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Questions and Answers
Which factor primarily affects the absorption rate of a drug based on its molecular weight?
Why is a non-ionized drug more likely to be absorbed in the gastrointestinal tract?
How does pH influence drug ionization?
What happens to aspirin in the stomach due to its pKa?
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What is the role of pKa in drug absorption?
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How can urine pH be manipulated for drug excretion in cases of toxicity?
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Which of the following factors can affect drug absorption?
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Which scenario correctly reflects the influence of ionization on drug pharmacokinetics?
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What is the primary effect of drug molecular weight on absorption?
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How does the ionization of a drug influence its ability to diffuse across cell membranes?
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Which statement about the pKa of a drug is correct?
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What happens to aspirin when it is ionized in the alkaline environment of the kidney?
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Which factor would likely decrease the absorption of a drug in the gastrointestinal tract?
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In which condition would urine alkalinization be particularly beneficial?
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What impact does drug formulation have on absorption?
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Which attribute of a drug promotes its absorption in the body?
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Study Notes
Introduction to Pharmacology
- Pharmacology is the study of drugs and their effects on living organisms.
- Pharmacokinetics is the study of what the body does to a drug.
- Pharmacodynamics is the study of what a drug does to the body.
Pharmacokinetics - ADME
- Absorption: the passage of a drug from the site of administration into the bloodstream.
- Distribution: the process of a drug moving from the bloodstream to the tissues and organs
- Metabolism: the process of breaking down drugs in the body, primarily in the liver
- Excretion: the process of removing drugs from the body, mainly via the kidneys
Factors Affecting Drug Absorption
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Drug Factors:
- Molecular Weight: Lower molecular weight drugs absorb more easily.
- Lipophilicity: Lipid-soluble drugs absorb more readily than water-soluble drugs.
- Solubility: Non-ionized drugs are lipid-soluble and can pass through cell membranes easily. Ionized drugs are water-soluble and have difficulty crossing cell membranes.
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pKa:
- The pH of the medium (e.g., body fluid) and the pKa of the drug determine the degree of ionization.
- pKa represents the pH at which 50% of the drug is ionized and 50% is non-ionized.
Clinical Significance of pKa
- In the Gastrointestinal Tract (GIT):
- Aspirin, a weak acid with a pKa of 3.5, is non-ionized in the stomach. This allows it to easily cross the cell membrane and enter gastric mucosal cells where it becomes trapped. This can lead to cell death and peptic ulceration.
- In the Kidneys:
- Drug ionization increases renal excretion.
- To increase excretion of acidic drugs like aspirin, urine can be alkalinized.
- To increase excretion of basic drugs like amphetamine, urine can be acidified.
Introduction to Pharmacology
- Pharmacology is a quantitative study of drugs, specifically how the body processes and responds to them.
- Pharmacokinetic refers to the movement of drugs through the body, encompassing four key processes:
- Absorption
- Distribution
- Metabolism
- Excretion
- Absorption is the initial process where a drug enters the bloodstream from its administration site.
Factors Affecting Drug Absorption
- Factors affecting drug absorption can be categorized into two groups:
- Drug properties
- Patient Factors
Drug Properties
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Molecular weight (MW) plays a crucial role in absorption:
- Lower MW drugs generally exhibit higher absorption rates.
- Higher MW drugs typically show slower absorption.
- Example: Procaine penicillin (PP) is a large molecule and therefore has limited absorption.
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Lipophilicity (lipid solubility): Highly lipid-soluble drugs readily pass through cell membranes and are absorbed more efficiently.
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Solubility: Whether a drug is soluble in water or lipids influences its ability to cross cell membranes:
- Non-ionized drugs are typically lipid-soluble and can easily diffuse across cell membranes.
- Ionized drugs are water-soluble and have difficulty passing through cell membranes.
Ionization and pKa
- Drugs can exist in ionized and non-ionized forms within solutions.
- The degree of ionization depends on:
- pH of the solution
- pKa of the drug (dissociation constant)
- pKa represents the pH at which a drug is 50% ionized and 50% non-ionized.
Acidic vs Basic Drugs
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Acidic drugs:
- Tend to be ionized in basic environments
- Remain non-ionized in acidic environments, leading to higher absorption.
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Basic drugs:
- Tend to be ionized in acidic environments
- Remain non-ionized in basic environments, leading to higher absorption.
Clinical Significance of pKa
-
Gastrointestinal Tract (GIT):
- Aspirin (weak acid, pKa 3.5) remains non-ionized in the acidic stomach, readily crossing cell membranes and entering gastric mucosal cells.
- Aspirin can become trapped within these cells, causing damage and potentially leading to peptic ulceration.
-
Kidney:
- Ionized drugs are more easily excreted by the kidneys. Therefore:
- Alkalinization of urine can enhance the excretion of acidic drugs (e.g., Aspirin overdose).
- Acidification of urine can promote the excretion of basic drugs (e.g., Amphetamine toxicity).
- Ionized drugs are more easily excreted by the kidneys. Therefore:
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Description
Test your knowledge on the basics of pharmacology, including pharmacokinetics and pharmacodynamics. This quiz covers the key concepts of drug absorption, distribution, metabolism, and excretion. Dive into factors affecting drug absorption and see how well you understand the subject.
