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Questions and Answers
What is pharmacodynamics the study of?
What is pharmacodynamics the study of?
Define the term 'agonist' in drug-receptor interactions.
Define the term 'agonist' in drug-receptor interactions.
An agonist is a drug that binds to a receptor and results in the activation of a receptor response.
The attraction between a receptor and a ligand is known as __________.
The attraction between a receptor and a ligand is known as __________.
affinity
Non-competitivity in drug-receptor interactions is reversible.
Non-competitivity in drug-receptor interactions is reversible.
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What are the main processes involved in pharmacokinetics?
What are the main processes involved in pharmacokinetics?
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What is the goal of drug metabolism in the body?
What is the goal of drug metabolism in the body?
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Simple diffusion is the most common mechanism for drug transport across biological barriers.
Simple diffusion is the most common mechanism for drug transport across biological barriers.
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Vitamin C is transported across cell membranes by ________.
Vitamin C is transported across cell membranes by ________.
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Match the factors affecting drug absorption with their descriptions:
Match the factors affecting drug absorption with their descriptions:
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What is the definition of half-life of a drug?
What is the definition of half-life of a drug?
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What determines the half-life of a drug primarily?
What determines the half-life of a drug primarily?
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A drug is given at a dose of 500 mg. If it takes 4 hours to decrease its concentration to 250 mg, how long will it take for the drug to go through 3 half-life periods?
A drug is given at a dose of 500 mg. If it takes 4 hours to decrease its concentration to 250 mg, how long will it take for the drug to go through 3 half-life periods?
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What percentage of a drug is remaining after 3 half-life periods?
What percentage of a drug is remaining after 3 half-life periods?
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What is the common major organ for drug metabolism?
What is the common major organ for drug metabolism?
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Which enzyme plays a significant role in drug metabolism?
Which enzyme plays a significant role in drug metabolism?
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The blood-brain barrier allows all drugs to freely enter the brain.
The blood-brain barrier allows all drugs to freely enter the brain.
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Drug distribution is determined by its lipid solubility and the pH gradient between the intracellular and extracellular fluids, as well as factors like ________________.
Drug distribution is determined by its lipid solubility and the pH gradient between the intracellular and extracellular fluids, as well as factors like ________________.
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Match the following drug administration routes with their descriptions:
Match the following drug administration routes with their descriptions:
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Study Notes
Pharmacodynamics
- Pharmacodynamics is the study of drug action and investigates the mechanisms by which a drug elicits a pharmacologic response.
- Drugs produce their effects by binding to receptors, either stimulating or inhibiting these sites.
- There are two main ways drugs bind to receptors:
- Binding to the endogenous ligand recognition site
- Binding to an allosteric site on the receptor molecule
Drug-Receptor Interactions
- Receptors are cellular proteins that bind a transmitter, hormone, or drug and transmit a signal or alter cellular activity.
- The receptor domain to which the ligand binds is known as the recognition site.
- The attraction between a receptor and a ligand is known as the affinity.
- A drug that binds to a receptor and results in the activation of a receptor response is called an agonist.
- A drug that binds to a receptor and prevents its activation by another ligand is called an antagonist.
- Agonists produce maximum activation of the receptor and elicit a maximum response from the tissue.
- Antagonists bind but produce no activation of the receptor and therefore block responses from the tissue.
Intrinsic Activity and Potency
- The intrinsic activity of a drug is the relative maximal response to that agent in a particular experimental model.
- A full agonist causes a maximal response in a particular system.
- A partial agonist is unable to induce a maximal response, even at high concentrations.
- Potency is a property that is frequently used to compare different drugs.
- The more potent the drug, the fewer the number of molecules required to produce a desired effect.
- EC50 is the parameter used to evaluate differences in drug potency.
Forms of Antagonism
- Competitive antagonism occurs when a drug binds without activating its receptor and thereby prevents activation by an agonist.
- Increasing agonist concentration can overcome the binding of a competitive antagonist.
- Non-competitive antagonism occurs when the bonds between the drug and the receptor are strong.
- Increasing agonist concentration cannot overcome the binding of a non-competitive antagonist.
- Functional (physiological) antagonism occurs when two agonists acting via different receptors affect the same variable in opposite directions.
- Chemical antagonism occurs when a chemical antagonist interacts directly with the drug being antagonized to remove it or to prevent it from binding to its target.
Therapeutic Index
- The therapeutic index (TI) is a measurement of drug safety.
- TI refers to the relationship between toxic and therapeutic dosing.
- TI = TD50/ED50
- Drugs with a narrow therapeutic window (e.g. theophylline, warfarin, valproate, lithium) have a higher risk of toxicity.
- Drugs with a wide therapeutic window (e.g. most antibiotics) have a lower risk of toxicity.
Introduction to Pharmacology
- Pharmacology is the science of drugs and their interactions with living systems.
- Drugs are used for diagnosis, prevention, and treatment of diseases.
- Drugs can be derived from various sources.
Pharmacokinetics
- Pharmacokinetics is the study of what the body does to the medication.
- It involves the processes of absorption, distribution, metabolism, and excretion.
Absorption
- Absorption is the passage of a drug from the site of administration to the circulation.
- Transportation mechanisms:
- Simple (passive) diffusion
- Active transport
- Facilitated diffusion
- Pinocytosis
- Factors affecting absorption:
- Solubility
- Ionization degree
- pH of the environment
- Surface area
- Contact time at the absorption site
- Concentration of the drug at the administered site
- Molecular weight
- Type of drug formulation
- Blood flow
- Drug interactions affecting absorbance
- Gastric emptying time
Bioavailability and First-Pass Metabolism
- Bioavailability is the relative amount of the administered drug that reaches the systemic circulation in the unchanged form.
- First-pass metabolism is the metabolism of drugs by the liver and intestinal flora before they reach the general circulation.
- Factors affecting bioavailability:
- Solubility
- Chemical stability
- First-pass metabolism in the liver
- Disorders or previous GI surgery
- Whether the drug is taken with or without food
- P-gp transporter
Routes of Drug Administration
- Local routes:
- Topical
- Sublingual
- Rectal
- Systemic routes:
- Enteral (oral, sublingual, rectal)
- Parenteral (intravenous, intramuscular, subcutaneous)
- Other (inhalation, topical, transdermal, rectal)
- Characteristics of administration routes:
- Onset of action
- Bioavailability
- First-pass metabolism
Distribution
- Distribution of a drug in body tissues and fluids.
- Factors affecting distribution:
- Blood flow (perfusion rate)
- Plasma protein binding
- Affinity of the drug to tissue components
- Patterns of distribution:
- Initial rapid phase to highly perfused organs
- Slow phase to muscles, viscera, skin, and fat
Metabolism and Excretion
- Metabolism is the process of converting a drug into its metabolites.
- Factors affecting metabolism:
- Age
- Liver disease
- Genetic differences in levels of CYP450 enzymes
- Inhibition or induction of CYP450 enzymes
- Outcomes of metabolism:
- Inactive metabolites
- Active metabolites (in some cases)
- Excretion is the process of removing a drug and its metabolites from the body.### Inhibition and Induction
- Inhibition: results in a decrease in drug metabolism, decreasing the speed of drug metabolism
- Examples of CYP enzyme inhibitors: grapefruit juice, ketoconazole, and omeprazole
- Inhibition leads to a higher plasma concentration of the drug for a longer time
Factors Affecting Drug Metabolism
- Nutritional status: low protein intake reduces drug clearance by reducing oxidative metabolism
- Metabolism by luminal microflora: changes in the environment of intestinal flora affect drug metabolism
- Disorders or previous GI surgery can affect drug bioavailability
Enzyme Induction and Inhibition
- Induction:
- Occurs slowly over 2-3 weeks
- Increases enzyme synthesis
- Increases metabolism rate
- Decreases duration of drug action
- Decreases plasma concentration of the drug
- Inhibition:
- Occurs rapidly
- Directly inhibits the enzyme
- Decreases metabolism rate
- Increases duration of drug action
- Increases plasma concentration of the drug
Excretion
- Most drugs are excreted by the kidneys and eliminated unchanged or as metabolites in the urine
- Other excretion routes: bile, intestine, lung, or milk in nursing mothers
- Enterohepatic cycle: drugs or metabolites are excreted in bile, reabsorbed from the small intestine, returned to the liver, metabolized, and eventually excreted in urine
Glomerular Filtration and Tubular Secretion
- Glomerular filtration: free drug flows out of the body and into the urine-to-be as part of the glomerular filtrate
- Size of the molecule is the only limiting factor
- Proximal tubular secretion: occurs in the proximal tubules by two energy-requiring active transport systems
- Premature infants and neonates have an incompletely developed tubular secretory mechanism
Factors Affecting Drug Excretion
- Reabsorption
- pH changes in the urine
- Blood flow to the liver and kidney
- Kidney disease
- Age
- Drug interactions
- Breast milk excretion: depends on drug properties and patient properties
Half-Life
- Defined as the time it takes to eliminate 50% of the drug in the plasma
- Determined primarily by the drug's rates of metabolism and excretion
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Description
This quiz covers the study of pharmacodynamics, including the mechanisms of drug action and how drugs bind to receptors to produce a pharmacologic response.
