Pharmacokinetics and Pharmacodynamics Practice Questions

Q: Zero order kinetics means:

A constant amount of drug is eliminated per unit time. **Explanation:** **Zero-order kinetics** occurs when the rate of drug elimination is independent of the plasma concentration. This typically happens when the metabolic enzymes or transport systems responsible for elimination become **saturated** [1]. Therefore, a **constant amount** (e.g., 10 mg/hour) of the drug is eliminated per unit time, regardless of how much drug is in the body [2]. **Analysis of Options:** * **Option A (Correct):** This is the definition of zero-order kinetics. The elimination rate is constant (Rate = k). * **Option B (Incorrect):** This describes **First-order kinetics**, where a constant *fraction* or percentage (e.g., 10% per hour) is eliminated [2]. Most drugs follow first-order kinetics at therapeutic doses [1]. * **Option C (Incorrect):** This is the definition of **Bioavailability (F)**. * **Option D (Incorrect):** This refers to **Enzyme Induction**, which increases the rate of metabolism but does not define the order of kinetics. **High-Yield Clinical Pearls for NEET-PG:** 1. **Mnemonic for Zero-Order Drugs:** **"WATT"** or **"Zero WATTS"** * **W**arfarin (at high doses) * **A**lcohol (Ethanol) - *Most common example* [1] * **T**heophylline * **T**olbutamide * **S**alicylates (Aspirin) and **P**henytoin (at high doses) [1] 2. **Key Differences:** * **First-order:** Half-life ($t_{1/2}$) is constant. * **Zero-order:** Half-life ($t_{1/2}$) is not constant; it decreases as the concentration decreases. 3. **Capacity-limited elimination:** Zero-order kinetics is also known as "saturation" or "Michaelis-Menten" kinetics [2]. When a drug shifts from first-order to zero-order (like Phenytoin), it can lead to a sudden, toxic rise in plasma levels with small dose increases [1].

Q: Which of the following factors has the maximum effect on the filtration of a drug by the glomerulus?

Plasma protein binding. **Explanation:** **Glomerular filtration** is a passive process where drugs are filtered through the capillary pores of the glomerulus [1]. The primary determinant of this process is the **molecular size** and the **free (unbound) fraction** of the drug [2]. 1. **Why Plasma Protein Binding is Correct:** Drugs in the plasma exist in two forms: bound to proteins (like albumin) and free. The glomerular filtration barrier acts as a sieve that prevents large molecules like plasma proteins from passing through [3]. Consequently, any drug molecule bound to a protein becomes too large to be filtered. Therefore, the **rate of filtration is directly proportional to the free fraction** of the drug [2]. High protein binding significantly limits glomerular filtration. 2. **Why Other Options are Incorrect:** * **Lipid Solubility & Degree of Ionization:** Unlike tubular reabsorption (which is highly dependent on lipid solubility and pH-dependent ionization), glomerular filtration is a bulk flow process through large pores [1]. It does not require the drug to cross lipid membranes; thus, lipid solubility and ionization have **no significant effect** on filtration. * **Rate of Tubular Secretion:** This is a separate process occurring in the renal tubules via active transporters (e.g., OAT, OCT). While it contributes to the total renal clearance, it does not influence the filtration occurring at the glomerulus [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Glomerular Filtration Rate (GFR):** Only the **unbound** drug is filtered [2]. * **Tubular Secretion:** Can clear both **bound and unbound** drugs (e.g., Penicillin is highly protein-bound but rapidly cleared via secretion) [2]. * **Tubular Reabsorption:** Highly dependent on **Lipid solubility** and **pH** (Ion trapping). * **Formula:** Renal Clearance = (Filtration + Secretion) – Reabsorption.

Q: Which of the following drugs is metabolized through glycin(e) conjugation?

Nicotinic acid. **Explanation:** **Correct Option: D (Nicotinic acid)** Metabolism occurs via two main phases: Phase I (Functionalization) and Phase II (Conjugation). **Glycine conjugation** is a specific Phase II pathway used for compounds containing a carboxylic acid group. **Nicotinic acid (Niacin)** and **Salicylates** (Aspirin) are the classic examples of drugs metabolized through this pathway. In this process, the drug is activated to a Coenzyme A thioester, which then reacts with glycine to form a water-soluble conjugate (e.g., nicotinuric acid) for renal excretion. **Analysis of Incorrect Options:** * **A. Benzodiazepines:** These drugs primarily undergo Phase I oxidation (via CYP3A4/2C19) followed by **Glucuronidation** (Phase II). Note: "LOT" drugs (Lorazepam, Oxazepam, Temazepam) undergo direct glucuronidation, bypassing Phase I. * **B. Atazanavir:** This protease inhibitor is extensively metabolized in the liver primarily by the **CYP3A4** isoenzyme (Phase I). * **C. Ifosfamide:** This alkylating agent is a prodrug that requires activation by **CYP3A4 and CYP2B6** (Phase I) to form its active metabolite, ifosfamide mustard. **High-Yield Clinical Pearls for NEET-PG:** * **Phase II Conjugation Mnemonic:** Remember **"S-G-A-G"** (Sulfation, Glucuronidation, Acetylation, Glycine conjugation). * **Glucuronidation** is the most common Phase II reaction. * **Acetylation** shows genetic polymorphism (Fast vs. Slow acetylators); drugs involved include **S**ulfonamides, **H**ydralazine, **I**soniazid, and **P**rocainamide (**SHIP**). * **Gray Baby Syndrome** occurs in neonates due to a deficiency of **UDP-glucuronyltransferase**, preventing the conjugation of Chloramphenicol.

Q: Which of the following terms best describes a drug that blocks the action of adrenaline at its receptors by occupying those receptors without activating them?

Pharmacologic antagonist. ### Explanation **1. Why Option A is Correct:** A **pharmacologic antagonist** is a drug that binds to the same receptor as an agonist (in this case, adrenaline) but does not activate it. By occupying the receptor site, it prevents the agonist from binding and exerting its effect. This is the classic definition of receptor-level blockade. Since it competes for the same binding site, it is also often referred to as a competitive antagonist. **2. Why the Other Options are Incorrect:** * **B. Non-competitive antagonist:** These drugs do not simply "occupy" the receptor site to block the agonist; they either bind irreversibly to the active site or bind to an **allosteric site**, changing the receptor's shape so the agonist cannot trigger a response. Unlike pharmacologic antagonists, their effect cannot be overcome by increasing agonist concentration. * **C. Physiologic antagonist:** This refers to two drugs acting on **different receptors** to produce opposite effects in the same system. *Example:* Histamine (bronchoconstriction via H1) vs. Adrenaline (bronchodilation via β2). * **D. Chemical antagonist:** This involves a direct chemical reaction between two substances in solution, neutralizing the drug before it reaches a receptor. *Example:* Protamine sulfate neutralizing Heparin. **3. NEET-PG High-Yield Pearls:** * **Competitive Antagonism:** Shifts the Dose-Response Curve (DRC) to the **right** (increases $EC_{50}$), but the **maximal efficacy ($E_{max}$) remains unchanged**. * **Non-competitive Antagonism:** Flattens the DRC, **decreasing the $E_{max}$**, while the $EC_{50}$ usually remains the same. * **Inverse Agonist:** Binds to the same receptor as an agonist but produces an effect **opposite** to that of the agonist (e.g., Beta-carbolines at GABA receptors).

Q: Which of the following terms best describes the antagonism of the bronchoconstrictor effect of leukotrienes (mediated at leukotriene receptors) by terbutaline (acting at adrenoceptors) in a patient with asthma?

Physiologic antagonist. **Explanation:** The correct answer is **Physiologic antagonist (Option C)**. **1. Why it is correct:** Physiologic (or functional) antagonism occurs when two drugs act on **different receptors** to produce **opposing physiological effects** on the same biological system [1]. In this scenario: * **Leukotrienes** act on leukotriene receptors to cause bronchoconstriction [4]. * **Terbutaline** acts on $\beta_2$-adrenoceptors to cause bronchodilation [1], [3]. Because they achieve opposite results (constriction vs. dilation) through independent pathways, they are physiologic antagonists. **2. Why the other options are wrong:** * **Pharmacologic antagonist (A):** This involves a drug binding to the **same receptor** as the agonist to block its action (e.g., Montelukast blocking leukotriene receptors). * **Partial agonist (B):** This is a drug that binds to the same receptor as a full agonist but produces a sub-maximal response (e.g., Pindolol at $\beta$-receptors) [2]. * **Chemical antagonist (D):** This occurs when two substances react **chemically** with each other in solution, neutralizing the drug before it reaches a receptor (e.g., Protamine neutralizing Heparin or Chelating agents). **Clinical Pearls for NEET-PG:** * **Classic Example:** Histamine (H1 receptors) vs. Adrenaline ($\beta_2$ receptors) in anaphylaxis is the most frequently tested example of physiologic antagonism. * **Glucagon vs. Insulin:** These are physiologic antagonists regarding blood glucose levels. * **Key Distinction:** Unlike competitive antagonism, physiologic antagonism cannot be fully overcome by simply increasing the dose of the agonist, as the mechanisms are independent.

Question 1

A bolus of drug K is given intravenously. The drug is noted to follow first-order kinetics. Which of the following describes the elimination of drug K?

Accepted Answer

The rate of elimination of drug K is proportional to its concentration in the patient's plasma.

Answer

The rate of elimination of drug K is dependent on a nonlinear relationship to the plasma protein concentration.

Answer

The rate of elimination of drug K is constant.

Answer

The rate of elimination of drug K is proportional to the patient's renal function.

Question 2

Which of the following statements about drug absorption is false?

Accepted Answer

Acidic drugs are absorbed when pH < Pka.

Answer

Glucose absorption through SGLT-1 is active.

Answer

Most drugs are absorbed by passive diffusion.

Answer

Basic drugs are absorbed when pH > Pka.

Question 3

Zero order kinetics means:

Accepted Answer

A constant amount of drug is eliminated per unit time

Answer

A constant fraction of the drug in the body is eliminated per unit time

Answer

The fraction of the administered dose that reaches the systemic circulation.

Answer

The effect that can be increased by giving a second agent that boosts the effect of the liver's enzyme system

Question 4

Side effects of a drug arise due to interactions of the drug with molecules other than its target. These effects can be minimized by the drug's high:

Accepted Answer

Specificity

Answer

Solubility

Answer

Affinity

Answer

Hydrophobicity

Question 5

Which is the most appropriate definition of spare receptors?

Accepted Answer

Receptors that remain unoccupied even after a drug produces its maximal response.

Answer

Receptors involved in the binding of inverse agonists.

Answer

Receptors that are responsible for producing adverse drug effects.

Answer

Receptors that are unable to produce a maximum response.

Question 6

Which of the following is NOT a characteristic of active drug transport?

Accepted Answer

Carrier transport is nonsaturable

Answer

Energy dependent

Answer

Makes use of specific transporter proteins

Answer

Carries the drug against the concentration gradient

Question 7

Which of the following factors has the maximum effect on the filtration of a drug by the glomerulus?

Accepted Answer

Plasma protein binding

Answer

Lipid solubility

Answer

Degree of ionization

Answer

Rate of tubular secretion

Question 8

Which of the following drugs is metabolized through glycin(e) conjugation?

Accepted Answer

Nicotinic acid

Answer

Benzodiazepines

Answer

Atzanavir

Answer

Ifosfamide

Question 9

Which of the following terms best describes a drug that blocks the action of adrenaline at its receptors by occupying those receptors without activating them?

Accepted Answer

Pharmacologic antagonist

Answer

Non-competitive antagonist

Answer

Physiologic antagonist

Answer

Chemical antagonist

Question 10

Which of the following terms best describes the antagonism of the bronchoconstrictor effect of leukotrienes (mediated at leukotriene receptors) by terbutaline (acting at adrenoceptors) in a patient with asthma?

Accepted Answer

Physiologic antagonist

Answer

Pharmacologic antagonist

Answer

Partial agonist

Answer

Chemical antagonist

Pharmacokinetics and Pharmacodynamics — MCQs

Pharmacokinetics and Pharmacodynamics — MCQs

On this page

Practice by Chapter

Want unlimited practice?