Questions and Answers
Which organ is primarily responsible for drug metabolism?
What is the primary route for the excretion of drugs?
What process occurs to oral medications before they enter systemic circulation?
Which route of drug administration involves injecting directly into skeletal muscle?
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Which organ plays the most minor role in drug elimination?
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After metabolism in the liver, where can modified drugs go?
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What is a characteristic of subcutaneous drug administration?
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Which type of medication can be eliminated through the lungs?
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What does pharmacokinetics primarily describe?
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Which process in pharmacokinetics is primarily concerned with the breakdown of a drug by the body?
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What factors determine the concentration of a drug in systemic circulation?
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How does pharmacodynamics differ from pharmacokinetics?
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Which organ is primarily associated with the excretion process in pharmacokinetics?
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What role does the route of administration play in pharmacokinetics?
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Which component of pharmacokinetics is NOT directly involved in the administration of the drug?
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What is the effect of biotransformation on a drug?
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How does St. John’s Wort affect the systemic circulation of pharmaceuticals?
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What is the bioavailability of drugs administered intravenously as a bolus?
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What is indicated by the relationship between plasma drug level and pharmacological response?
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Why do drugs administered by routes other than intravenous take longer to reach maximum plasma concentration?
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What happens to drugs after they are absorbed into the circulation?
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What does the area under the plasma concentration-time curve (AUC) evaluate?
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How is oral bioavailability (F) determined?
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Which of the following drugs has low oral bioavailability due to extensive first-pass hepatic metabolism?
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What is the significance of reaching a maximum concentration (Cmax) after drug administration?
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What happens after the Cmax is reached during drug absorption?
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Why are nitroglycerin tablets taken sublingually?
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What range can the bioavailability (F) of a drug assume?
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What is the effect of substantial first-pass metabolism on drug response?
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What effect does a higher pKA have on the fraction of a weakly acidic drug that is uncharged?
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How does a lower pH affect the fraction of a weakly acidic drug in its uncharged form?
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In which body compartment is the pH the lowest?
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What happens to a weakly acidic drug in a more alkaline environment?
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What clinical role does the concept of drug 'trapping' play?
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How is the urine pH manipulated to aid in amphetamine overdose treatment?
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What effect does intravenous ammonium chloride have in amphetamine overdose cases?
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Why is blood pH tightly buffered?
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Study Notes
Pharmacokinetics Overview
- Quantitative analysis of drug disposition involves absorption, distribution, metabolism (biotransformation), and excretion (ADME).
- Drug concentration in systemic circulation and at active sites determines the intensity of effects.
- Pharmacokinetics differs from pharmacodynamics, which examines how drugs produce biological changes.
Drug Absorption and Distribution
- Drug absorption involves movement from administration site into the bloodstream, which distributes to various body organs.
- Key organs for elimination include the liver (primary site for metabolism) and kidneys (main site for excretion).
- Other elimination sites include the lungs, skin, and gastrointestinal tract.
Routes of Drug Administration
- Oral administration allows medications to be absorbed through the gastrointestinal tract into portal circulation, subject to first-pass metabolism before entering systemic circulation.
- Intravenous (IV) administration delivers drugs directly into systemic circulation, achieving nearly 100% bioavailability.
- Intramuscular (IM) and subcutaneous (SC) routes involve injections that are absorbed into the blood through muscle or subcutaneous tissue, respectively.
Influence of pH on Drug Absorption
- The pH of body compartments (e.g., stomach pH 1.9-2.6; intestine pH 6.4-7.6; blood pH ~7.4) affects the distribution of weakly acidic or basic drugs.
- A weak acid is more likely to be trapped in alkaline environments, as higher pH reduces the concentration of uncharged protonated form.
- Drug overdose cases highlight the importance of drug trapping; for example, acidifying urine can help excrete amphetamine more effectively.
Bioavailability and the AUC Concept
- The area under the concentration-time curve (AUC) is crucial for evaluating drug absorption extent.
- Oral bioavailability (F) is defined by comparing AUC after oral and intravenous administration, ranging from 0 (no absorption) to 1 (complete absorption).
- Low oral bioavailability (e.g., nitroglycerin) can be attributed to extensive first-pass metabolism, leading to alternate routes like sublingual administration to bypass liver metabolism.
Drug-Drug Interactions and Metabolism Variability
- Significant variability in the concentration of drugs in systemic circulation, particularly for drugs with substantial first-pass metabolism.
- Co-administration of other drugs can alter hepatic biotransformation, as seen with St. John's Wort inducing the CYP3A4 enzyme, reducing systemic concentrations of certain pharmaceuticals.
Relationship Between Blood Levels and Drug Response
- Clinical pharmacokinetics posits a correlation between plasma or blood drug levels and pharmacological or toxic responses.
- Systemic blood drug concentration often reflects the concentration at sites of action, guiding therapeutic outcomes.
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Description
This quiz covers the basics of pharmacokinetics, focusing on the absorption, distribution, metabolism, and excretion of drugs. Understanding these processes is essential for determining drug concentration in the body and its related effects. Test your knowledge on foundational concepts in drug disposition.
