extravascular Compartment

Fluid surrounding cells, including interstitial fluid and tissue fluid.

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Drug Distribution

The reversible movement of a drug between the bloodstream and other body compartments (like tissues and organs). This process determines how much drug reaches its target and how long it stays in the body.

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Volume of Distribution (Vd)

The apparent volume a drug occupies in the body, assuming the drug concentration is evenly distributed. It helps determine how much drug is needed to reach a desired effect.

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What influences drug distribution?

Factors that influence drug distribution include: 1) Blood flow to tissues, 2) Binding of the drug to plasma proteins and tissues, and 3) The drug's ability to cross cell membranes.

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Small Vd

Indicates that a drug stays mostly contained in the bloodstream and doesn't distribute widely into tissues. It is often associated with high plasma protein binding.

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Large Vd

Indicates the drug distributes widely into tissues, often binding to proteins or fat. This can lead to a lower concentration in the blood.

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Plasma Protein Binding

Drugs can bind to proteins in the bloodstream, like albumin. Only unbound drugs can exert their pharmacological effect.

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What happens when drugs compete for binding?

If two drugs bind to the same protein, the drug with a higher affinity will likely displace the other drug, leading to increased free drug and potentially toxicity or altered effects.

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Clinical Importance of Vd

Vd impacts how drugs are administered and eliminated. Knowing Vd helps determine appropriate dosages and if therapies like dialysis are effective.

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Loading Dose

An initial larger dose given to quickly raise drug concentration in the plasma to achieve a therapeutic effect. It is often calculated using Vd.

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Haemodialysis

A medical procedure to remove waste products and excess fluid from the blood. It can be used in drug overdose to eliminate drugs, but its effectiveness depends on Vd.

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Study Notes

Introduction to Pharmacology

  • Pharmacology is the study of drugs and their interactions with living systems.
  • It has two main divisions: pharmacokinetics and pharmacodynamics.

What is Pharmacodynamics?

  • Pharmacodynamics studies the effects of drugs on the body.
  • It involves the mechanisms and processes by which drugs exert their effects.
  • An example is how paracetamol works to relieve a headache.

What is Pharmacokinetics?

  • Pharmacokinetics is the study of how the body affects the drug.
  • It involves the time course of drugs within the body, including absorption, distribution, metabolism, and excretion (ADME).
  • It describes the movement of a drug into, within, and out of the body.

Sources of Drugs

  • Drugs come from various sources.
  • Natural sources include plants (e.g., digitalis, belladonna, morphine), animals (e.g., insulin), and minerals (e.g., iron).
  • Synthetic sources include laboratory created compounds (e.g., prednisolone).
  • Semisynthetic drugs are modified natural sources (e.g., penicillin).
  • Recombinant DNA technology may also be used to produce drugs.

Naming of Drugs

  • Drugs have three primary names: chemical, generic, and brand.
  • Chemical names describe the drug's chemical structure.
  • Generic names are used by scientific bodies (e.g., Aspirin, Paracetamol, Pethidine).
  • Brand names are used by manufacturers to identify their specific product (e.g., Tylenol, Viagra).

Absorption

  • Absorption is the process by which a drug moves from the administration site to the measurement site (usually the blood).
  • Factors that affect absorption rate include: liberation time, drug form, molecular size, degree of ionization, pH, and the presence of food.
  • Drugs given intravenously have 100% bioavailability because they go directly into the blood.
  • Absorption rate constant (ka) and Area under the concentration curve (AUC)
  • Absorption via different methods/routes include passive diffusion, transport via facilitated passive diffusion, and transport by active transport.
  • Rate of absorption depends on rate of drug liberation and also the physiological environment at the administration site
  • Enteric coated drugs are designed to resist liberation in the stomach, and are designed to be absorbed in the intestines by being swallowed whole.
  • Factors like presence of food, diseases in the gut (like malabsorption and achlorhydria) can affect the absorption rate.

First-pass Metabolism

  • First-pass metabolism (FPM), also called pre-systemic metabolism, is the breakdown of orally administered drugs in the gut wall or liver before entering the systemic circulation.
  • FPM may result in total or partial inactivation of the drug.
  • Bioavailability is the fraction of the administered dose reaching the systemic circulation.
  • Bioequivalence is the comparison of bioavailability of different formulations of the same drug.

Body Compartments and Drug Distribution

  • The body is divided into intravascular (blood plasma), extravascular (interstitial/tissue fluid), and intracellular (fluid within cells) compartments.
  • Drug distribution depends on the drug's chemical properties and membrane permeability.
  • Volume of distribution (Vd) describes the theoretical volume of fluid in which a drug would have to be distributed to create the observed blood plasma concentration.
  • A high volume of distribution often means the drug is bound to tissues rather than blood.
  • High protein binding can cause lower volume of distribution and low protein binding causes higher volume of distribution.
  • Hepatic disease may increase the half-life, whilst renal disease can slow down excretion.

Plasma Binding proteins

  • Many drugs bind to plasma proteins, mainly albumin.
  • Only the unbound (free) form of a drug can interact with its targets.
  • Changes to protein binding levels can alter drug effect, and can result in displacement interactions.
  • Drug-protein binding interactions are reversible and rapid.

Blood-Brain Barrier

  • The blood-brain barrier protects the central nervous system by limiting drug penetration.

Elimination

  • Elimination is the irreversible loss of drug from the body.
  • Primary sites of elimination include the kidneys, liver, lungs, and in some cases, through milk or feces.
  • Renal excretion involves glomerular filtration, renal tubular excretion, and renal tubular reabsorption.
  • Half-life describes the time it takes for the drug concentration to reduce by half.
  • Diseases like kidney disease slow down elimination of drugs.

Metabolism

  • Metabolism is the chemical conversion of one chemical form to another, either an activation or inactivation process.
  • Liver (rich in enzymes) and other sites (kidney, lungs, gut mucosa) are involved in metabolism.
  • Phase I reactions (e.g., oxidation, reduction, hydrolysis) often introduce a reactive site for Phase II metabolism.
  • CYP enzymes (most importantly CYP450) are the primary oxidases that metabolize a wide range of drugs.
  • Enzyme families like CYP exist as isoforms, which may differ in activity across different individuals and populations.
  • Metabolism is influenced by genetics (fast or slow metabolizers) and by diseases like liver disease
  • Phase II reactions (e.g., glucuronidation, sulfation, acetylation, amino acid conjugation, glutathione conjugation) make metabolites more water-soluble and readily excreted.
  • Reactive metabolites may cause toxicity.

Clinical relevance

  • Changes in absorption, distribution, metabolism, and excretion can change the efficacy and safety of a drug.
  • Dosage adjustments may be necessary for individuals with impaired liver or kidney function.

Important Concepts

  • Bioavailability
  • Bioequivalence

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Description

This quiz explores the foundations of pharmacology, including pharmacodynamics and pharmacokinetics. You will learn about how drugs affect the body and the processes involved in drug absorption and metabolism. Additionally, discover the various sources from which drugs originate.

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