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Questions and Answers
What is the primary factor that allows a drug to reach steady state in pharmacokinetics?
What is the primary factor that allows a drug to reach steady state in pharmacokinetics?
Which scenario best illustrates the concept of steady state being reached quickly due to short half-life?
Which scenario best illustrates the concept of steady state being reached quickly due to short half-life?
What could be a disadvantage of using long half-life drugs in therapy?
What could be a disadvantage of using long half-life drugs in therapy?
How many half-lives are typically required for a drug to achieve steady state?
How many half-lives are typically required for a drug to achieve steady state?
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Which of the following statements is true regarding the effects of drug half-life?
Which of the following statements is true regarding the effects of drug half-life?
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What is the primary reason that drug concentrations increase when doses are repeated?
What is the primary reason that drug concentrations increase when doses are repeated?
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How many half-lives does it generally take to reach steady state for practical purposes?
How many half-lives does it generally take to reach steady state for practical purposes?
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What happens to the peak, average, and trough drug concentrations when steady state is reached?
What happens to the peak, average, and trough drug concentrations when steady state is reached?
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Which factor primarily determines the time taken to achieve steady state?
Which factor primarily determines the time taken to achieve steady state?
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What percentage of the steady state is achieved after two half-lives?
What percentage of the steady state is achieved after two half-lives?
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What effect does repeating a dose have on plasma concentration if elimination has not been completed?
What effect does repeating a dose have on plasma concentration if elimination has not been completed?
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What is the relationship between elimination rate and drug absorption rate at steady state?
What is the relationship between elimination rate and drug absorption rate at steady state?
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Which of the following is true regarding the impact of a specific dosing regimen on drug effect?
Which of the following is true regarding the impact of a specific dosing regimen on drug effect?
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What is a key risk associated with drugs that have short half-lives when administered intermittently?
What is a key risk associated with drugs that have short half-lives when administered intermittently?
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Which of the following drugs is an example of one that typically has a short half-life?
Which of the following drugs is an example of one that typically has a short half-life?
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What is the main influence of a drug's half-life on dosing regimens?
What is the main influence of a drug's half-life on dosing regimens?
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When are continuous infusions or inhalations of drugs typically required?
When are continuous infusions or inhalations of drugs typically required?
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What happens to the plasma concentrations of a drug administered intermittently with larger dose intervals?
What happens to the plasma concentrations of a drug administered intermittently with larger dose intervals?
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In which scenario is stable drug concentration most critical?
In which scenario is stable drug concentration most critical?
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What is a common characteristic of drugs with longer half-lives compared to those with shorter half-lives?
What is a common characteristic of drugs with longer half-lives compared to those with shorter half-lives?
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How do trough concentrations relate to treatment efficacy in short half-life drugs?
How do trough concentrations relate to treatment efficacy in short half-life drugs?
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Study Notes
Pharmacokinetics
- Pharmacokinetics is the study of "what the body does to a drug"
- It differs from pharmacodynamics, which is the study of "what a drug does to the body"
- Pharmacokinetics involves the rate and extent of drug absorption, distribution, metabolism, and excretion
- It explains drug concentration fluctuations over time after administration
- It's critical for determining appropriate dosage regimens and predicting drug responses
Learning Outcomes
- Students should be able to explain
- What pharmacokinetics is
- How drugs are absorbed into the body
- Drug distribution in the body
- Drug metabolism in the body
- Drug excretion from the body
- Relationship between drug concentration and time (single dose)
- Relationship between drug concentration and time (repeated doses)
Drug Absorption
- Drugs can be absorbed orally, buccally, sublingually, rectally, intravenously, intramuscularly, subcutaneously, or by inhalation
- Oral (PO) administration involves drug absorption across the small intestine's mucosa, then the portal circulation, and eventually systemic circulation
- Buccal or sublingual administration avoids portal circulation, with direct absorption into systemic circulation
- Intravenous (IV) injection delivers the drug directly into the bloodstream, bypassing absorption processes.
- Factors affecting absorption include route, drug properties (e.g., lipid solubility), and physiological conditions.
Drug Distribution
- For a drug to have its desired pharmacodynamic effects, it must reach its target site at an adequate concentration
- Distribution depends on factors like blood flow, drug properties, and special barriers (e.g., blood-brain barrier).
- Drug molecules move across cell membranes through processes like passive diffusion, facilitated diffusion, or active transport.
- Distribution influences drug action by affecting the concentration at the target site.
Drug Metabolism
- Metabolism, often in the liver, transforms drugs into metabolites
- It helps inactivating drugs and making them more water-soluble for excretion
- Metabolism can be categorized into Phase I (e.g., oxidation, reduction, hydrolysis) and Phase II (e.g., glucuronidation, sulfation, or acetylation) reactions
- Liver is the primary organ of drug metabolism due to high blood flow and presence of enzymes like Cytochrome P450 (CYP) system
- Interactions with other drugs or substances can influence metabolism.
Drug Excretion
- Kidneys are the major organ for excreting drug metabolites
- Drugs can be eliminated through glomerular filtration, tubular secretion, and tubular reabsorption
- Other routes include biliary excretion (into bile, then feces), respiration (for volatile drugs), sweat, and breast milk.
- Factors like urine pH and presence of other substances in the body may affect the rate of drug excretion
- enterohepatic circulation is also essential in eliminating drugs.
Concentration-Time Relationships (Single Dose)
- First-order kinetics: The rate of elimination is proportional to the drug concentration
- The rate of elimination is constant at a specific time interval (e.g. 50% decrease per hour)
- Describes the decrease in drug concentration over time
- Exponential decline in drug concentration in the plasma
Concentration-Time Relationships (Repeated Doses)
- Zero-order kinetics: A constant amount of drug is eliminated per unit of time
- The rate of elimination becomes saturated (e.g., enzyme systems are maxed, metabolite removal is limited by capacity)
- Elimination is not based on concentration and the accumulation of the drug may lead to undesirable concentrations and potential toxicity.
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Description
This quiz explores the fundamental principles of pharmacokinetics, focusing on how the body interacts with drugs. It covers aspects such as absorption, distribution, metabolism, and excretion of medications. Students will also learn about drug concentration fluctuations over time and how this information is essential for dosage determination.
