Pharmacokinetics and Pharmacodynamics — MCQs

Pharmacokinetics and Pharmacodynamics Indian Medical PG Practice Questions and MCQs

Question 361: A new sedative-hypnotic drug is being evaluated in preclinical toxicity studies. The following quantal dose-response curve is obtained showing the hypnotic effect and lethal effect. Calculate the therapeutic index of the drug being tested.

A. 4.5
B. 1.8 (Correct Answer)
C. 2.5
D. 0.56

Explanation: The image shows a **quantal dose-response curve** depicting the percentage of subjects responding to increasing doses for two effects: **hypnosis** (therapeutic effect) and **death** (toxic effect). The **Therapeutic Index (TI)** is calculated as **TI = LD50/ED50**. **Steps to calculate:** 1. **Determine ED50 for Hypnosis** (therapeutic effect): - Locate 50% response on the Y-axis - Trace horizontally to intersect the "Hypnosis" curve - Trace vertically down to the X-axis (log dose) - ED50 ≈ **2.5** on the log dose scale 2. **Determine LD50 for Death** (toxic effect): - Locate 50% response on the Y-axis - Trace horizontally to intersect the "Death" curve - Trace vertically down to the X-axis (log dose) - LD50 ≈ **4.5** on the log dose scale 3. **Calculate Therapeutic Index:** - **TI = LD50 / ED50 = 4.5 / 2.5 = 1.8** ***Correct Option: 1.8*** - This is the correct therapeutic index calculated from the ratio of LD50 to ED50 - A TI of 1.8 indicates a relatively narrow margin of safety between therapeutic and lethal doses - Higher TI values indicate safer drugs *Incorrect Option: 0.56* - This would be the reciprocal calculation (ED50/LD50), which is not how TI is defined - TI is always LD50/ED50, not the reverse *Incorrect Option: 2.5* - This is the ED50 value (effective dose for hypnosis), not the therapeutic index - This represents only one component of the TI calculation *Incorrect Option: 4.5* - This is the LD50 value (lethal dose), not the therapeutic index - This represents only the numerator in the TI calculation

Question 362: Which is correct about the curves shown?

A. A= Graded dose response curve, B= Dose response curve (Correct Answer)
B. A= Dose response curve, B= Graded dose response curve
C. A= Quantal dose response curve, B= Dose response curve
D. A= Dose response curve, B= Quantal dose response curve

Explanation: ***A= Graded dose response curve, B= Dose response curve*** - Curve A, plotting "Response %" against "Dose," shows a **hyperbolic shape**, which is characteristic of a **graded dose-response curve plotted on a linear scale**. - Curve B, plotting "Response %" against "Log dose," displays a **sigmoidal (S-shaped) curve**, which represents a **graded dose-response curve plotted on a logarithmic scale**. - Both curves are actually graded dose-response curves; the distinction is in the **scale of the x-axis** (linear vs logarithmic), which changes the curve's appearance from hyperbolic to sigmoidal. - In pharmacology teaching, the term "dose response curve" is sometimes used colloquially to refer to the **log-scale sigmoidal plot (Curve B)**, which is the most commonly used representation in clinical pharmacology. *A= Dose response curve, B= Graded dose response curve* - This option reverses the identification of the curves. - Curve A's hyperbolic shape on a linear scale is characteristic of the **graded dose-response relationship without log transformation**. - Curve B's sigmoidal shape results from plotting the same graded response on a **logarithmic dose scale**. *A= Quantal dose response curve, B= Dose response curve* - **Quantal dose-response curves** relate the dose to the **proportion of individuals** in a population who exhibit a specified all-or-none effect (e.g., % of patients achieving blood pressure reduction >20 mmHg). - **Neither graph depicts a quantal response**; both show "Response %" which represents the **magnitude of response** (graded effect) in a single biological system, not the frequency of responders in a population. - Curve A's shape is inconsistent with quantal dose-response characteristics. *A= Dose response curve, B= Quantal dose response curve* - This option incorrectly identifies Curve B as a "Quantal dose response curve." - While **quantal dose-response curves** can produce a sigmoidal cumulative frequency distribution, their y-axis represents the **percentage of individuals responding** (all-or-none), not the **percentage of maximum response** in a graded fashion. - Curve B clearly shows a **graded response** (continuous dose-dependent effect), not a quantal response (proportion achieving threshold effect).

Question 363: The following curve shows a graded dose-response curve. Drug A and drug B are bronchodilators. What do drug C and D represent?

A. C = Noncompetitive antagonist, D = Competitive antagonist
B. C = Competitive antagonist, D = Noncompetitive antagonist (Correct Answer)
C. C = Agonist, D = Partial agonist
D. C = Agonist, D = Competitive antagonist

Explanation: ***C = Competitive antagonist, D = Noncompetitive antagonist*** - Curve C, representing a **competitive antagonist**, shifts the dose-response curve of the agonist to the **right** without reducing the maximal effect. This indicates that a higher concentration of the agonist is needed to overcome the antagonist and achieve the same maximal response. - Curve D, representing a **noncompetitive antagonist**, reduces the **maximal effect** of the agonist and does not significantly shift the curve to the right in the same manner as a competitive antagonist would for the full maximal effect of the agonist. The maximal effect is *permanently* reduced even with increasing agonist concentration. *Noncompetitive antagonist, D = Competitive antagonist* - This is incorrect because a **noncompetitive antagonist** reduces the maximal effect, which is depicted by curve D, while a **competitive antagonist** shifts the curve to the right without reducing maximal effect, as seen in curve C. - The roles of C and D are reversed in this option. *C = Agonist, D = Partial agonist* - This is incorrect as C and D are clearly shown to be modulating the effect of "bronchodilators" (A and B), indicating they are likely antagonists affecting the primary drugs, not agonists themselves. - A **partial agonist** would produce a lower maximal effect than a full agonist, but would still show a dose-response curve with an increasing effect, not a flat line limiting the maximal effect like D. *C = Agonist, D = Competitive antagonist* - This is incorrect as C represents a shift in the agonist's curve, typical of a **competitive antagonist**, not an agonist itself. - If C were an agonist, it would have its own dose-response curve showing increasing effect, similar to A and B.

Question 364: 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

Question 365: Brand A of liposomal amphotericin B is of innovator company and brand B is of a generic company. AUC of Brand A is 124 mg.h/L and AUC of brand B is 115 mg.h/L. Which of the following statements is correct?

A. Brand A is bioequivalent to brand B (Correct Answer)
B. Brand A is not bioequivalent to brand B
C. Brand A has higher volume of distribution than brand B
D. Brand B has higher volume of distribution than brand A

Explanation: ***Brand A is bioequivalent to brand B*** - **Bioequivalence** is generally established if the **90% confidence interval** for the ratio of the **AUC** (and Cmax) of the test product (Brand B) to the reference product (Brand A) falls within **80-125%**. - Here, the ratio of AUC (Brand B / Brand A) is 115/124 ≈ 0.927 or 92.7%. This value falls well within the accepted range of 80-125%, indicating bioequivalence. *Brand A is not bioequivalent to brand B* - This statement is incorrect because the AUC ratio (115/124 ≈ 0.927) is within the **standard bioequivalence range of 80-125%**, indicating that the two brands are indeed bioequivalent. - While there are differences in Cmax and Tmax for the two brands as shown in the graph, the provided AUC values suggest bioequivalence for the overall drug exposure. *Brand A has higher volume of distribution than brand B* - The provided **AUC values** (Area Under the Curve) primarily reflect the **extent of drug exposure** and are not directly indicative of the **volume of distribution (Vd)**. - Vd is a pharmacokinetic parameter that relates the total amount of drug in the body to the concentration of the drug in plasma, and it cannot be directly inferred from AUC values alone without additional information like dose and clearance. *Brand B has higher volume of distribution than brand A* - Similar to the previous option, AUC values alone are insufficient to determine the relative **volume of distribution** between the two brands. - Changes in Vd would affect the peak concentration (Cmax) and the elimination half-life, but a definitive conclusion requires more comprehensive pharmacokinetic analysis.

Question 366: The following plot of log dose of norepinephrine on X-axis and response in the form of increase in cardiac contractility on Y-axis represents?

A. Dose response curve
B. Quantal dose response curve
C. Graded dose response curve (Correct Answer)
D. Quantum dose response curve

Explanation: ***Graded dose response curve*** - This graph shows a **continuous increase in response** (cardiac contractility) as the **log dose of norepinephrine increases**, which is characteristic of a graded dose-response curve. - A graded dose-response curve represents the **magnitude of effect** observed from a single biological unit (e.g., cell, tissue, or individual) as a function of the drug dose. *Dose response curve* - This is a general term, but more specific labels like 'graded' or 'quantal' are used to distinguish the type of response measured. - It does not specify whether the response measured is continuous or all-or-none. *Quantal dose response curve* - A quantal dose-response curve describes the **percentage of a population** that exhibits a specific **all-or-none effect** at a given dose. - It would typically show the cumulative percentage of individuals responding as a function of dose, not a continuous response within a single unit. *Quantum dose response curve* - "Quantum dose response curve" is not a standard pharmacological term. - This term is likely a misspelling or incorrect interpretation of 'quantal dose response curve'.

Question 367: 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 368: What is the area under the curve between the earmarked points?

A. 68.2% (Correct Answer)
B. 95.4%
C. 99.7%
D. 50%

Explanation: ***68.2%*** - The image displays a **normal distribution curve**, with vertical lines likely representing standard deviations from the mean. - The "earmarked points" appear to be at **-1 standard deviation and +1 standard deviation** from the mean. The area between these points in a normal distribution is approximately **68.2%** (according to the empirical rule). - This represents the probability that a value falls within one standard deviation of the mean in a normal distribution. *95.4%* - This value represents the area between **-2 and +2 standard deviations** from the mean in a normal distribution. - The vertical lines in the image are closer to the **first standard deviation marks, not the second**. - This would be correct if the earmarked points were at ±2 standard deviations. *99.7%* - This value represents the area between **-3 and +3 standard deviations** from the mean in a normal distribution. - The vertical lines clearly **do not extend to three standard deviations** from the mean. - This represents nearly all values in a normal distribution. *50%* - This value would represent the area from the mean to one of the tails, or the area below or above the mean. - The **symmetrical placement of the two earmarked points** around the central peak (mean) indicates an area covering both sides, not just one half or a tail. - This does not represent the area between two symmetrical points around the mean.

Question 369: The following plot comparing pharmacokinetics of different ibuprofen brands is called:

A. Kaplan Meier plot
B. Spaghetti plot (Correct Answer)
C. Funnel plot
D. Forest plot

Explanation: ***Spaghetti plot*** - A **spaghetti plot** is characterized by multiple lines, each representing an individual's data across different time points or conditions, creating a visual resemblance to strands of spaghetti. This plot is ideal for visualizing **individual changes** and patterns in longitudinal data. - In pharmacokinetics, spaghetti plots are useful to compare the **drug concentration profiles** of different brands or formulations within individuals or across a group, showing individual variability. *Kaplan Meier plot* - A Kaplan-Meier plot (or survival curve) is used to estimate the **survival probability** over time for a group of individuals. - It displays a step-wise curve that decreases over time, representing the proportion of subjects **surviving** or remaining event-free, which is clearly not what is depicted in the image. *Funnel plot* - A **funnel plot** is a scatter plot used in meta-analyses to detect **publication bias** or small study effects. - It plots the study effect size against a measure of its precision (e.g., standard error), typically forming a triangular or funnel shape if no bias is present. *Forest plot* - A **forest plot** is a graphical display used in meta-analyses to illustrate the **results of individual studies** along with their pooled estimate. - Each study is represented by a square and a horizontal line indicating the effect size and its **confidence interval**, respectively.

Question 370: The maximum safe dose for Lignocaine (without adrenaline) as a local anaesthetic drug is :

A. 7 mg/kg
B. 5 mg/kg
C. 9 mg/kg
D. 3 mg/kg (Correct Answer)

Explanation: ***3 mg/kg*** - The maximum safe dose for **plain lignocaine** (without adrenaline) is **3 mg/kg**. - Exceeding this limit increases the risk of **systemic toxicity**, particularly central nervous system and cardiovascular effects. *7 mg/kg* - This dosage refers to the maximum safe dose of **lignocaine when combined with adrenaline**. - **Adrenaline causes vasoconstriction**, which delays systemic absorption of lignocaine, allowing for a higher total dose. *5 mg/kg* - This is also within the range of the maximum safe dose for **lignocaine with adrenaline**, though it is sometimes quoted as the upper limit for **plain lignocaine** by some references. - However, for plain lignocaine, **3 mg/kg is the more widely accepted and safer standard**. *9 mg/kg* - This dose is **significantly higher** than the recommended maximum for both plain and adrenaline-containing lignocaine. - Administering 9 mg/kg would carry a **very high risk of severe systemic toxicity**, including convulsions and cardiac arrest.

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