Podcast
Questions and Answers
Why is drug absorption through the gastrointestinal tract among the best understood processes?
Why is drug absorption through the gastrointestinal tract among the best understood processes?
- Absorption of drugs through the gastrointestinal tract is always complete.
- Gastric acid and digestive enzymes inactivate drugs in the gut lumen. (correct)
- Biological phospholipid membranes are impermeable to lipid-soluble drugs.
- First-pass metabolism does not occur in the gut wall or liver.
What explains why the bioavailability of an orally administered drug is typically less than 100%?
What explains why the bioavailability of an orally administered drug is typically less than 100%?
- First-pass metabolism occurs only in the kidneys.
- The drug is impermeable to biological phospholipid membranes.
- Absorption through the gastrointestinal tract is always complete.
- Inactivation within the gut lumen and pre-systemic metabolism affect drug availability. (correct)
Which process explains why most drugs are absorbed incompletely unless administered intravenously?
Which process explains why most drugs are absorbed incompletely unless administered intravenously?
- Absence of any inactivation mechanisms within the gut lumen
- Complete absorption through lipid-soluble membranes
- Pre-systemic ('first-pass') metabolism in the gut wall and liver (correct)
- Systemic effect exerted by most drugs
How can the bioavailability of a drug formulation be measured experimentally?
How can the bioavailability of a drug formulation be measured experimentally?
What defines bioavailability in terms of drug administration?
What defines bioavailability in terms of drug administration?
What is a key factor that influences the drug formulation's disintegration, dispersion, and dissolution in the gastrointestinal tract?
What is a key factor that influences the drug formulation's disintegration, dispersion, and dissolution in the gastrointestinal tract?
In what year did an epidemic of phenytoin intoxication occur in Australia due to changes in the drug's excipient?
In what year did an epidemic of phenytoin intoxication occur in Australia due to changes in the drug's excipient?
What happened when the manufacturing process of digoxin in the UK was changed?
What happened when the manufacturing process of digoxin in the UK was changed?
What factor led to confusion when restoring the original manufacturing conditions of digoxin in the UK?
What factor led to confusion when restoring the original manufacturing conditions of digoxin in the UK?
Why did differences in bioavailability lead to an epidemic of phenytoin intoxication in Australia?
Why did differences in bioavailability lead to an epidemic of phenytoin intoxication in Australia?
Study Notes
Drug Absorption and Bioavailability
- Drug absorption through the gastrointestinal tract is well understood due to extensive research on factors influencing this process, including pH, solubility, and gastrointestinal motility.
- Bioavailability of orally administered drugs is typically less than 100% due to factors like first-pass metabolism, incomplete absorption, and degradation in the gastrointestinal tract.
- Incomplete absorption of most drugs, unless given intravenously, is primarily explained by the first-pass effect, where a portion of the drug is metabolized before reaching systemic circulation.
Measuring Bioavailability
- Experimental measurement of bioavailability can be performed through pharmacokinetic studies, comparing the concentration of drug in systemic circulation after different routes of administration.
- Bioavailability is defined as the proportion of a drug that enters systemic circulation when it is administered and is available for activity, usually expressed as a percentage.
Factors Influencing Drug Formulation
- A key factor influencing drug formulation's disintegration, dispersion, and dissolution in the gastrointestinal tract is the drug's physicochemical properties, including particle size and solubility.
Case Studies
- An epidemic of phenytoin intoxication occurred in Australia in 1996 due to changes in the excipients used in the drug formulation, leading to variations in absorption rates.
- Changes in the manufacturing process of digoxin in the UK resulted in an increase in toxicity among patients due to altered drug bioavailability.
- Confusion arose when restoring original manufacturing conditions of digoxin due to the variability in patient responses and differences in bioavailability linked to the new production methods.
- Differences in bioavailability in phenytoin led to an epidemic of intoxication because the adjustments in excipients caused significant fluctuations in drug absorption, resulting in dangerous therapeutic levels.
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Description
Test your knowledge about drug absorption, bioavailability, bioequivalence, generic vs. proprietary prescribing, and different routes of drug administration. Understand how the rate and extent of penetration of biological phospholipid membranes affect drug absorption.
