Pharmacokinetics and Pharmacodynamics Practice Questions

Q: 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?

Graded dose response curve. ***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'.

Q: Which of the following statement is correct regarding the given DRC? (AllMS Nov 2016)

A and B are full agonists. ***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.

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

3 mg/kg. ***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.

Q: Choose the correct options regarding the route of administration and bioavailability. A- Intravenous =1 B- 0.75< Oral <1 C-0.75 <IM ≤ 1 D- 0.75<SC ≤ 1 IM - Intramuscular SC- Subcutaneous

A, C, D. ***A, C, D*** - Intravenous (IV) administration has **100% bioavailability** because the drug enters the systemic circulation directly, bypassing any absorption barriers. - Intramuscular (IM) and subcutaneous (SC) routes generally have **high bioavailability**, often between 75% and 100%, as drugs are absorbed directly into the bloodstream without first-pass metabolism. *A and D* - While options A and D are correct, this choice is incomplete as option C is also a correct statement regarding bioavailability. - IM administration typically results in high systemic bioavailability, similar to SC, making its exclusion here incorrect. *A and C* - While options A and C are correct, this choice is incomplete as option D is also a correct statement regarding bioavailability. - Subcutaneous administration also generally results in high bioavailability, as absorption tends to be complete. *A, B, D* - While options A and D are correct, option B is typically incorrect for oral bioavailability. - Oral bioavailability of many drugs is often less than 0.75 (75%) due to factors like **first-pass metabolism** and incomplete absorption in the gastrointestinal tract.

Q: What would happen to the half-life and plasma concentration of a drug which follows first-order kinetics, if the dose is doubled?

Half - life remains the same and plasma concentration doubles. ***Half - life remains the same and plasma concentration doubles*** - In **first-order kinetics**, drug elimination is proportional to the **plasma concentration**, meaning a constant *fraction* of the drug is eliminated per unit of time. - Doubling the dose will **double the initial plasma concentration**, but the **half-life** (time taken for plasma concentration to halve) remains constant because the *rate of elimination proportionally increases* with concentration. *Half - life and plasma concentration remains the same* - This would only be true if the dose was not changed, or if the drug followed **zero-order kinetics** and the elimination system was already saturated, which is not the case here. - If the plasma concentration remained the same after doubling the dose, it would imply either no absorption or extremely rapid elimination, contradicting typical first-order drug behavior. *Half - life doubles and plasma concentration remains the same* - For **half-life to double**, there would need to be a **decrease in drug clearance** or an *increase in volume of distribution*, not simply a dose increase. - If plasma concentration remained the same despite a doubled dose, it would suggest a **major increase in clearance** or volume of distribution, which is not stated. *Half life and plasma concentration doubles* - While plasma concentration doubles with a doubled dose in **first-order kinetics**, the **half-life remains constant**. - Half-life is an **intrinsic pharmacokinetic parameter** determined by clearance and volume of distribution, not by the administered dose in first-order kinetics.

Q: Find therapeutic index of drug from the information given below in the graph

16. ***16*** - The **therapeutic index (TI)** is calculated as **TD50/ED50**, which is the ratio of the **toxic dose in 50% of the population (TD50)** to the **effective dose in 50% of the population (ED50)**. - From the graph, the **ED50** (response curve) is **8 units**, and the **TD50** (toxicity curve) is **128 units**. Therefore, TI = 128 / 8 = **16**. *8* - This value represents the **effective dose in 50% of the population (ED50)**, not the therapeutic index. - **ED50** is the dose at which 50% of individuals exhibit the desired therapeutic effect. *1024* - This value is obtained by squaring 32 or cubing 8, which is not the correct way to calculate the **therapeutic index**. - There is no direct pharmacological calculation that would yield this number from the given ED50 and TD50 values. *128* - This value represents the **toxic dose in 50% of the population (TD50)**, not the therapeutic index. - **TD50** is the dose at which 50% of individuals experience a specified toxic effect.

Q: Therapeutic index of a drug is an indicator of:-

Safety. ***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.

Q: Pharmacodynamics deals with:-

Mechanism of action of a drug. Detailed study of the **Mechanism of action of a drug** [1][2] - **Pharmacodynamics** describes what the **drug does to the body**, including its **molecular targets** and biochemical effects [3]. - This involves the study of the drug's mechanisms to produce its therapeutic or toxic effects [2]. *Latency of onset* - **Latency of onset** refers to the time it takes for a drug to start producing its effects, which is a pharmacokinetic rather than a pharmacodynamic parameter. - It deals with the drug's absorption and distribution rather than its interaction with the body once it reaches its site of action. *Transport of drug across the biological membranes* - The **transport of drugs across biological membranes** is a key aspect of **pharmacokinetics**, specifically absorption and distribution [1]. - This process determines how much drug reaches its target site, not how it interacts with the target. *Mode of excretion of a drug* - The **mode of excretion** of a drug (e.g., renal, hepatic) falls under **pharmacokinetics**, addressing how the body gets rid of the drug. - This process influences the drug's duration of action and elimination half-life, not its mechanism of action.

Question 1

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?

Accepted Answer

Graded dose response curve

Answer

Dose response curve

Answer

Quantal dose response curve

Answer

Quantum dose response curve

Question 2

Which of the following statement is correct regarding the given DRC? (AllMS Nov 2016)

Accepted Answer

A and B are full agonists

Answer

C is non-competitive antagonist

Answer

B is more potent than A

Answer

A is more efficacious than B

Question 3

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

Accepted Answer

3 mg/kg

Answer

7 mg/kg

Answer

5 mg/kg

Answer

9 mg/kg

Question 4

Which of the following statements is correct regarding the given graph?

Accepted Answer

Drug 1 represents agonist and drug 4 represents inverse agonist

Answer

Drug 1 represents agonist and drug 2 represents inverse agonist

Answer

Drug 3 represents agonist and drug 4 represents inverse agonist

Answer

Drug 2 represents partial agonist and drug 3 represents inverse agonist

Question 5

Which of the following is true about clinical therapeutic index?

Accepted Answer

Dose in which efficacy and toxicity can be balanced in an individual

Answer

Therapeutic index is LD50/ED50

Answer

It is only used for a specific individual

Answer

It measures therapeutic index in populations rather than individuals

Question 6

Choose the correct options regarding the route of administration and bioavailability.
A- Intravenous =1
B- 0.75< Oral <1
C-0.75 <IM ≤ 1
D- 0.75<SC ≤ 1
IM - Intramuscular
SC- Subcutaneous

Accepted Answer

A, C, D

Answer

A and D

Answer

A and C

Answer

A, B, D

Question 7

What would happen to the half-life and plasma concentration of a drug which follows first-order kinetics, if the dose is doubled?

Accepted Answer

Half - life remains the same and plasma concentration doubles

Answer

Half - life and plasma concentration remains the same

Answer

Half - life doubles and plasma concentration remains the same

Answer

Half - life and plasma concentration doubles

Question 8

Find therapeutic index of drug from the information given below in the graph

Accepted Answer

16

Answer

8

Answer

1024

Answer

128

Question 9

Therapeutic index of a drug is an indicator of:-

Accepted Answer

Safety

Answer

All of these

Answer

Potency

Answer

Efficacy

Question 10

Pharmacodynamics deals with:-

Accepted Answer

Mechanism of action of a drug

Answer

Latency of onset

Answer

Transport of drug across the biological membranes

Answer

Mode of excretion of a drug

Pharmacokinetics and Pharmacodynamics — MCQs

Pharmacokinetics and Pharmacodynamics — MCQs

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