Pharmacokinetics and Pharmacodynamics Practice Questions

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.

Q: Which of the following is a G protein coupled receptor?

M2 muscarinic receptor. ***M2 muscarinic receptor***- The **M2 muscarinic receptor** is a classic example of a **G protein-coupled receptor (GPCR)** [1]. When a ligand binds to a G-protein-coupled receptor, it triggers a mechanism where GDP is exchanged for GTP, causing the G-protein's alpha subunit to separate and initiate signaling pathways [1]. These heterotrimeric G-proteins couple cell surface receptors to catalytic units that form second messengers or directly to ion channels [1]. GPCRs are important regulators of nerve activity in the CNS and are receptors for neurotransmitters of the peripheral autonomic nervous system, with acetylcholine (ACh) being a ligand that regulates functions of glands and smooth muscle [2]. The **M2 muscarinic receptor** specifically activates an **inhibitory G protein (G_i)**, leading to a decrease in **cAMP** and opening of **potassium channels**. The effects of metabotropic receptors, like GPCRs, can last tens of seconds to minutes, contrasting with the brief effects of ionotropic receptors [4].*NMDA receptor*- The **NMDA receptor** is a **ligand-gated ion channel** that allows the influx of calcium and sodium ions [3]. It does not couple to G proteins, but directly mediates ion flow upon activation by **glutamate** and **glycine**. Ligand-gated ion channels open a central transmembrane ion channel when a neurotransmitter binds to sites on its extracellular domain [3].*Steroid*- **Steroid hormones** primarily act on **intracellular receptors** that, once activated, translocate to the nucleus to regulate gene expression. They are not cell surface receptors and do not utilize G protein signaling.*Insulin receptors*- **Insulin receptors** are **receptor tyrosine kinases** that, upon binding insulin, undergo autophosphorylation and activate intracellular signaling pathways. They signal through a cascade of protein phosphorylations, not through G proteins.

Q: Which is true for glucuronidation:

Phase II reaction. ***Phase II reaction***- **Glucuronidation** is a major **Phase II** metabolic pathway that conjugates a glucuronic acid molecule to a **lipophilic substance** [1]- This process significantly increases the **water solubility** of the substance, facilitating its excretion from the body [1, 2]- Catalyzed by **UDP-glucuronosyltransferases (UGTs)**, a family of conjugation enzymes [1]*Done by CYP enzyme*- **CYP (cytochrome P450)** enzymes are primarily involved in **Phase I** metabolic reactions, which typically functionalize compounds through oxidation, reduction, or hydrolysis [1]- Glucuronidation is catalyzed by **UDP-glucuronosyltransferases (UGTs)**, not CYP enzymes [1]*Phase I reaction*- **Phase I reactions** (e.g., oxidation, reduction, hydrolysis) introduce or expose polar functional groups on xenobiotics [1]- Glucuronidation is a **conjugation reaction**, characteristic of **Phase II metabolism**, not Phase I [1]*Water solubility is decreased*- Glucuronidation involves the attachment of a **hydrophilic glucuronic acid** molecule to the substrate [1]- This conjugation significantly **increases the water solubility** of the metabolite, which is essential for its efficient urinary or biliary excretion [1, 2]- The addition of the polar glucuronic acid group makes lipophilic compounds more water-soluble [1]

Q: After IV drug administration, elimination of a drug depends on:

Clearance. ***Clearance*** - **Clearance (CL)** is the primary and direct determinant of drug elimination after IV administration. - It represents the **volume of plasma cleared of drug per unit time** (e.g., mL/min or L/hr). - The **rate of elimination** is directly calculated as: Rate = CL × Plasma concentration - Clearance integrates the efficiency of all eliminating organs (liver, kidneys) and is the key parameter determining how fast a drug is removed from the body. - Formula: **CL = Rate of elimination / Plasma concentration** *Lipid solubility* - Lipid solubility affects drug **distribution** and **renal reabsorption** but does not directly determine the rate of elimination. - Highly lipid-soluble drugs may be reabsorbed in renal tubules, but the elimination rate is still governed by clearance. - Lipid solubility is more relevant to drug distribution and metabolism pathways than to the rate of elimination itself. *Volume of distribution* - Volume of distribution (Vd) describes how extensively a drug distributes into tissues versus plasma. - While Vd affects the **half-life** (t½ = 0.693 × Vd/CL), it does NOT directly determine the elimination rate. - A large Vd means more drug in tissues, which affects how long elimination takes, but the actual rate of elimination is still determined by clearance. - Vd is a distribution parameter, not an elimination parameter. *All of the options* - This is incorrect because only **clearance** directly determines the rate of drug elimination. - While lipid solubility and volume of distribution can indirectly influence how long a drug remains in the body, they do not determine the elimination rate itself—clearance does.

Q: All of the following are advantages of transdermal drug delivery systems except

They produce high peak plasma concentration of the drug. ***They produce high peak plasma concentration of the drug*** - Transdermal drug delivery generally aims to provide **sustained**, **controlled drug release** over an extended period, leading to relatively **flat plasma concentration profiles**, not high peaks [1]. - High peak concentrations are more characteristic of bolus intravenous injections or immediate-release oral formulations, which can lead to rapid onset but also potentially higher **adverse effects** [1]. *They minimize interindividual variation in the achieved plasma drug concentration* - Transdermal systems often contribute to **consistent drug absorption**, bypassing factors like gastric emptying time, gut motility, and food interactions, which can vary significantly between individuals. - This consistency helps in achieving more **predictable plasma drug levels** compared to oral routes, reducing variability [4]. *They avoid hepatic first pass metabolism of the drug* - Drugs administered transdermally are absorbed directly into the **systemic circulation**, bypassing the **portal venous system** and liver entirely [4]. - This means the drug avoids being metabolized by **hepatic enzymes** before reaching its site of action, increasing its **bioavailability** [4]. *They produce smooth and nonfluctuating plasma concentration of the drug* - Transdermal patches are designed for **continuous drug release** at a controlled rate, maintaining therapeutic levels of the drug in the blood [2], [3]. - This **steady-state drug delivery** helps avoid the "peaks and troughs" seen with intermittent dosing, which can be associated with side effects or suboptimal efficacy [3].

Q: All of these fluids are isotonic except

3% Normal saline. ***3% Normal saline*** - This fluid is **hypertonic**, meaning it has a higher solute concentration (osmolality ~1025 mOsm/L) than normal body fluids (~280-295 mOsm/L). - It is definitively **not isotonic** [1] and is used to correct severe hyponatremia by drawing water from the intracellular to the extracellular space. - This is the **clearest answer** as it is unambiguously non-isotonic. *5% dextrose* - This solution is **isotonic when infused** (~252 mOsm/L, close to plasma osmolality) but becomes **hypotonic physiologically** as the dextrose is rapidly metabolized, leaving free water [1]. - While technically isotonic at administration, it behaves as a hypotonic solution in the body. - Commonly used for dehydration and as a vehicle for medications. *0.9% Normal saline* - Often called **normal saline**, this is an **isotonic** crystalloid solution (~308 mOsm/L), with osmolality similar to blood plasma [1]. - Widely used for volume expansion, rehydration, and as a maintenance fluid in various clinical settings. *Ringer lactate* - This is an **isotonic** crystalloid solution (~273 mOsm/L) containing sodium, chloride, potassium, calcium, and lactate. - It closely mimics the electrolyte composition of plasma and is preferred for fluid resuscitation and in surgical settings due to its balanced composition.

Question 1

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 2

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

Accepted Answer

16

Answer

8

Answer

1024

Answer

128

Question 3

Therapeutic index of a drug is an indicator of:-

Accepted Answer

Safety

Answer

All of these

Answer

Potency

Answer

Efficacy

Question 4

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

Question 5

Which of the following is a G protein coupled receptor?

Accepted Answer

M2 muscarinic receptor

Answer

NMDA receptor

Answer

Insulin receptors

Answer

Steroid receptors

Question 6

Which is true for glucuronidation:

Accepted Answer

Phase II reaction

Answer

Done by CYP enzyme

Answer

Phase I reaction

Answer

Water solubility is decreased

Question 7

After IV drug administration, elimination of a drug depends on:

Accepted Answer

Clearance

Answer

Lipid solubility

Answer

Volume of distribution

Answer

All of the options

Question 8

Which one of the following is true for competitive antagonism?

Accepted Answer

Agonist and competitive antagonist bind to the same receptor

Answer

Agonist cannot displace an antagonist from the receptor

Answer

Antagonism cannot be completely reversed by an increased dose of an agonist

Answer

Maximum response (Emax) is reduced in the presence of a competitive antagonist

Question 9

All of the following are advantages of transdermal drug delivery systems except

Accepted Answer

They produce high peak plasma concentration of the drug

Answer

They minimize interindividual variation in the achieved plasma drug concentration

Answer

They avoid hepatic first pass metabolism of the drug

Answer

They produce smooth and nonfluctuating plasma concentration of the drug

Question 10

All of these fluids are isotonic except

Accepted Answer

3% Normal saline

Answer

5% dextrose

Answer

0.9% Normal saline

Answer

Ringer lactate

Pharmacokinetics and Pharmacodynamics — MCQs

Pharmacokinetics and Pharmacodynamics — MCQs

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