Questions and Answers
Which of the following is a major factor that affects the absorption of a drug from the gastrointestinal tract?
What is the primary mechanism of active transport in drug absorption?
What is the primary mechanism of renal excretion?
Which of the following factors can affect the bioavailability of a drug?
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What is the definition of absolute bioavailability?
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Which of the following is an example of a formulation factor that can affect bioavailability?
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What is the definition of relative bioavailability?
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How does creatinine clearance affect drug disposition?
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What is the significance of enterohepatic circulation in drug pharmacokinetics?
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In the context of the first pass effect, what is the primary site of drug metabolism?
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Which factor does NOT favor drug absorption?
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Which mechanism of absorption involves competitive interaction for carrier molecules?
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Which characteristic of a drug would most likely hinder its absorption through cell membranes?
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What is a major consequence of enterohepatic recycling on drug dosing?
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How does pinocytosis specifically contribute to drug absorption?
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Which factor is least likely to affect biliary excretion of a drug?
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Study Notes
Pharmacokinetics
Absorption
- Process by which a drug enters the bloodstream
- Factors affecting absorption:
- Route of administration (oral, IV, topical, etc.)
- Drug formulation (tablet, capsule, solution, etc.)
- pH and enzyme activity in the GI tract
- Blood flow to the absorption site
- Types of absorption:
- Passive diffusion
- Active transport
- Facilitated diffusion
Distribution
- Process by which a drug disperses throughout the body
- Factors affecting distribution:
- Blood flow to different tissues
- Drug binding to plasma proteins
- Lipid solubility of the drug
- Tissue permeability
- Types of distribution:
- Central compartment (blood and highly perfused organs)
- Peripheral compartment (less perfused tissues)
Metabolism
- Process by which a drug is converted into a metabolite
- Factors affecting metabolism:
- Enzyme activity (e.g. Cytochrome P450)
- Genetic variations in enzyme function
- Induction or inhibition of enzymes by other drugs
- Types of metabolism:
- Phase I reactions (oxidation, reduction, hydrolysis)
- Phase II reactions (conjugation)
Excretion
- Process by which a drug or its metabolites are eliminated from the body
- Factors affecting excretion:
- Kidney function (glomerular filtration, tubular secretion)
- Liver function (biliary excretion)
- pH of the urine
- Types of excretion:
- Renal excretion (kidneys)
- Hepatic excretion (liver)
- Other routes (lungs, skin, etc.)
Bioavailability
- The fraction of an administered dose that reaches the systemic circulation
- Factors affecting bioavailability:
- Absorption rate and extent
- First-pass effect (metabolism by the liver before reaching the systemic circulation)
- Formulation and dosage form
- Types of bioavailability:
- Absolute bioavailability (comparison to IV administration)
- Relative bioavailability (comparison to a reference drug or formulation)
Pharmacokinetics
Absorption
- The process by which a drug enters the bloodstream, influenced by the route of administration, drug formulation, pH and enzyme activity in the GI tract, and blood flow to the absorption site
- Types of absorption include passive diffusion, active transport, and facilitated diffusion
Distribution
- The process by which a drug disperses throughout the body, affected by blood flow to different tissues, drug binding to plasma proteins, lipid solubility, and tissue permeability
- Distribution occurs in two compartments:
- Central compartment (blood and highly perfused organs)
- Peripheral compartment (less perfused tissues)
Metabolism
- The process by which a drug is converted into a metabolite, influenced by enzyme activity (e.g. Cytochrome P450), genetic variations in enzyme function, and induction or inhibition of enzymes by other drugs
- Metabolism occurs in two phases:
- Phase I reactions (oxidation, reduction, hydrolysis)
- Phase II reactions (conjugation)
Excretion
- The process by which a drug or its metabolites are eliminated from the body, influenced by kidney function (glomerular filtration, tubular secretion), liver function (biliary excretion), and pH of the urine
- Types of excretion include:
- Renal excretion (kidneys)
- Hepatic excretion (liver)
- Other routes (lungs, skin, etc.)
Bioavailability
- The fraction of an administered dose that reaches the systemic circulation, influenced by absorption rate and extent, first-pass effect, formulation, and dosage form
- Types of bioavailability include:
- Absolute bioavailability (comparison to IV administration)
- Relative bioavailability (comparison to a reference drug or formulation)
Pharmacokinetics Overview
- Plasma concentration (Cp) indicates drug effectiveness and guides dosing strategies.
- Determines dose adjustments for enhancing effectiveness while minimizing toxicity.
Factors Influencing Response
- Effect influenced by dose (bioavailability), age, weight, genetic factors, and organ function.
- Concomitant medications can alter pharmacokinetics due to interactions.
Adverse Effects in Absorption
- Drugs can be affected by food absorption, stomach acid degradation, enzyme activity, and GI metabolism.
First Pass Effect
- Liver enzymes metabolize drugs significantly, reducing bioavailability for orally administered substances.
Bioavailability Influences
- Factors include dosage form (e.g., tablet, IV), manufacturer quality, excipients, and drug dissolution characteristics.
- Differences in generic versus brand name products can also affect bioavailability.
Drug Absorption Principles
- Drugs must traverse lipid membranes to enter systemic circulation.
- Membranes are hydrophobic, necessitating lipid solubility for effective absorption.
Liver Metabolism
- Conjugation enhances drug water solubility for renal or biliary elimination, commonly via glucuronic acid.
- Cytochrome P450 family (especially CYP3A) is vital for drug metabolism, affecting drug interactions.
P-Glycoprotein Function
- A membrane transporter that pumps lipophilic drugs out of cells, contributing to drug resistance during chemotherapy.
- Present in liver, kidney, blood-brain barrier, and placenta, influencing drug absorption and disposition.
Pharmacokinetic Variability
- Affected by age, genetic polymorphism, diseases (like liver failure), nutrition, and hormones.
Impacts of Disease
- Conditions such as liver failure complicate drug dosage adjustments.
- Congestive heart failure affects drug absorption and distribution significantly.
Gender Differences
- Limited studies on gender pharmacokinetics; hormonal differences affect drug metabolism and clearance.
- Women generally require different dosing due to metabolic variances and hormonal influence.
Impact of Gender on Pharmacokinetics
- Women exhibit slower gastric motility and altered absorption rates.
- Distribution differences arise from body composition variations, affecting drug volume distribution.
- Renal elimination rates are lower in women, impacting drug clearance.
Drug Absorption Favorability
- Optimal absorption requires uncharged, nonpolar drugs with low molecular weight and high lipid solubility.
Mechanisms of Drug Absorption
- Passive diffusion is the most common, with active transport involving specific carriers relevant in various body regions.
- Facilitated diffusion and pinocytosis are additional mechanisms facilitating absorption.
Enterohepatic Recycling
- Mechanism involving biliary excretion and intestinal reabsorption leads to prolonged drug presence in circulation and multiple concentration peaks.
- The process may depend on chemical traits and biotransformation characteristics.
Summary of Key Points
- Understanding pharmacokinetics and factors affecting drug absorption, metabolism, and elimination is crucial for effective and safe medication administration.
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Description
This quiz covers the processes of absorption and distribution of drugs in the body, including factors affecting these processes and types of absorption.
