Drug Efficacy and Potency — MCQs
The therapeutic index of a drug is defined as the ratio between the toxic dose and the effective dose.
Which of the following statements is correct regarding the given graph?
Which of the following best demonstrates the variability in drug responsiveness among individuals?
Therapeutic index of a drug is an indicator of:-
Which of the following statement is correct regarding the given DRC? (AllMS Nov 2016)
A 70 kg man was given a drug with a dose of 100 mg/kg body weight, twice daily. The half-life (t1/2) is 10 hours, the plasma concentration is 1.9 mg/mL, and the clearance is unknown. What is the clearance of this drug?
The graph below shows dose-response curves for three drugs A, B, and C. Which of the following drugs has the highest potency?
What is the shelf life of Dukoral (wc-rBS) oral vaccine used for cholera prevention, when stored at a temperature of 2 °C to 8 °C?
Which drug is metabolized by glutathionation?
What do A and B represent in the curve shown below?
Drug Efficacy and Potency Indian Medical PG Practice Questions and MCQs
Question 1: The therapeutic index of a drug is defined as the ratio between the toxic dose and the effective dose.
- A. Margin of safety
- B. Ratio of toxic dose to effective dose (Correct Answer)
- C. Efficacy of the drug
- D. Drug potency
Explanation: ***Ratio of toxic dose to effective dose***- The **therapeutic index (TI)** is quantitatively defined as the ratio of the toxic dose (TD50 or LD50) to the effective dose (ED50) [1, 2].- This ratio provides a measure of **drug safety**, indicating the range between the therapeutic and toxic concentrations [1, 3].*Margin of safety*- While related to safety, the **margin of safety** is a different concept, often calculated as (TD1 - ED99) / ED99, focusing on the overlap between very few people experiencing toxicity and almost everyone receiving benefit [2].- The therapeutic index is a broader, simpler ratio that doesn't explicitly guarantee overlap safety but indicates overall drug risk.*Efficacy of the drug*- **Efficacy** refers to the maximal effect a drug can produce regardless of the dose, and it is independent of the therapeutic index [2].- A drug can have high efficacy but a narrow therapeutic index, meaning it is very effective but also very toxic at doses slightly above the therapeutic range.*Drug potency*- **Potency** is the amount of drug needed to produce a given effect (e.g., ED50), reflecting its affinity for receptors and efficiency of action [2].- It is distinct from the therapeutic index, which assesses the separation between desired and undesired effects, not the concentration required to achieve a therapeutic effect.
Question 2: Which of the following statements is correct regarding the given graph?
- A. Drug 1 represents agonist and drug 2 represents inverse agonist
- B. Drug 3 represents agonist and drug 4 represents inverse agonist
- C. Drug 2 represents partial agonist and drug 3 represents inverse agonist
- D. Drug 1 represents agonist and drug 4 represents inverse agonist (Correct Answer)
Explanation: ***Drug 1 represents agonist and drug 4 represent inverse agonist*** - **Drug 1** demonstrates maximal efficacy, producing a **supraphysiologic response** above the baseline (100%), characteristic of an **agonist**. - **Drug 4** produces a response **below the baseline** (100%), indicating inhibition of constitutive receptor activity, which is the definition of an **inverse agonist**. *Drug 1 represents agonist and drug 2 represents inverse agonist* - While **Drug 1** is correctly identified as an **agonist** due to its maximal effect above baseline, **Drug 2** is a **partial agonist**, as it produces a submaximal effect above baseline but does not reach the full agonist's efficacy. - **Drug 2** does not reduce the baseline response, so it cannot be an inverse agonist. *Drug 3 represents agonist and drug 4 represents inverse agonist* - **Drug 3** maintains the **baseline response** (at 100%) regardless of concentration, indicating it is a **neutral antagonist** or has no effect, not an agonist. - **Drug 4** is correctly identified as an **inverse agonist** because it reduces the baseline receptor activity. *Drug 2 represents partial agonist and drug 3 represents inverse agonist* - **Drug 2** is correctly identified as a **partial agonist** as it produces an effect above baseline but less than a full agonist. - **Drug 3** is incorrect; it shows no change from baseline (100%), reflecting a **neutral antagonist** or inactive substance, not an inverse agonist which would decrease the baseline response.
Question 3: Which of the following best demonstrates the variability in drug responsiveness among individuals?
- A. Potency
- B. Quantal Dose Response Curve (Correct Answer)
- C. Efficacy
- D. Graded Dose Response Curve
Explanation: ***Quantal Dose Response Curve*** - A **quantal dose-response curve** plots the percentage of individuals exhibiting a discrete, all-or-none effect against the log dose of a drug. - This curve directly illustrates the **variability in drug responsiveness** within a population by showing the range of doses required to produce a specific effect in different individuals. *Efficacy* - **Efficacy** refers to the maximum effect a drug can produce, regardless of the dose. - While efficacy is an important pharmacological parameter, it describes the drug's overall therapeutic potential, not the **individual variability** in response. *Potency* - **Potency** is a measure of the amount of drug needed to produce an effect of given intensity. - It relates to the absolute dose required for a particular effect but does not directly demonstrate the **inter-individual differences** in biological response. *Graded Dose Response Curve* - A **graded dose-response curve** depicts the relationship between the dose of a drug and the **magnitude of the effect** in a **single biological unit** (e.g., an individual, a tissue, or a cell). - This curve reflects the relationship between drug concentration and effect intensity, but not the **variability in response among different individuals** in a population.
Question 4: Therapeutic index of a drug is an indicator of:-
- A. All of these
- B. Potency
- C. Safety (Correct Answer)
- D. Efficacy
Explanation: ***Safety*** - The **therapeutic index (TI)** is a ratio comparing the **toxic dose (TD50)** to the **effective dose (ED50)**: TI = TD50/ED50. - It indicates the **margin of safety** of a drug—the wider the margin between therapeutic and toxic doses, the safer the drug. - A **high therapeutic index** means greater safety; a **low therapeutic index** means the drug has a narrow safety margin. *Potency* - **Potency** refers to the amount of drug needed to produce a given effect, represented by the **ED50**. - The therapeutic index is a **ratio**, not a measure of potency alone. - A highly potent drug can still have a narrow therapeutic index if its toxic dose is close to its effective dose. *Efficacy* - **Efficacy** describes the **maximum therapeutic effect** a drug can produce, irrespective of dose. - The therapeutic index does not quantify maximum effect but rather the **safety margin** within which therapeutic effects can be achieved. *All of these* - While potency and efficacy are important drug properties, the therapeutic index **specifically indicates safety**. - TI is not a composite measure of all drug properties—it is exclusively a safety parameter.
Question 5: Which of the following statement is correct regarding the given DRC? (AllMS Nov 2016)
- A. C is non-competitive antagonist
- B. B is more potent than A
- C. A is more efficacious than B
- D. A and B are full agonists (Correct Answer)
Explanation: ***A and B are full agonists*** - Both Drug A and Drug B reach the **maximum biological effect**, indicated as 100 on the y-axis, meaning they are capable of producing the full response. - A full agonist is a substance that binds to a receptor and produces the **maximum possible biological response**. *C is non-competitive antagonist* - Drug C *does* produce a biological effect, albeit a lower one, making it a **partial agonist**, not an antagonist. - A non-competitive antagonist would **reduce the maximum effect** of the agonist and shift the curve downwards, which is not what is observed here for C. *B is more potent than A* - Drug A achieves 50% of its maximal effect at a **lower concentration** than Drug B (i.e., further to the left on the x-axis). - Therefore, Drug A is **more potent** than Drug B, as potency is inversely related to the concentration required for a given effect. *A is more efficacious than B* - Both Drug A and Drug B reach the **same maximum biological effect** (100 on the y-axis), indicating they have equal efficacy. - Efficacy refers to the **maximum effect** a drug can produce, regardless of the dose.
Question 6: A 70 kg man was given a drug with a dose of 100 mg/kg body weight, twice daily. The half-life (t1/2) is 10 hours, the plasma concentration is 1.9 mg/mL, and the clearance is unknown. What is the clearance of this drug?
- A. 20 liter/hr
- B. K is 0.0693
- C. 0.22 L/hr (Correct Answer)
- D. 0.02 L/hr
Explanation: ***0.22 L/hr*** - To calculate clearance at steady state, we use the formula: **Clearance (Cl) = Dose Rate / Css** (steady-state plasma concentration). - **Dose rate calculation**: 100 mg/kg × 70 kg × 2 doses/day = 14,000 mg/day = 583.33 mg/hr - **Converting plasma concentration**: 1.9 mg/mL = 1900 mg/L - **Clearance calculation**: Cl = 583.33 mg/hr ÷ 1900 mg/L = **0.307 L/hr** - **Note**: The calculated value (0.307 L/hr) does not exactly match any option. The marked answer (0.22 L/hr) is the closest approximation among the given choices. This discrepancy may arise from rounding in the original question parameters or implicit assumptions about bioavailability/volume of distribution. *0.02 L/hr* - This value is approximately 15 times lower than the calculated clearance. - Such low clearance would result in much higher plasma concentrations or require significantly lower dosing. *20 liter/hr* - This clearance is approximately 65 times higher than calculated, representing an unrealistically high value for this scenario. - Such high clearance would result in very low plasma concentrations unless extremely high doses were administered. *K is 0.0693* - This represents the **elimination rate constant (k)**, calculated as k = 0.693/t1/2 = 0.693/10 hr = 0.0693 hr⁻¹. - While mathematically correct for k, the question specifically asks for **clearance**, not the elimination rate constant. - Clearance is related to k by: Cl = k × Vd (volume of distribution).
Question 7: The graph below shows dose-response curves for three drugs A, B, and C. Which of the following drugs has the highest potency?
- A. Drug A (Correct Answer)
- B. Drug B
- C. Drug C
- D. Both Drug A & B
Explanation: ***Drug A*** - Potency is inversely related to the **concentration required to produce an effect (EC50)**. A lower EC50 indicates higher potency. - Drug A achieves its half-maximal effect (indicated by the dashed line) at approximately **0.01 concentration**, which is the lowest among all three drugs. *Drug B* - Drug B reaches its half-maximal effect at a concentration of approximately **1**, which is significantly higher than Drug A. - This indicates that a larger dose of Drug B is needed to achieve the same effect as Drug A, making it less potent than A. *Drug C* - Drug C requires the highest concentration, approximately **100**, to achieve its half-maximal effect. - This signifies that Drug C is the least potent among the three drugs, as it demands a much larger dose for an equivalent effect compared to A and B. *Both Drug A & B* - While Drug A is highly potent, Drug B is less potent as it requires a higher concentration to elicit its effect. - Therefore, it is incorrect to state that both drugs A and B have the highest potency.
Question 8: What is the shelf life of Dukoral (wc-rBS) oral vaccine used for cholera prevention, when stored at a temperature of 2 °C to 8 °C?
- A. 2 years (Correct Answer)
- B. 3 years
- C. 6 months
- D. 5 years
Explanation: ***2 years***- Dukoral (wc-rBS) oral vaccine, when stored correctly at **2 °C to 8 °C**, maintains its efficacy and stability for **2 years**. - This is the manufacturer-specified shelf life that ensures the vaccine remains potent and safe for use. - The vaccine contains inactivated whole-cell V. cholerae and recombinant cholera toxin B subunit, with a validated 2-year stability period. *3 years*- A 3-year shelf life is an **overestimation** for Dukoral under standard refrigerated storage conditions. - Beyond the validated 2-year period, the vaccine's potency cannot be guaranteed. - This could lead to administration of potentially ineffective vaccine. *6 months*- A 6-month shelf life is significantly **underestimated** for Dukoral, indicating a lack of understanding of vaccine stability. - Such a short duration would lead to premature discarding of usable vaccine and increased waste. - Most modern refrigerated vaccines have longer shelf lives than this. *5 years*- A 5-year shelf life is a significant **overestimation** for Dukoral (wc-rBS). - This duration exceeds the manufacturer's validated stability data for this oral vaccine. - Using vaccine beyond its validated shelf life poses risks of reduced immunogenicity.
Question 9: Which drug is metabolized by glutathionation?
- A. Nicotinic acid
- B. Fosfomycin
- C. Benzodiazepines
- D. Dapsone (Correct Answer)
Explanation: ***Dapsone***- **Dapsone** undergoes hepatic metabolism via **N-hydroxylation** by CYP450 enzymes (particularly CYP2E1 and CYP3A4), forming reactive **hydroxylamine metabolites**.- These reactive metabolites are toxic and can cause **methemoglobinemia** and **hemolysis**.- **Glutathione conjugation (glutathionation)** serves as an important **detoxification pathway** for these reactive dapsone metabolites [1].- Individuals with **glutathione deficiency** (such as G6PD deficiency) are at increased risk of dapsone-induced hemolytic anemia [2].*Fosfomycin*- **Fosfomycin** is primarily eliminated by the kidneys as an **unchanged drug** (up to 90% excreted unchanged in urine).- It undergoes **minimal hepatic metabolism** and does NOT undergo significant glutathionation.- Its primary route of elimination is **renal excretion** via glomerular filtration.*Benzodiazepines*- **Benzodiazepines** are primarily metabolized in the liver via **CYP450 enzymes** (Phase I oxidation) followed by **glucuronidation** (Phase II conjugation).- They do NOT undergo glutathionation as a significant metabolic pathway.*Nicotinic acid*- **Nicotinic acid** (niacin) undergoes conjugation with **glycine** to form nicotinuric acid and **methylation** to form N-methylnicotinamide.- It does NOT undergo glutathione conjugation.
Question 10: What do A and B represent in the curve shown below?
- A. A= Median effective dose, B= Median lethal dose (Correct Answer)
- B. A= Therapeutic index, B= Median efficacy
- C. A= Median lethal dose, B= Median effective dose
- D. A= Median efficacy, B= Therapeutic index
Explanation: ***A= Median effective dose, B= Median lethal dose*** - **A** corresponds to the **median effective dose (ED50)**, which is the dose that produces a therapeutic effect in 50% of the population - The purple curve represents the dose-response for efficacy; at A, 50% of individuals are responding effectively - **B** corresponds to the **median lethal dose (LD50)**, which is the dose that is lethal to 50% of the population - The red curve represents the dose-response for toxicity/lethality; at B, 50% of individuals are experiencing a lethal outcome *A= Therapeutic index, B= Median efficacy* - The **therapeutic index** is a ratio (LD50/ED50), not a specific dose represented on the x-axis - **Median efficacy** is not a standard pharmacological term to represent a point on a dose-response curve; rather, efficacy refers to the maximal effect a drug can produce *A= Median lethal dose, B= Median effective dose* - This option reverses the correct identification of A and B - **Median effective dose (ED50)** is typically expected at lower doses, while **median lethal dose (LD50)** is at higher doses, indicating toxicity - In the provided graph, the curve for A occurs at a much lower dose range than the curve for B, making it the effective dose, not the lethal dose *A= Median efficacy, B= Therapeutic index* - **Median efficacy** is not a specific dose value represented this way on a dose-response curve - The **therapeutic index** is a ratio, not a dose point on the graph
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