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Questions and Answers
What is the relationship between drug dosage, drug concentration in plasma, and drug concentration at the site of action, according to the principles of pharmacokinetics and pharmacodynamics?
What is the relationship between drug dosage, drug concentration in plasma, and drug concentration at the site of action, according to the principles of pharmacokinetics and pharmacodynamics?
- Drug dosage determines the drug concentration in plasma, which directly determines the therapeutic response, irrespective of the concentration at the site of action.
- Drug concentration at the site of action is independent of the drug concentration in plasma and is solely determined by the drug dosage.
- Drug dosage influences the drug concentration in plasma, which is in equilibrium with the drug concentration at its site of action. The drug concentration at the site of action ultimately determines the therapeutic response. (correct)
- Drug dosage directly determines the therapeutic response, and the drug concentration in plasma and at the site of action are irrelevant.
Which of the following statements accurately describes the relationship between pharmacokinetics and pharmacodynamics?
Which of the following statements accurately describes the relationship between pharmacokinetics and pharmacodynamics?
- Pharmacokinetics describes 'what the body does to the drug', influencing drug concentration, while pharmacodynamics describes 'what the drug does to the body', relating concentration to effect. (correct)
- Pharmacokinetics and pharmacodynamics are independent processes that do not influence each other.
- Pharmacokinetics describes 'what the drug does to the body', while pharmacodynamics describes 'what the body does to the drug'.
- Pharmacodynamics focuses solely on drug absorption, while pharmacokinetics focuses on drug excretion.
A drug is administered orally but undergoes significant first-pass metabolism. How does this affect the drug's bioavailability and what alternative route of administration could be used to mitigate this effect?
A drug is administered orally but undergoes significant first-pass metabolism. How does this affect the drug's bioavailability and what alternative route of administration could be used to mitigate this effect?
- Increases bioavailability; intramuscular administration.
- Increases bioavailability; intravenous administration.
- Decreases bioavailability; topical administration.
- Decreases bioavailability; sublingual administration. (correct)
A drug is known to be poorly absorbed in the gastrointestinal tract due to its chemical properties. Which of the following factors would most significantly contribute to this poor absorption?
A drug is known to be poorly absorbed in the gastrointestinal tract due to its chemical properties. Which of the following factors would most significantly contribute to this poor absorption?
A patient is taking a medication that is a weak acid. How would increasing the patient's urine pH affect the excretion of this drug, and why?
A patient is taking a medication that is a weak acid. How would increasing the patient's urine pH affect the excretion of this drug, and why?
A drug is highly lipid-soluble. What implications does this have for its ability to cross the blood-brain barrier and its overall distribution in the body?
A drug is highly lipid-soluble. What implications does this have for its ability to cross the blood-brain barrier and its overall distribution in the body?
Only 'free' (unbound) drugs can exert pharmacological effects. What factor primarily determines the amount of free drug available in the body?
Only 'free' (unbound) drugs can exert pharmacological effects. What factor primarily determines the amount of free drug available in the body?
Which statement accurately describes how competition for plasma protein binding sites between two drugs can affect their respective concentrations and effects?
Which statement accurately describes how competition for plasma protein binding sites between two drugs can affect their respective concentrations and effects?
How does the volume of distribution (Vd) relate to the concentration of a drug in the plasma?
How does the volume of distribution (Vd) relate to the concentration of a drug in the plasma?
If a drug has a large volume of distribution, what does this indicate about its distribution in the body?
If a drug has a large volume of distribution, what does this indicate about its distribution in the body?
A drug is metabolized via Phase I and Phase II reactions. What is the primary purpose of these metabolic phases?
A drug is metabolized via Phase I and Phase II reactions. What is the primary purpose of these metabolic phases?
Which of the following best describes the function of Phase I reactions in drug metabolism?
Which of the following best describes the function of Phase I reactions in drug metabolism?
Where do Phase II reactions primarily occur, and what is the typical effect of these reactions on a drug's activity and polarity?
Where do Phase II reactions primarily occur, and what is the typical effect of these reactions on a drug's activity and polarity?
What is the role of Cytochrome P450 (CYP) enzymes in drug metabolism, and how can variations in their activity affect drug responses among individuals?
What is the role of Cytochrome P450 (CYP) enzymes in drug metabolism, and how can variations in their activity affect drug responses among individuals?
A patient is a known 'slow metabolizer' of a drug. If given a standard dose of this drug, how might this affect the drug's concentration in their body and the potential for adverse effects?
A patient is a known 'slow metabolizer' of a drug. If given a standard dose of this drug, how might this affect the drug's concentration in their body and the potential for adverse effects?
One drug can affect the metabolism of another drug. Why is this a critical consideration when prescribing new medications?
One drug can affect the metabolism of another drug. Why is this a critical consideration when prescribing new medications?
What is the primary mechanism by which the kidneys eliminate drugs from the body, and how do lipid solubility and ionization state affect this process?
What is the primary mechanism by which the kidneys eliminate drugs from the body, and how do lipid solubility and ionization state affect this process?
How does compromised renal function influence drug excretion, and what adjustments might be necessary in drug dosing?
How does compromised renal function influence drug excretion, and what adjustments might be necessary in drug dosing?
What is 'first-pass metabolism,' and how does it affect the amount of drug that reaches systemic circulation after oral administration?
What is 'first-pass metabolism,' and how does it affect the amount of drug that reaches systemic circulation after oral administration?
Define 'bioavailability' in the context of pharmacokinetics.
Define 'bioavailability' in the context of pharmacokinetics.
How do you calculate 'apparent volume of distribution'?
How do you calculate 'apparent volume of distribution'?
What is 'elimination half-life,' and why is it a clinically relevant parameter in pharmacokinetics?
What is 'elimination half-life,' and why is it a clinically relevant parameter in pharmacokinetics?
What is 'clearance' in pharmacokinetics, and what factors influence its value?
What is 'clearance' in pharmacokinetics, and what factors influence its value?
According to the fate of a swallowed drug, which processes occur after the drug has been absorbed into the systemic circulation?
According to the fate of a swallowed drug, which processes occur after the drug has been absorbed into the systemic circulation?
A patient has significantly decreased liver function due to cirrhosis. How would this condition likely affect the metabolism and clearance of a drug primarily metabolized by the liver?
A patient has significantly decreased liver function due to cirrhosis. How would this condition likely affect the metabolism and clearance of a drug primarily metabolized by the liver?
An elderly patient often has decreased renal and hepatic function compared to a younger adult. How would you expect this to influence the half-life of a drug that is primarily cleared through these organs?
An elderly patient often has decreased renal and hepatic function compared to a younger adult. How would you expect this to influence the half-life of a drug that is primarily cleared through these organs?
Which route of drug administration is most likely to avoid the first-pass effect?
Which route of drug administration is most likely to avoid the first-pass effect?
A drug that is actively secreted into the renal tubules shows saturation kinetics at high doses. What effect would this saturation have on the drug's clearance as the dose is increased?
A drug that is actively secreted into the renal tubules shows saturation kinetics at high doses. What effect would this saturation have on the drug's clearance as the dose is increased?
A drug causes liver enzyme induction. How will this affect the metabolism of other drugs?
A drug causes liver enzyme induction. How will this affect the metabolism of other drugs?
In which process, related to drug handling, are drugs converted to more water-soluble compounds?
In which process, related to drug handling, are drugs converted to more water-soluble compounds?
Where do drugs that are highly concentrated in tissues generally stay?
Where do drugs that are highly concentrated in tissues generally stay?
To allow for excretion of a drug, what generally needs to happen?
To allow for excretion of a drug, what generally needs to happen?
Flashcards
Pharmacokinetics
Pharmacokinetics
What the body does to the drug; relates dosage to drug concentration in plasma.
Pharmacodynamics
Pharmacodynamics
What the drug does to the body relating drug concentration in tissue to therapeutic response.
Drug Absorption
Drug Absorption
Movement of drug from administration site to measurement site in the body.
Drug Distribution
Drug Distribution
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Drug Metabolism
Drug Metabolism
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Elimination
Elimination
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Disposition
Disposition
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First-pass effect
First-pass effect
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First-pass effect
First-pass effect
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Better
Better
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Highly Polar Drugs
Highly Polar Drugs
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Physicochemical Properties
Physicochemical Properties
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Free Drug
Free Drug
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Volume of distribution
Volume of distribution
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Metabolism
Metabolism
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Phase I Metabolism
Phase I Metabolism
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Phase II Metabolism
Phase II Metabolism
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Individual differences
Individual differences
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Drug interactions
Drug interactions
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Ion Trapping
Ion Trapping
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First-pass metabolism
First-pass metabolism
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Bioavailability
Bioavailability
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Apparent volume of distribution
Apparent volume of distribution
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Elimination half-life
Elimination half-life
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Clearance
Clearance
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Study Notes
- Drug Handling is also known as Pharmacokinetics part 1.
General Scheme for Drug Action
- Drug response relies on concentration at the action site, balancing concentration in blood with dosage.
- Pharmacodynamics relates to the effect of the drug on the body via interaction of cell components that affect cell signaling
- Pharmacokinetics defines what the body does to the drug by relating dosage to the drug's concentration in plasma.
Speed of Onset vs Convenience
- Considerations should be given to both the speed of onset, and convenience when administering drugs
The Fate of a Drug
- Most drugs are taken orally
Pharmacokinetics - ADME
- Key processes in pharmacokinetics include:
- Absorption: Movement from administration site to measurement site.
- Distribution: Reversible transfer into/out of tissues from bloodstream.
- Metabolism: Conversion to a water-soluble form.
- Excretion: Removal of unchanged drug, including biliary excretion
- Elimination is the loss of drug through metabolism and excretion.
- Disposition encompasses all post-absorption processes like distribution and elimination.
Absorption and First Pass Effect
- Drugs taken orally are absorbed and may undergo first pass metabolism, which is pre-systemic elimination.
Factors Affecting Amount of Drug
- Chemical properties such as its stability, polarity, and size affect the amount of drug appearing in systemic circulation.
- Physiological variables such as food intake, gastric pH, and gut motility also affect drug absorption.
pH Effects on Ionization
- Non-ionized drugs cross lipid biological barriers more effectively than ionized forms.
- Acids ionize in basic environments, while bases ionize in acidic environments.
Distribution
- Distribution is influenced by physicochemical properties.
- Highly lipid-soluble drugs cross the blood-brain barrier.
- Unbound drugs diffuse into tissues, produce effects, and are metabolized/excreted.
- Some drugs accumulate in tissues, acting as reservoirs.
Drug Distribution Factors
- Distribution involves reversible transfer from blood to tissues, achieving distribution equilibrium.
- Physicochemical factors include drugs that are small, non-polar and lipid soluble
- Some drugs bind to plasma proteins which include acidic drugs binding to albumin and basic drugs binding to α1-acid glycoprotein
- Only unbound, free drug distributes and exerts pharmacological action.
Free Drug
- Free drug has an active effect.
- Plasma binding proteins are affected by age, inflammatory conditions, and stress.
- Competition for plasma binding sites can be clinically important.
Dose, Volume, and Concentration
- Apparent volume of distribution can be calculated using the following formula: Drug concentration = Drug dose/Volume of distribution
Metabolism
- Polar molecules are readily excreted via the kidneys.
- Non-polar drugs require metabolization into polar forms to allow for excretion.
- Two possible steps include:
- Phase 1: reaction uncovers a (sticky) reactive chemical group.
- Phase 2: reactions attach an additional chemical group [conjugation].
Metabolism - Phase 1
- Phase I reactions are mainly carried out by Cytochrome P450 enzymes.
- These enzymes have a broad spectrum of substrates that overlap with each other and catalyse the reaction DRUG-H + O2 which then yields DRUG-OH
- Some prodrugs are metabolized, such as enalapril being metabolized into enalaprilat.
Metabolism - Phase 2
- Phase II involves conjugation.
- Occurs mainly in the liver.
- Examples include Glucuronidation, Sulphation, Acetylation
- DRUG-glucuronide is typically inactive and polar, facilitating excretion in the bile or urine.
Drug Metabolism - Individual Differences
- Drug metabolism varies among individuals.
- Extremes of age and disease states.
- Genetic variation can lead to fast or slow metabolizers.
- Liver enzyme induction happens slowly at a nuclear level and is long lasting.
- Liver enzyme inhibition happens immediately as a competition for substrate binding sites
Drug Interactions
- One drug can either increase or decrease the metabolism of another.
- It is important to consider drug interactions before prescribing any new drug
Renal Excretion
- Drugs can passively filter or be actively secreted in the kidneys.
- Lipid-soluble drugs are reabsorbed, thus poorly excreted.
- Excretion of ionized drugs is increased by modifying urinary pH relative to the drug's pKa.
- Amount of drug excreted is related to kidney function: Accumulation increases with elevated creatinine.
Pharmacokinetics - Definitions
- Key terms include:
- First pass metabolism: Breakdown of the drug before reaching the systemic circulation after oral administration
- Bioavailability: Fraction of drug reaching systemic circulation
- Apparent volume of distribution: Plasma volume a drug appears to dissolve into
- Elimination half-life: Time for plasma drug amount to decrease by half
- Clearance: Volume of plasma cleared of drug per unit time.
Volume of Distribution Formula
- Volume of distribution = drug dose / drug concentration.
- Volume of distribution is only true at the point of instantaneous distribution
Summary
- ADME (Absorption, Distribution, Metabolism, Excretion) describes what happens to a drug in the body.
- Understanding ADME is important, as it may be affected in individual patients.
- Measures like half-life can predict therapeutic or toxic effects.
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