Skip to contentMCQ on Mechanism of Drug Action and Pharmacodynamics
🟢 Easy Level (1–20)
- Pharmacodynamics is the study of:
a) What the drug does to the body ✔️
b) What the body does to the drug
c) Drug absorption
d) Drug metabolism
Explanation: Pharmacodynamics focuses on drug effects and mechanisms. - The main site of drug action is the:
a) Liver
b) Receptor ✔️
c) Kidney
d) Intestine
Explanation: Drugs usually act by binding to receptors. - An agonist is a substance that:
a) Blocks a receptor
b) Activates a receptor ✔️
c) Destroys a receptor
d) Has no action
Explanation: Agonists mimic the effect of endogenous substances. - An antagonist:
a) Stimulates a receptor
b) Blocks receptor activity ✔️
c) Enhances metabolism
d) Is an enzyme
Explanation: Antagonists prevent the action of agonists. - Drug-receptor binding follows:
a) Linear kinetics
b) Lock-and-key model ✔️
c) Random chance
d) Osmotic flow
Explanation: Specificity and affinity define this interaction. - Potency refers to:
a) Maximum effect
b) Dose required to produce an effect ✔️
c) Duration of action
d) Half-life
Explanation: Lower dose = higher potency. - Efficacy refers to:
a) Maximum effect a drug can produce ✔️
b) Dose of drug
c) Speed of onset
d) Absorption rate
Explanation: High efficacy = greater therapeutic effect. - EC50 is the concentration at which:
a) 50% of maximal effect is achieved ✔️
b) Drug is eliminated
c) Receptors are saturated
d) Toxicity appears
Explanation: It’s used to measure drug potency. - Which of the following is an example of a receptor?
a) DNA
b) Beta-adrenergic receptor ✔️
c) Plasma
d) Ribosome
Explanation: Receptors are proteins that drugs target. - A partial agonist:
a) Fully activates receptor
b) Produces sub-maximal response ✔️
c) Blocks receptor
d) Is inactive
Explanation: It binds but produces less than full effect. - Which is a type of drug action?
a) Radiation
b) Enzyme inhibition ✔️
c) X-ray scattering
d) Hemolysis
Explanation: Drugs can inhibit enzymes to produce effects. - The therapeutic index (TI) is:
a) Ratio of toxic dose to effective dose ✔️
b) A potency scale
c) Drug half-life
d) Duration of therapy
Explanation: TI indicates drug safety margin. - Tachyphylaxis refers to:
a) Rapid decrease in drug response ✔️
b) Steady effect
c) Drug accumulation
d) Tolerance
Explanation: Repeated doses lead to reduced effect. - Tolerance is:
a) Hypersensitivity
b) Reduced response after repeated use ✔️
c) Toxicity
d) First-pass metabolism
Explanation: More drug needed over time to achieve effect. - Inverse agonist:
a) Has no effect
b) Produces opposite effect to agonist ✔️
c) Blocks receptor
d) Enhances agonist
Explanation: It reduces basal receptor activity. - Which of the following interacts with DNA?
a) Beta-blockers
b) Anticancer drugs ✔️
c) Antacids
d) Antihistamines
Explanation: Many chemotherapeutic agents bind DNA. - Non-specific drug actions include:
a) Receptor binding
b) Changing pH ✔️
c) Enzyme activation
d) G-protein stimulation
Explanation: Antacids and osmotic diuretics act non-specifically. - Dose-response curve plots:
a) Time vs. concentration
b) Dose vs. effect ✔️
c) Effect vs. toxicity
d) Receptor vs. DNA
Explanation: It visualizes the drug’s effect range. - Allosteric modulators bind to:
a) Active site
b) Alternate site ✔️
c) DNA
d) Blood proteins
Explanation: They enhance or reduce receptor activity. - A competitive antagonist:
a) Competes with agonist for receptor ✔️
b) Binds irreversibly
c) Enhances effect
d) Activates G-proteins
Explanation: Can be overcome with higher agonist concentration.
🟡 Moderate Level (21–40)
- Non-competitive antagonists:
a) Compete for active site
b) Bind irreversibly to receptor ✔️
c) Increase potency
d) Act as prodrugs
Explanation: Their effect cannot be reversed by agonist. - Drugs acting through ion channels:
a) Alter membrane permeability ✔️
b) Bind to DNA
c) Change protein synthesis
d) Inhibit blood cells
Explanation: Ion channels regulate ion flow, affecting cell function. - Second messengers include:
a) DNA and RNA
b) cAMP and IP3 ✔️
c) Na+ and Cl-
d) Glucose and lipids
Explanation: They mediate intracellular effects of drugs. - G-protein-coupled receptors (GPCRs) involve:
a) Direct DNA binding
b) Activation of intracellular signaling ✔️
c) Plasma degradation
d) Albumin synthesis
Explanation: GPCRs trigger signal cascades. - Drug selectivity means:
a) Drug acts on specific receptor ✔️
b) Drug binds all tissues
c) Drug shows no effect
d) All receptors are activated
Explanation: Selectivity reduces side effects. - Intrinsic activity of an agonist is:
a) Zero
b) 1 ✔️
c) -1
d) 0.5
Explanation: Full agonists have intrinsic activity = 1. - Irreversible antagonists:
a) Permanently block receptors ✔️
b) Require lower doses
c) Dissociate easily
d) Increase receptor number
Explanation: Covalent or strong binding makes it irreversible. - Drug action at enzyme level may involve:
a) DNA synthesis
b) Enzyme inhibition ✔️
c) ATP storage
d) O2 transport
Explanation: Common in antimicrobials. - Tolerance due to enzyme induction is:
a) Pharmacokinetic ✔️
b) Pharmacodynamic
c) Receptor mutation
d) Genetic
Explanation: Body increases metabolism capacity. - The ceiling effect relates to:
a) Increased toxicity
b) Maximal effect of a drug ✔️
c) Minimum dose
d) Time to onset
Explanation: Dose beyond which no effect increases. - Drug with low therapeutic index:
a) Very safe
b) Requires close monitoring ✔️
c) Highly selective
d) Short-acting
Explanation: Narrow margin between therapeutic and toxic dose. - Receptor downregulation leads to:
a) Hypersensitivity
b) Decreased response ✔️
c) Faster metabolism
d) Enhanced effect
Explanation: Fewer receptors reduce response. - Which is a nuclear receptor?
a) Beta-2 receptor
b) Estrogen receptor ✔️
c) Histamine receptor
d) Muscarinic receptor
Explanation: Steroid hormones act via nuclear receptors. - Placebo effect is:
a) No effect
b) Psychological benefit from inert substance ✔️
c) Drug side effect
d) Enzyme inhibition
Explanation: Belief causes perceived improvement. - The therapeutic window is:
a) Cost-effective range
b) Range between effective and toxic dose ✔️
c) Storage temperature
d) Drug purity
Explanation: Safe and effective dosing range. - GPCRs have how many transmembrane segments?
a) 4
b) 9
c) 7 ✔️
d) 10
Explanation: It’s a hallmark of this receptor class. - Biased agonism refers to:
a) Incorrect drug use
b) Selective pathway activation ✔️
c) Antagonism
d) Tolerance
Explanation: Activates only certain receptor functions. - Desensitization occurs due to:
a) Drug degradation
b) Liver failure
c) Receptor internalization ✔️
d) Overdosing
Explanation: Receptors become less responsive. - Which drug acts through enzyme induction?
a) Digoxin
b) Rifampicin ✔️
c) Aspirin
d) Propranolol
Explanation: Rifampicin induces liver enzymes. - Inhibiting acetylcholinesterase leads to:
a) Increased acetylcholine ✔️
b) Muscle paralysis
c) Decreased heart rate
d) DNA damage
Explanation: Acetylcholine is broken down slower.
🔴 Hard Level (41–50)
- Dose-response curve of partial agonist shows:
a) Lower maximum response ✔️
b) No response
c) Steep increase
d) Inverse response
Explanation: It never reaches full effect. - Spare receptors exist when:
a) All receptors are occupied
b) Maximal effect occurs without full receptor occupancy ✔️
c) Receptors are downregulated
d) Potency is low
Explanation: Indicates receptor reserve. - Which receptor is ligand-gated?
a) Insulin receptor
b) Nicotinic acetylcholine receptor ✔️
c) Estrogen receptor
d) GPCR
Explanation: Opens ion channels upon ligand binding. - A sigmoid dose-response curve implies:
a) Graded effect ✔️
b) All-or-none response
c) Fixed potency
d) Constant slope
Explanation: Typical of most drug responses. - ED50 refers to:
a) Effective dose for 50% population ✔️
b) Toxic dose
c) Minimum dose
d) Bioavailability
Explanation: Used to measure drug effectiveness. - Inverse agonists act on:
a) Constitutively active receptors ✔️
b) Non-functional receptors
c) Non-competitive sites
d) G-proteins directly
Explanation: They reduce basal receptor activity. - G-proteins act as:
a) Molecular switches ✔️
b) DNA replicators
c) Enzymes
d) Hormones
Explanation: Activate or inhibit intracellular pathways. - A high-affinity drug:
a) Binds strongly to its receptor ✔️
b) Is non-specific
c) Is toxic
d) Is hydrophilic
Explanation: Needs lower concentrations to bind. - A low KD (dissociation constant) means:
a) High affinity ✔️
b) Low efficacy
c) Poor selectivity
d) Fast clearance
Explanation: KD is inversely related to affinity. - Signal transduction starts with:
a) Enzyme action
b) Ligand-receptor binding ✔️
c) DNA binding
d) Protein breakdown
Explanation: First step in cellular response.
