Pharmacodynamics Flashcards
What drug does to the body (25 cards)
Different types of drug receptors
- Ligand-gated ion channels - time scale: ms
eg Nicotinic and ACh receptor - G protein-coupled receptors - time scale: secs
eg Muscarinic and Ash receptor - Kinase-linked receptors - time scale: Hours
eg Cytokine receptors - Nuclear receptors - time scale: hours
eg oestrogen receptors
Analyse drug-receptor binding. What determines strong and weak bonds
- Non-covalent bonds (Weak forces)
- Reversible
- Diminish over distance hence drug delivery to site is important - Covalent bonds (High bond energy)
- Irreversible
Concentration-response relationship EC50
EC50 - Concentration required to produce 50% of Max response
Linear phase - small change in serum conc can cause large change
Saturable phase - more conc causes small to no changes in pharmacologic effect
Potency
Amount of drug required for a given level of effect
higher potency = lower dose required
(Look at graph based on Log D of x-axis and also EC50)
Efficacy
Ability of drug to produce MAX response
Higher the efficacy, able to achieve max response
Lethal Dose vs Toxic dose
LD50 - Lethal dose needed to kill 50% population
TD50 - Toxic dose needed to produce 50% of toxic effects
Median Effect dose ED50
Median Effect dose that respond to 50% of population
Therapeutic Index (TI)
Risk benefit ratio calculated which is the margin of safety of a drug. Measured between ED50 and TD50
Larger TI - safer drug
Narrow TI - small changes can result in unwanted toxicity or under treatment - require closer/frequent monitoring of serum levels
Which of the following best defines potency?
A. The maximal effect a drug can produce
B. The dose required to produce a given effect
C. The binding affinity of the drug
D. The variability of drug response
B
- Potency is the dose required to elicit a response.
The therapeutic index is defined as:
A. ED50/LD50
B. LD50/ED50
C. TD50/ED50
D
ED50/TD50
B
- TI = LD50/ED50 – higher ratio = safer drug.
Which of the following statements about competitive antagonists is true?
A. They decrease the maximal response of an agonist
B. They increase the efficacy of an agonist
C. Their effects can be overcome by increasing the dose of the agonist
D. They form irreversible bonds with receptors
C
- Competitive antagonists’ effects can be reversed by increasing agonist.
Desensitization of receptors due to continuous exposure to a drug is referred to as:
A. Tolerance
B Tachyphylaxis
C. Sensitization
D. Dependence
B
- Tachyphylaxis = rapid desensitization. Tolerance is slower, needing dose escalation over time
An inverse agonist differs from an antagonist in that it:
A. Blocks receptor activity without activating it
B. Produces the opposite effect of an agonist
C. Enhances the effect of the agonist
D. Competes with the agonist at the allosteric site
B
- Inverse agonists bind to active receptors and produce opposite effects. Antagonists block but don’t activate or inhibit
Which of the following statements about partial agonists is correct?
A. They produce a maximal response at low concentrations
B. They have higher efficacy than full agonists
C. They produce a submaximal response even when fully occupying receptors
D. They can never act as antagonists
C
- Partial agonists produce less than maximum response, even at full receptor occupancy.
What is the clinical significance of a drug having a narrow therapeutic index? Provide examples.
A narrow therapeutic index means the difference between therapeutic and toxic concentrations is small. Even minor dose changes or drug interactions can cause toxicity or treatment failure. For example, Warfarin requires frequent INR monitoring to avoid bleeding risk. Vancomycin levels are monitored to ensure efficacy while preventing nephrotoxicity.
Explain the concept of receptor upregulation and downregulation with examples.
Upregulation occurs when receptors increase in number due to chronic inhibition (e.g., sudden withdrawal of beta-blockers → rebound hypertension).
Downregulation occurs with prolonged stimulation, leading to reduced receptor numbers (e.g., tolerance in chronic opioid use).
Define and differentiate between efficacy and potency.
Potency refers to the amount of drug needed to produce an effect; a more potent drug achieves the same effect at a lower dose.
Efficacy is the maximal response a drug can produce. A drug may be more potent but less efficacious, or vice versa.
Which of the following is a type of medication-receptor protein that is located in cytoplasm and includes thyroid and steroid hormone receptors?
A. G-protein—coupled receptors
B. Multisubunit ion channels
C. Protein kinases
D. Transcription factors
D
- Transcription factors. Transcription factors are located in cytoplasm; vitamin D and steroid and thyroid hormones are examples.
Choices A, B, and C: G-protein—coupled receptors, multisubunit ion channels, and protein kinases are located in the cell surface transmembrane.
Receptor upregulation and downregulation affect which dimension of medication functioning?
A. Adaptation to medications
B. Contraction
C. Medication association and dissociation from the target
D. Receptor-coupling
A
- Adaptation to medications. Receptor upregulation and downregulation affect adaptation to medications (eg, desensitization, tachyphylaxis, tolerance, acquired resistance, postwithdrawal supersensitivity).
Which of the following is an example of competitive antagonism?
A. Adrenaline vs histamine
B. Benzodiazepine vs histamine
C. Naloxone vs morphine
D. A proton pump inhibitor vs an H2 blocker
C
- Naloxone vs morphine. Naloxone (an opioid receptor antagonist that is structurally similar to morphine), when given shortly before or after morphine, blocks morphine’s effects. However, competitive antagonism by naloxone can be overcome by giving more morphine.
Pharmacodynamics is best described as the study of which of the following?
A. Variations in medication response due to genetic makeup
B. What a medication does to the body
C. What the body does to the medication
D. Which medications treat which diseases
B
- What a medication does to the body. This defines the study of pharmacodynamics. Choice A describes the study of pharmacogenetics, choice C describes pharmacokinetics, and choice D describes pharmacotherapy.
Pharmacodynamics, along with which of the following specific fields of study, helps explain the relationship between the dose and response (ie, the effects) of a medication?
A. Pharmacogenetics
B. Pharmacokinetics
C. Pharmacotherapy
D. Pharmacovigilance
B
- Pharmacokinetics. The study of pharmacokinetics along with pharmacodynamics helps explain the relationship between the dose and response of a medication within the body. Choices A, C, and D are incorrect.
A medication’s pharmacodynamics can be affected by physiologic changes due to which of the following?
A. A disorder or disease
B. Aging process
C. Other medications
D. All of the above
D
- All of the above. Physiologic changes due to all three of these choices can affect a medication’s pharmacodynamics.
Which of the following is a feature of drug resistance?
A. Induction of cytochrome P-450 enzymes occurs.
B. Microorganisms are no longer inhibited by a previously effective drug.
C. Response to a drug that is used repeatedly decreases.
D. Drugs involved include alcohol and opioids.
B
- Microorganisms are no longer killed or inhibited by a previously effective drug.
A: One mechanism responsible for tolerance is accelerated metabolism, for example, by induction of hepatic enzymes such as the cytochrome P-450 system enzymes.
C: Drug tolerance is a decrease in response to a drug that is used repeatedly.
D: Drugs that result in tolerance include alcohol and opioids.
