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Questions and Answers
Define passive and active drug absorption.
Define passive and active drug absorption.
Passive absorption relies on diffusion along a concentration gradient, while active absorption requires energy to move substances against their gradient.
How does Fick’s law of diffusion relate to passive drug absorption?
How does Fick’s law of diffusion relate to passive drug absorption?
Fick’s law states that the rate of diffusion is proportional to the concentration gradient, influencing the absorption rate of drugs passively.
Calculate the percent of drug nonionized and ionized for a weak acid or weak-base drug using the Henderson–Hasselbalch equation.
Calculate the percent of drug nonionized and ionized for a weak acid or weak-base drug using the Henderson–Hasselbalch equation.
Percent nonionized = $\dfrac{1}{1 + 10^{(pKa - pH)}} \times 100$; percent ionized = $\dfrac{10^{(pKa - pH)}}{1 + 10^{(pKa - pH)}} \times 100$.
Define transcellular and paracellular drug absorption.
Define transcellular and paracellular drug absorption.
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How can stomach emptying time and GI transit time alter the rate and extent of drug absorption?
How can stomach emptying time and GI transit time alter the rate and extent of drug absorption?
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Explain the effect of food on GI physiology and systemic drug absorption.
Explain the effect of food on GI physiology and systemic drug absorption.
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Describe the various transporters and how they influence pharmacokinetics of drug disposition in the GI tract.
Describe the various transporters and how they influence pharmacokinetics of drug disposition in the GI tract.
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What is the pH-partition hypothesis?
What is the pH-partition hypothesis?
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How might a disease that causes changes in intestinal blood flow and/or motility affect drug absorption?
How might a disease that causes changes in intestinal blood flow and/or motility affect drug absorption?
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List the major factors that affect drug absorption from oral and non-oral routes of drug administration.
List the major factors that affect drug absorption from oral and non-oral routes of drug administration.
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What methods may be used to study oral drug absorption from the GI tract?
What methods may be used to study oral drug absorption from the GI tract?
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Study Notes
Drug Absorption Overview
- Drug absorption is classified into passive and active absorption mechanisms.
- Passive absorption involves movement across membranes due to concentration gradients, described by Fick's law of diffusion.
- Active absorption requires energy to move drugs against their concentration gradient.
Ionization and Drug Absorption
- The Henderson–Hasselbalch equation helps calculate the percent ionized and nonionized of weak acids and bases.
- The ionization state significantly affects absorption since only nonionized drugs can easily cross membranes.
Absorption Pathways
- Transcellular absorption occurs through cells, while paracellular absorption occurs between cells.
- Examples include hydrophilic drugs absorbing paracellularly, and lipophilic drugs absorbing transcellularly.
Gastrointestinal (GI) Tract Dynamics
- The anatomy of the GI tract plays a crucial role in drug absorption.
- Factors like stomach emptying time and GI transit time influence the rate and extent of absorption.
Food Effects on Absorption
- Food can alter GI physiology, impacting systemic drug absorption positively or negatively.
Drug Transport Mechanisms
- Various transporters exist in the GI tract that influence pharmacokinetics, affecting how drugs are absorbed into the bloodstream.
pH-Partition Hypothesis
- The pH-partition hypothesis suggests that gastrointestinal pH and the drug's pKa affect absorption.
- Drugs are more likely to be absorbed when nonionized, which often occurs at specific pH levels.
Impact of Disease on Absorption
- Diseases that affect intestinal blood flow or motility can significantly alter drug absorption patterns.
Factors Affecting Drug Absorption Routes
- Major factors include chemical properties of the drug, nature of the drug formulation, and the absorption site’s anatomy and physiology.
Evaluation of Drug Absorption
- Methods exist for studying oral drug absorption from the GI transit, helping to understand therapeutic outcomes.
Drug Product Design Considerations
- Drug design must consider therapeutic objectives, application site, and systemic absorption goals.
- For systemic action, drugs should achieve consistent absorption; for local action, minimal systemic absorption is preferable.
Extended-Release Formulations
- Extended-release products are designed to keep the drug localized while allowing for slow release over time.
Importance of Biopharmaceutics
- Understanding biopharmaceutics is essential for developing effective drug products by correlating drug properties with the intended therapeutic effect.
Pharmacist's Role
- Pharmacists need to comprehend the relationships between drug dosage, efficacy, adverse reactions, drug-drug, and drug-nutrient interactions for effective patient care.
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Description
Test your understanding of Chapter 4 from Shargel and Yu's Applied Biopharmaceutics and Pharmacokinetics. This chapter focuses on the physiologic factors related to drug absorption, including passive and active mechanisms, Fick’s law of diffusion, and the Henderson-Hasselbalch equation. Take the quiz to solidify your grasp of these key concepts in pharmacokinetics.
