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Questions and Answers
What is the primary definition of absorption in drug pharmacokinetics?
What is the primary definition of absorption in drug pharmacokinetics?
What does bioavailability measure in drug absorption?
What does bioavailability measure in drug absorption?
What happens during first pass hepatic metabolism?
What happens during first pass hepatic metabolism?
Why are very hydrophilic drugs poorly absorbed?
Why are very hydrophilic drugs poorly absorbed?
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Which drug property can negatively affect absorption due to pH instability?
Which drug property can negatively affect absorption due to pH instability?
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What is the major site of drug absorption in the gastrointestinal tract?
What is the major site of drug absorption in the gastrointestinal tract?
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For optimal absorption, a drug should possess which of the following properties?
For optimal absorption, a drug should possess which of the following properties?
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What is a significant outcome of the first pass metabolism on drug bioavailability?
What is a significant outcome of the first pass metabolism on drug bioavailability?
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What effect could large volumes of GI contents have on oral drug administration in ruminants?
What effect could large volumes of GI contents have on oral drug administration in ruminants?
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Which routes of administration are considered parenteral?
Which routes of administration are considered parenteral?
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What is a potential adverse effect of parenteral drug administration in food animals?
What is a potential adverse effect of parenteral drug administration in food animals?
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What type of drugs are almost completely absorbed through the skin?
What type of drugs are almost completely absorbed through the skin?
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What factor is important for drug absorption from the respiratory tract?
What factor is important for drug absorption from the respiratory tract?
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Which of the following can impair drug absorption through the intradermal route?
Which of the following can impair drug absorption through the intradermal route?
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What aspect can diminish drug absorption when administering parenterally?
What aspect can diminish drug absorption when administering parenterally?
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Which drug characteristics influence the rate of distribution to various compartments?
Which drug characteristics influence the rate of distribution to various compartments?
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What role does the chemical structure of a drug play in its absorption?
What role does the chemical structure of a drug play in its absorption?
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How is pinocytosis primarily used in drug absorption?
How is pinocytosis primarily used in drug absorption?
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Which drug is specifically mentioned as being actively transported into the renal tubule?
Which drug is specifically mentioned as being actively transported into the renal tubule?
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What is a common characteristic of the IV route of drug administration?
What is a common characteristic of the IV route of drug administration?
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What factor does not significantly limit the absorption rate of drugs via the GI tract?
What factor does not significantly limit the absorption rate of drugs via the GI tract?
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Which statement is true regarding the oral route of drug administration?
Which statement is true regarding the oral route of drug administration?
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What can enhance the absorption of certain drugs when taken orally?
What can enhance the absorption of certain drugs when taken orally?
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Active transport mechanisms are characterized by which of the following?
Active transport mechanisms are characterized by which of the following?
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Which characteristic of drugs affects their ability to penetrate cell membranes?
Which characteristic of drugs affects their ability to penetrate cell membranes?
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What type of drug is primarily bound to albumin?
What type of drug is primarily bound to albumin?
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How does plasma protein binding affect the pharmacologic effect of a drug?
How does plasma protein binding affect the pharmacologic effect of a drug?
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What happens to drug bound to plasma proteins during kidney filtration?
What happens to drug bound to plasma proteins during kidney filtration?
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What is a potential result of competition for binding sites on plasma proteins?
What is a potential result of competition for binding sites on plasma proteins?
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Which drug characteristic enhances the likelihood of redistribution?
Which drug characteristic enhances the likelihood of redistribution?
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What factor contributes to interspecies differences in drug distribution in animals?
What factor contributes to interspecies differences in drug distribution in animals?
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What typically terminates the action of a drug in the body?
What typically terminates the action of a drug in the body?
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What is required for a drug to effectively cross the blood-brain barrier?
What is required for a drug to effectively cross the blood-brain barrier?
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What process allows for the active transport of drugs from cerebrospinal fluid into the blood?
What process allows for the active transport of drugs from cerebrospinal fluid into the blood?
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Which of the following statements about cerebrospinal fluid is true?
Which of the following statements about cerebrospinal fluid is true?
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How do drugs generally cross the placenta?
How do drugs generally cross the placenta?
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What is the effect of inflammation of the brain on drug passage?
What is the effect of inflammation of the brain on drug passage?
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Study Notes
Drug Absorption
- Absorption involves the transfer of drugs from the administration site to blood circulation.
- Rate and efficiency of absorption depend on the route of administration and dosage form.
- Oral administration requires drug dissolution in gastrointestinal fluid and penetration of intestinal epithelial cells, primarily in the duodenum.
- Understanding absorption rates is crucial for predicting the onset of drug action and response magnitude.
Bioavailability
- Bioavailability is the fraction of the administered drug that reaches systemic circulation unchanged.
- Example: If 100 mg of a drug is administered orally and 70 mg is absorbed, bioavailability is 70%.
Factors Influencing Drug Absorption
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First Pass Metabolism:
- Drugs absorbed through the GI tract may be partially metabolized by the liver before reaching systemic circulation, reducing unchanged drug availability.
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Solubility of the Drug:
- Poor absorption occurs in very hydrophilic or extremely hydrophobic drugs, as they cannot easily cross cell membranes.
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Chemical Instability:
- Some drugs are unstable in gastric pH, leading to reduced absorption.
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Active Transport:
- Requires specific chemical structures to utilize carrier molecules for drug absorption, as seen with anticancer drugs utilizing uracil transport systems.
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Pinocytosis:
- Involves engulfing particles or liquids, important for certain polypeptides and immunoglobulins.
Route of Drug Administration
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Different routes require different absorption processes.
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Oral Route:
- Safest administration route but lower bioavailability due to first pass metabolism.
- Factors affecting absorption include gastric contents, blood flow, and GI tract differences across species.
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Parenteral Route:
- Circumvents GI tract absorption; includes IV, IM, SC, and IP.
- Absorption affected by blood flow and vasoconstriction can impair it.
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Skin/Intradermal Route:
- Highly lipid-soluble drugs are mostly absorbed; skin disruptions can impair absorption.
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Respiratory Route:
- Used for gases and volatile anesthetics; particle size is critical for absorption.
Distribution of Drugs
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Dose and Route of Administration:
- Impacts distribution; adequate blood flow is essential.
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Blood Flow:
- Varies widely among tissues; higher flow in organs like the brain, liver, and kidneys.
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Physicochemical Properties:
- Lipid solubility, pH, and molecular size significantly influence drug distribution.
Binding to Plasma Proteins
- Only unbound drugs can cross cell membranes; plasma protein binding is reversible.
- Acidic drugs primarily bind to albumin; basic drugs bind to α1-acid glycoprotein.
- Binding may slow drug concentration achievement but does not prevent access to action sites.
Drug Interactions and Interspecies Differences
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Drug Interactions:
- Occurs when two drugs compete for binding sites on plasma proteins, increasing free drug concentrations and effects.
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Interspecies Differences:
- Variability in drug distribution is observed among different species, influenced by gastrointestinal tract mass.
Drug Redistribution
- Redistribution from high blood flow sites to low can terminate drug action, especially for highly lipid-soluble drugs.
CNS and Transplacental Distribution
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CNS Distribution:
- Limited by the blood-brain barrier, requiring high lipid solubility to pass.
- Active transport mechanisms exist for certain acids and bases in the choroid plexus, affecting CNS drug levels.
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Transplacental Distribution:
- Drugs can cross the placenta via simple diffusion; the degree of transfer varies with drug properties.
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Other Barriers:
- Tissues like the prostate and testicles possess barriers that limit drug concentration.
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Description
Explore the vital concepts of drug absorption and bioavailability in this quiz. Delve into factors that influence how drugs are absorbed into systemic circulation, including the impact of first-pass metabolism. Understanding these principles is essential for predicting drug action and efficacy.
