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Questions and Answers
What is the primary aim of pharmacokinetics?
What is the primary aim of pharmacokinetics?
Which factor does NOT significantly affect the absorption of drugs?
Which factor does NOT significantly affect the absorption of drugs?
What defines bioavailability in pharmacokinetics?
What defines bioavailability in pharmacokinetics?
Which of the following characteristics is crucial for a drug to effectively reach its intended site of action?
Which of the following characteristics is crucial for a drug to effectively reach its intended site of action?
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What does the term 'prodrug' refer to?
What does the term 'prodrug' refer to?
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Which of the following processes is primarily involved when a drug is broken down into smaller metabolites?
Which of the following processes is primarily involved when a drug is broken down into smaller metabolites?
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What is NOT a mechanism of drug movement across membranes?
What is NOT a mechanism of drug movement across membranes?
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Which statement about drug absorption is accurate?
Which statement about drug absorption is accurate?
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What is the relationship between lipid solubility and drug absorption rate?
What is the relationship between lipid solubility and drug absorption rate?
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Which type of molecules generally exhibit poor permeability across membranes due to their size and polarity?
Which type of molecules generally exhibit poor permeability across membranes due to their size and polarity?
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Which process involves the transport of substances against their concentration gradient and requires energy?
Which process involves the transport of substances against their concentration gradient and requires energy?
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Which statement accurately reflects the nature of facilitated diffusion?
Which statement accurately reflects the nature of facilitated diffusion?
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Which molecules are primarily absorbed through simple diffusion?
Which molecules are primarily absorbed through simple diffusion?
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What is true regarding the Henderson–Hasselbalch equation in relation to weak acids and bases?
What is true regarding the Henderson–Hasselbalch equation in relation to weak acids and bases?
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Which method is used for engulfing large molecules such as proteins or toxins?
Which method is used for engulfing large molecules such as proteins or toxins?
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Which transport method is characterized by the dependency on concentration gradients without saturation?
Which transport method is characterized by the dependency on concentration gradients without saturation?
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Which molecules are considered to have high permeability across biological membranes?
Which molecules are considered to have high permeability across biological membranes?
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What is the primary function of the large intestine?
What is the primary function of the large intestine?
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Which factor reduces the amount of drug reaching systemic circulation when administered orally?
Which factor reduces the amount of drug reaching systemic circulation when administered orally?
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What signifies 100% bioavailability of a drug?
What signifies 100% bioavailability of a drug?
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Which of the following does NOT affect drug distribution?
Which of the following does NOT affect drug distribution?
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What does bioavailability specifically measure in pharmacology?
What does bioavailability specifically measure in pharmacology?
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What is an example of a factor that influences capillary permeability?
What is an example of a factor that influences capillary permeability?
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What defines the effective dose of a drug?
What defines the effective dose of a drug?
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Which physiological factor does NOT directly contribute to enhanced drug absorption in the intestine?
Which physiological factor does NOT directly contribute to enhanced drug absorption in the intestine?
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What is the primary reason why the intestine is favored as the main site for drug absorption?
What is the primary reason why the intestine is favored as the main site for drug absorption?
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How does the presence of food in the gastrointestinal tract affect drug absorption?
How does the presence of food in the gastrointestinal tract affect drug absorption?
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What factor significantly reduces the absorption of ionized drugs such as tetracycline in the presence of food?
What factor significantly reduces the absorption of ionized drugs such as tetracycline in the presence of food?
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Which of the following statements about the intestine's structure is false?
Which of the following statements about the intestine's structure is false?
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What characteristic of the intestinal environment helps drugs remain in a unionized state?
What characteristic of the intestinal environment helps drugs remain in a unionized state?
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What role does the dissolution and solubility of solid dosage forms play in drug absorption?
What role does the dissolution and solubility of solid dosage forms play in drug absorption?
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In what condition would accelerated gastric emptying likely result in increased drug absorption?
In what condition would accelerated gastric emptying likely result in increased drug absorption?
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What is one of the primary effects of high permeability in the intestine on drug absorption?
What is one of the primary effects of high permeability in the intestine on drug absorption?
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What is the key difference between facilitated diffusion and active transport?
What is the key difference between facilitated diffusion and active transport?
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Which statement accurately describes active transport?
Which statement accurately describes active transport?
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In which condition would passive diffusion be preferred over active transport?
In which condition would passive diffusion be preferred over active transport?
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Why is active transport considered 'uphill transport'?
Why is active transport considered 'uphill transport'?
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Which of the following processes requires carrier-mediated transport?
Which of the following processes requires carrier-mediated transport?
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What distinguishes facilitated diffusion from passive diffusion?
What distinguishes facilitated diffusion from passive diffusion?
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How does active transport interact with metabolic poisons?
How does active transport interact with metabolic poisons?
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What role do carrier proteins play in carrier-mediated transport systems?
What role do carrier proteins play in carrier-mediated transport systems?
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In which situation would facilitated diffusion occur?
In which situation would facilitated diffusion occur?
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Why is it important for substances to undergo active transport?
Why is it important for substances to undergo active transport?
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Study Notes
Course Information
- Course name: PHARM 225
- Instructor: Dr. Amira Badr
- Email: [email protected]
Objectives
- Students will be able to identify pharmacokinetics.
- Students will be able to define absorption.
- Students will be able to analyze factors affecting absorption.
- Students will be able to identify drug movement mechanisms across membranes.
- Students will be able to define bioavailability.
Relationship Between Pharmacokinetics and Pharmacodynamics
- Pharmacokinetics: the time course of drug absorption, distribution, metabolism, and excretion.
- Primary goals of pharmacokinetics; enhance efficacy and decrease toxicity.
- Pharmacodynamics: relationship between drug concentration at the site of action and resulting effect.
Pharmacokinetics Principle
- In practical therapeutics, a drug must reach its intended site of action at a sufficient concentration.
- Prodrugs are drug derivatives that require enzymatic or chemical transformation to release the active parent drug.
- Prodrugs are used to improve physicochemical or pharmacokinetic properties of pharmacological compounds.
Pharmacokinetics
- Absorption: movement of an unchanged drug from administration site to systemic circulation to reach site of action.
- Distribution: transfer of the drug from one location to another within the body.
- Metabolism: process in which drugs are altered and broken down into smaller substances (metabolites).
- Elimination (Excretion): removal of drug from body fluids (e.g., urine, bile, sweat, saliva, tears, feces, breast milk).
Pharmacokinetics (Absorption)
- Movement of Drugs: Regardless of the administration route (except IV), drugs must pass through multiple biological membranes to reach site of action.
- Bilayer of amphipathic lipids: forms a barrier in biological membranes.
- Factors Affecting Absorption:
- Molecular size
- Polarity
- Partition coefficient
- pH at administration site
- Blood flow
- Surface area
- Drug stability
- Drug formulation
- Contact time (e.g., gastric emptying rate)
Properties of Drugs (Absorption)
- Absorption rate depends on drug lipid solubility and particle size.
- Polarity estimates the partition coefficient (ratio of drug solubility in lipids to water).
- Higher lipid solubility means faster absorption.
- Smaller molecules are absorbed more rapidly.
- The membranes of biological membranes are very permeable to O2, CO2, N2O and H2O.
- Large polar molecules (e.g., sugars, amino acids, phosphorylated intermediates) have poor permeability and require carrier proteins.
Movement of Substances Across Cell Membranes
- Gases (e.g., O2, CO2)
- Hydrophobic molecules
- Small polar molecules (e.g., H2O)
- Large polar molecules
- Charged molecules (e.g., ions)
Pharmacokinetics (Absorption)
- Many drugs (weak acids or bases) ionization varies with pH (Henderson-Hasselbalch equation).
- Only uncharged (unionized) species can diffuse across lipid membranes.
Movement of Substances Across Cell Membranes (Passive Transfer)
- Passive transfer: No energy, non-saturable
- Filtration: Hydrodynamic pressure gradients, low MW, water-soluble
- Simple diffusion: Higher concentration to lower concentration. Lipid-soluble
- Factors Determining Passive Transfer Rate
- Membrane permeability
- Concentration gradient
- Molecular size
- Lipid solubility
- Membrane permeability
Specialized Transport
- Facilitated diffusion: higher concentration to lower concentration, no energy, saturable (protein carrier-mediated).
- Example: tetracycline
- Active transport: against concentration gradient, needs energy, saturable (protein carrier-mediated).
- Example: levodopa, 5-fluoro-uracil, 5-bromouracil
- Endocytosis: engulfing large molecules (e.g., proteins, toxins).
- Example: botulinum and diphtheria
Passive Diffusion
- Also known as non-ionic diffusion.
- Depends on the concentration difference across the membrane
- Absorption of 90% of drugs.
- Driving force is the concentration gradient or electrochemical gradient
- Water, urea, and small lipids move by concentration gradient
Carrier-Mediated Transport Mechanism
- Involves a carrier protein that reversibly binds solute molecules.
- Carrier-solute complex crosses the membrane.
- Solute released, carrier returns to original position to accept new solute molecules.
- Two types: facilitated diffusion (no energy, with the concentration gradient) and active transport (energy required, against the concentration gradient).
Facilitated Diffusion
- This mechanism's driving force is the concentration gradient (downhill transport).
- In this system, no energy is involved.
- It is not inhibited by metabolic poisons that interfere with energy production.
- Example: fructose
Active Transport
- More important than facilitated diffusion.
- Driving force is against the concentration gradient (uphill transport).
- Energy (ATP) is required for the process.
- Inhibited by metabolic poisons that interfere with energy production.
- Example of substances transported: Minerals, sugars, and amino acids
Drug Absorption, Active vs. Passive
- Active transport: Energy-dependent, carrier-mediated, against concentration gradient, shows carrier saturation kinetics.
- Passive transport: Energy-independent, no carrier involved, along the concentration gradient, no saturation kinetics.
Pinocytosis (Endocytosis)
- This process is important in the absorption of oil-soluble vitamins and nutrients.
- Absorption mechanism that takes in fluids and particles.
Other Factors Affecting GIT Absorption
- Blood flow to absorptive site: greater blood flow increases absorption.
- Total surface area of absorptive site: larger surface area increases absorption.
- Contact time at absorptive site: faster gastric emptying increases absorption, while diarrhea reduces it.
- Food presence: reduces/delays drug absorption.
- Formulation factors: solid dosage forms require dissolution and solubility, aqueous solutions are absorbed quicker.
Factors Affecting GIT Absorption (Stomach)
- Small surface area for drug absorption due to lack of villi and microvilli.
- Variation in gastric emptying time affects drug absorption.
- Acid-labile drugs must not come into contact with the stomach's acidic environment.
Factors Affecting GIT Absorption (Intestine)
- Large surface area for drug absorption due to villi and microvilli.
- 7 meters long, approximately 2.5-3 cm in diameter.
- High blood flow compared to the stomach.
- pH range (5-7.5) is favorable for most drugs to remain unionized.
- Slow peristaltic movement and long transit time.
- High permeability.
Factors Affecting GIT Absorption (Large Intestine)
- Major function is to absorb water, and eliminate semi-solid feces.
- Few drugs are absorbed in this region.
Bioavailability
- Fraction of drug reaching systemic circulation unchanged after a specific route of administration.
- (Amount of drug administered/ amount of drug reaching systemic circulation) * 100
- IV administration gives 100% bioavailability
- First-pass effect: hepatic metabolism of drug when it's absorbed from the gut and delivered to the liver via portal circulation.
- The stronger the first pass effect, the less amount of drug that will be in systemic circulation.
Pharmacokinetics (Absorption) (Bioavailability)
- Bioavailability depends on:
- The amount of drug absorbed from a given dosage form that reaches systemic circulation
- First-pass effect: affected by hepatic metabolism when a drug is absorbed from the gut, and delivered to the liver via the portal circulation..
- The greater the first pass Effect, the lower the bioavailability.
- The amount of drug absorbed from a given dosage form that reaches systemic circulation
Concentration Level, Rate of Absorption
- Not only the magnitude, but also the rate of absorption, is crucial for therapeutic success.
Medicine Administration
- Different administration routes (e.g., inhaled, oral, intravenous, intramuscular, topical, rectal).
Pharmacokinetics (Distribution)
- Distribution: Movement of drugs to the sites of action through blood vessels, from the administration site after absorption.
- Factors Affecting Distribution:
- Blood flow
- Capillary permeability
- Blood brain barrier
- Placental barrier
- Drug structure
- Binding to plasma proteins & tissue proteins
- Affinity to certain organs
- Factors Affecting Distribution:
Capillary Permeability
- Endothelial cells in tissues other than the brain have wide slit junctions allowing easy drug movement.
- Brain capillaries have tight junctions, thus drugs must be lipophilic or carrier-mediated to enter the CNS.
Volume of Distribution
- Relates the amount of drug in the body to the drug's blood/plasma concentration.
- Helps determine the loading dose needed to reach the target plasma concentration.
- Vd= Amount of drug in the body/ Plasma Concentration.
- Loading dose = Vd x C (plasma concentration)
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Description
Test your knowledge on the fundamental concepts of pharmacokinetics. This quiz covers topics such as drug absorption, bioavailability, drug movement mechanisms, and the characteristics that affect a drug's efficacy. Challenge yourself to understand how drugs interact within the body!
