Pharmacokinetics and Pharmacodynamics — MCQs

Pharmacokinetics and Pharmacodynamics Indian Medical PG Practice Questions and MCQs

Question 371: Which of the following vaccines are given through the intramuscular route? 1. BCG vaccine 2. Hepatitis B vaccine 3. Pentavalent vaccine 4. Inactivated Polio vaccine

A. 1, 2 and 3
B. 2, 3 and 4 (Correct Answer)
C. 1, 3 and 4
D. 1, 2 and 4

Explanation: ***2, 3 and 4*** - The **Hepatitis B vaccine**, **Pentavalent vaccine** (DPT-Hib-HepB), and **Inactivated Polio Vaccine (IPV)** are all administered via the **intramuscular (IM)** route to ensure proper absorption and immune response. - Intramuscular injection is preferred for these vaccines to deliver antigens directly into muscle tissue, promoting effective antigen-presenting cell uptake. *1, 2 and 3* - This option incorrectly includes the **BCG vaccine**, which is administered intradermally, not intramuscularly. - The **BCG vaccine** creates a localized immune response in the skin, which is crucial for its protective mechanism against tuberculosis. *1, 3 and 4* - This combination is incorrect because it includes the **BCG vaccine**, which is given intradermally. - Administering **BCG intramuscularly** could lead to adverse reactions and reduce vaccine efficacy. *1, 2 and 4* - This option is incorrect as it again includes the **BCG vaccine**, which is administered **intradermally**. - Proper route of administration is critical for vaccine safety and effectiveness, and only **Hepatitis B, Pentavalent, and IPV** are given intramuscularly among the listed choices.

Question 372: Which one of the following statements regarding the composition of common crystalloid solutions is correct ?

A. Hartmann’s solution contains 111 meq/L of Na
B. Normal saline contains 130 meq/L of Cl
C. Normal saline contains 100 meq/L of Na
D. Hartmann’s solution contains 111 meq/L of Cl (Correct Answer)

Explanation: ***Hartmann’s solution contains 111 meq/L of Cl*** - **Hartmann's solution** (Lactated Ringer's) typically contains **111 mmol/L** (or meq/L) of chloride. - Its electrolyte composition aims to mimic plasma more closely than normal saline, with **lower chloride content** to reduce the risk of hyperchloremic acidosis. *Hartmann’s solution contains 111 meq/L of Na* - Hartmann's solution contains approximately **130 meq/L of Na**, not 111 meq/L. - The sodium concentration is higher than 111 meq/L to maintain **isotonicity** and match plasma osmolality. *Normal saline contains 130 meq/L of Cl* - **Normal saline (0.9% NaCl)** contains **154 meq/L of Cl**, which is significantly higher than 130 meq/L. - Its high chloride content can lead to **hyperchloremic metabolic acidosis** if administered in large volumes. *Normal saline contains 100 meq/L of Na* - **Normal saline (0.9% NaCl)** contains **154 meq/L of Na**, not 100 meq/L [1]. - This higher sodium concentration contributes to its **isotonicity** with plasma [1].

Question 373: 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 374: 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. A and D
B. A and C
C. A, C, D (Correct Answer)
D. A, B, D

Explanation: ***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.

Question 375: What would happen to the half-life and plasma concentration of a drug which follows first-order kinetics, if the dose is doubled?

A. Half - life and plasma concentration remains the same
B. Half - life doubles and plasma concentration remains the same
C. Half - life remains the same and plasma concentration doubles (Correct Answer)
D. Half - life and plasma concentration doubles

Explanation: ***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.

Question 376: Purpose of adding zinc to insulin in commercial preparations for treatment of diabetes mellitus is:-

A. To make it short acting
B. To make it fast acting
C. To make it long acting (Correct Answer)
D. Addition of zinc makes the insulin effective orally

Explanation: ***To make it long acting*** - **Zinc** is added to insulin formulations, particularly **neutral protamine Hagedorn (NPH) insulin**, to create larger crystal complexes [1]. - These larger complexes **slow down the absorption** of insulin from the subcutaneous injection site, thereby prolonging its duration of action [2]. *To make it short acting* - **Short-acting insulins** like regular insulin are not formulated with zinc, as their purpose is rapid onset and a shorter duration. - Adding zinc would counteract the desired rapid-acting pharmacokinetic profile. *To make it fast acting* - **Fast-acting insulins** (insulin analogs) have specific amino acid modifications that alter their self-association properties to ensure rapid absorption, not the addition of zinc [2]. - Zinc actually works against the goal of fast action by promoting aggregation. *Addition of zinc makes the insulin effective orally* - Insulin is a **peptide hormone** and is generally destroyed by digestive enzymes in the gastrointestinal tract, making oral administration ineffective regardless of zinc presence [3]. - Efforts to create oral insulin involve complex delivery systems, not simple zinc addition.

Question 377: True for lithium:

A. Can be given safely in renal dysfunction
B. Protein bound
C. Narrow therapeutic index (Correct Answer)
D. Delayed absorption

Explanation: ***Narrow therapeutic index*** - Lithium has a **narrow therapeutic index**, meaning the difference between its effective and toxic doses is small. - This necessitates **close monitoring of serum lithium levels** to ensure efficacy and prevent toxicity. *Can be given safely in renal dysfunction* - Lithium is **primarily excreted renally**, and its clearance is directly proportional to creatinine clearance. - Therefore, it **should be used with caution** (or avoided) in patients with renal dysfunction due to increased risk of toxicity. *Protein bound* - Lithium is **not protein-bound**; it exists as a free ion in the blood. - This characteristic contributes to its rapid distribution and excretion. *Delayed absorption* - Lithium is **rapidly and almost completely absorbed** from the gastrointestinal tract. - Peak plasma concentrations are usually reached within 1-2 hours for immediate-release preparations.

Question 378: The shortest acting opioid is:-

A. Remifentanil (Correct Answer)
B. Fentanyl
C. Alfentanil
D. Sufentanil

Explanation: ***Remifentanil*** - **Remifentanil** is an **ultra-short-acting opioid** due to its unique metabolism by **non-specific plasma and tissue esterases**. - Its rapid metabolism results in a very short context-sensitive half-time, meaning its effects **terminate quickly** regardless of infusion duration. *Alfentanil* - **Alfentanil** is a **short-acting opioid** but its duration of action is longer than remifentanil. - It is eliminated primarily by **hepatic metabolism**, which is slower than esterase-based metabolism. *Fentanyl* - **Fentanyl** is a **potent synthetic opioid** with an intermediate duration of action. - Its elimination is dependent on **hepatic metabolism**, and it has a longer context-sensitive half-time compared to remifentanil. *Sufentanil* - **Sufentanil** is a **very potent opioid** with a longer duration of action than fentanyl and alfentanil. - Its metabolism is hepatic, leading to a **longer elimination half-life** and thus a more prolonged effect.

Question 379: Atorvastatin is used as an anti-dyslipidemic drug. These drugs inhibit their target enzyme by:-

A. Noncompetitive inhibition
B. Competitive inhibition (Correct Answer)
C. Irreversible inhibition
D. Uncompetitive inhibition

Explanation: ***Competitive inhibition*** - Atorvastatin is a **statin**, which acts as a **competitive inhibitor** of **HMG-CoA reductase**, the rate-limiting enzyme in cholesterol synthesis. - It competes with the natural substrate, HMG-CoA, for binding to the **active site of the enzyme**, thereby reducing cholesterol production. *Uncompetitive* - **Uncompetitive inhibitors** bind only to the **enzyme-substrate complex**, not to the free enzyme. - This type of inhibition is characterized by a decrease in both **apparent Vmax** and **apparent Km**. *Noncompetitive inhibition* - **Noncompetitive inhibitors** bind to an allosteric site on the enzyme, distinct from the active site, and can bind to either the **free enzyme or the enzyme-substrate complex**. - This leads to a decrease in the **apparent Vmax** but does not affect Km. *Irreversible inhibition* - **Irreversible inhibitors** form a **strong covalent bond** with the enzyme, permanently inactivating it. - Statins do not form covalent bonds with HMG-CoA reductase; their inhibition is **reversible** upon drug discontinuation.

Question 380: 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.

Practice by Chapter

Absorption and Bioavailability

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Drug Distribution and Protein Binding

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Biotransformation and Metabolism Pathways

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Renal and Non-renal Excretion

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Compartment Models

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Dose-Response Relationships

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Drug Efficacy and Potency

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Drug Tolerance and Tachyphylaxis

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Population Pharmacokinetics

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Pharmacokinetic Variability

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