Pharmacokinetics and Pharmacodynamics — MCQs
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In the context of pharmacology, which plasma protein do acidic drugs primarily bind to?
Which of the following factors influences the duration of action of a drug?
Which drug is commonly administered via subdermal implant?
What is the effect of adding epinephrine to lignocaine (a local anesthetic)?
Which anaesthetic agent is neither metabolised by liver nor by kidney?
Which of the following statements about the biodisposition of penicillins and cephalosporins is NOT accurate?
Which of the following is not a phase I reaction?
Neuromuscular blocker of choice in renal failure is:
Which of the following best demonstrates the variability in drug responsiveness among individuals?
Which muscle relaxant is primarily excreted by the kidneys?
Pharmacokinetics and Pharmacodynamics Indian Medical PG Practice Questions and MCQs
Question 481: In the context of pharmacology, which plasma protein do acidic drugs primarily bind to?
- A. Globulin
- B. Albumin (Correct Answer)
- C. α1-acid glycoprotein
- D. None of the options
Explanation: ***Albumin*** - **Albumin** is the most abundant plasma protein and has multiple binding sites for a wide range of drugs, particularly **acidic drugs**. - Its high concentration and diverse binding capabilities make it the primary transporter for many **lipophilic** and **anionic drugs**. *Globulin* - **Globulins** are a diverse group of proteins, some of which bind to drugs, but they primarily transport **hormones**, **metals**, and **vitamins**, not acidic drugs. - They are less significant for binding acidic drugs compared to albumin. *α1-acid glycoprotein* - **α1-acid glycoprotein** primarily binds to **basic drugs** due to its numerous acidic residues. - While it plays a crucial role in binding basic compounds, it has limited affinity for acidic drugs. *None of the options* - This option is incorrect because **albumin** is a well-established and significant plasma protein for binding acidic drugs. - Specific plasma proteins are known to bind different types of drugs, and for acidic drugs, albumin is the primary binder.
Question 482: Which of the following factors influences the duration of action of a drug?
- A. Bioavailability
- B. Clearance
- C. Rate of elimination
- D. All of the options (Correct Answer)
Explanation: ***All of the options*** - **Clearance** and **rate of elimination** are the primary determinants of how long a drug stays in the body at therapeutic levels, thus directly influencing its duration of action. - **Bioavailability** affects the intensity and onset but can influence the perceived duration if subtherapeutic concentrations are achieved. - The interplay of these pharmacokinetic parameters ultimately determines the drug's therapeutic window and frequency of dosing. *Clearance* - **Clearance** is the rate at which the active drug is removed from the body, primarily by the kidneys and liver. - A higher clearance generally leads to a shorter elimination half-life and a **shorter duration of action**, as the drug is removed more quickly from the systemic circulation. *Rate of elimination* - The **rate of elimination** directly dictates how quickly the concentration of a drug in the body decreases over time. - A faster elimination rate (shorter half-life) means the drug's effects will wear off sooner, resulting in a **shorter duration of action**. - This is quantified by the elimination rate constant (Kel) and half-life (t½). *Bioavailability* - **Bioavailability** refers to the fraction of an administered dose of unchanged drug that reaches the systemic circulation. - While bioavailability primarily affects the **peak concentration (Cmax)** and **intensity** of drug effect, it can indirectly influence duration. - If bioavailability is very low, therapeutic concentrations may not be sustained long enough, effectively shortening the **clinically relevant duration of action**. - However, two drugs with identical elimination rates but different bioavailabilities will have the same elimination half-life and similar duration at therapeutic doses.
Question 483: Which drug is commonly administered via subdermal implant?
- A. Nicotine
- B. Fentanyl
- C. GTN
- D. Progestin (Correct Answer)
Explanation: ***Progestin*** - **Progestins** (synthetic progestogens like **etonogestrel**) are commonly administered via subdermal implant (e.g., **Nexplanon**, Implanon) for **long-acting reversible contraception (LARC)**. - This method provides a continuous, low dose of hormone, offering effective birth control for **3 years**. - The implant is a small, flexible rod inserted subdermally in the upper arm. *Nicotine* - **Nicotine** is typically administered via **transdermal patches**, gum, inhalers, or nasal sprays for **smoking cessation**, not subdermal implants. - While it's delivered transdermally, the mechanism is through a patch placed on the skin surface, not an implant beneath it. *Fentanyl* - **Fentanyl** is a potent opioid primarily delivered via **transdermal patches** for chronic pain management, or intravenously for acute pain. - It is not administered via a subdermal implant; patches provide continuous release through skin absorption. *GTN* - **Glyceryl trinitrate (GTN)**, or nitroglycerin, is commonly administered as **sublingual tablets** or **transdermal patches** for angina. - It has a very short half-life and is not suitable for a slow-release subdermal implant due to its rapid vasodilatory effects.
Question 484: What is the effect of adding epinephrine to lignocaine (a local anesthetic)?
- A. Increases distribution of local anesthetic
- B. Decreases absorption of local anesthetic (Correct Answer)
- C. Decreases duration of local anesthetic
- D. Increases metabolism of local anesthetic
Explanation: ***Decreases absorption of local anesthetic*** - Epinephrine causes **vasoconstriction** at the site of injection, which reduces the rate at which the local anesthetic is absorbed into the systemic circulation. - This slower absorption leads to a **higher concentration of the anesthetic** at the nerve fibers, prolonging its effect and reducing systemic toxicity. - This is the primary mechanism by which epinephrine enhances local anesthetic efficacy. *Increases distribution of local anesthetic* - The primary effect of epinephrine is to **localize the anesthetic** by reducing its systemic distribution. - This localization is achieved through **vasoconstriction**, which keeps the drug at the desired site rather than allowing it to distribute widely. *Decreases duration of local anesthetic* - By slowing absorption, epinephrine effectively **increases the duration of action** of the local anesthetic. - The anesthetic remains at the site of action for a longer period, providing **extended pain relief**. *Increases metabolism of local anesthetic* - Epinephrine does not directly affect the **metabolic rate** of local anesthetics. - The primary mechanism of metabolism for amides like lignocaine is in the **liver** by cytochrome P450 enzymes.
Question 485: Which anaesthetic agent is neither metabolised by liver nor by kidney?
- A. Vecuronium
- B. Pancuronium
- C. Rocuronium
- D. Atracurium (Correct Answer)
Explanation: ***Atracurium*** - **Atracurium** undergoes **Hofmann elimination**, a non-enzymatic chemical degradation in plasma, and also **ester hydrolysis** by non-specific plasma esterases [2]. - This unique metabolism makes its elimination largely independent of **liver** and **kidney function**, making it a good choice for patients with organ dysfunction [2]. *Vecuronium* - Primarily metabolized by the **liver** into active and inactive metabolites [1]. - Its elimination can be prolonged in patients with **hepatic impairment** [1]. *Pancuronium* - Undergoes significant **hepatic metabolism** and subsequent **renal excretion** of both parent drug and metabolites [1]. - Its duration of action is significantly affected by both **liver** and **kidney dysfunction** [1]. *Rocuronium* - Primarily eliminated unchanged via **biliary excretion** (liver) [1]. - Its duration of action is prolonged in patients with **hepatic impairment** [1].
Question 486: Which of the following statements about the biodisposition of penicillins and cephalosporins is NOT accurate?
- A. Procaine penicillin G is used for intramuscular injection
- B. Nafcillin and ceftriaxone are eliminated mainly by biliary secretion
- C. Oral bioavailability is affected by lability to gastric acid
- D. Renal tubular reabsorption of beta-lactams is inhibited by probenecid (Correct Answer)
Explanation: ***Renal tubular reabsorption of beta-lactams is inhibited by probenecid*** - Probenecid inhibits the **active tubular secretion** of beta-lactam antibiotics, not their reabsorption, thereby increasing their half-life and maintaining higher plasma concentrations [3]. - This interaction is clinically useful for prolonging the antibacterial effect of penicillins and cephalosporins. *Oral bioavailability is affected by lability to gastric acid* - Many early penicillins, such as **penicillin G**, are highly susceptible to degradation by stomach acid, leading to poor oral bioavailability [2]. - This necessitates their administration via intravenous or intramuscular routes, or the development of **acid-stable analogs** like penicillin V [2]. *Procaine penicillin G is used for intramuscular injection* - **Procaine penicillin G** is formulated for intramuscular injection to create a **depot effect**, allowing for slow absorption and prolonged therapeutic plasma concentrations. - The procaine component also acts as a **local anesthetic**, reducing the pain associated with a large-volume intramuscular injection [1]. *Nafcillin and ceftriaxone are eliminated mainly by biliary secretion* - **Nafcillin** and **ceftriaxone** are indeed notable among beta-lactam antibiotics for their significant elimination through the biliary tract. - This route of excretion makes them particularly useful in patients with **renal impairment**, as their elimination is less dependent on kidney function.
Question 487: Which of the following is not a phase I reaction?
- A. Oxidation
- B. Reduction
- C. Hydrolysis
- D. Conjugation (Correct Answer)
Explanation: ***Conjugation*** - **Conjugation** reactions are characteristic of **phase II metabolism**, where a polar molecule is added to the drug to increase its water solubility and facilitate excretion. - This process is distinct from phase I reactions which primarily involve exposure of functional groups. *Oxidation* - **Oxidation** is a primary **phase I metabolic reaction**, often mediated by cytochrome P450 enzymes. - It introduces or exposes a polar functional group on the drug molecule. *Reduction* - **Reduction** is another key **phase I metabolic reaction**, which involves the gain of electrons by a drug molecule. - This reaction can alter the drug's activity or prepare it for further metabolism. *Hydrolysis* - **Hydrolysis** is a **phase I metabolic reaction** that involves the cleavage of a chemical bond by water. - This process typically breaks down esters and amides, exposing functional groups.
Question 488: Neuromuscular blocker of choice in renal failure is:
- A. Atracurium (Correct Answer)
- B. Pancuronium
- C. Rocuronium
- D. Tubocurare
Explanation: ***Atracurium*** - **Atracurium** is metabolized by **Hofmann elimination** and ester hydrolysis, which are non-organ dependent metabolic pathways [2]. - This makes it a suitable choice in patients with **renal or hepatic impairment** as its clearance is not significantly affected by organ dysfunction. *Pancuronium* - **Pancuronium** is primarily eliminated via **renal excretion**, with approximately 80% of the unchanged drug excreted by the kidneys. - In patients with renal failure, its **duration of action is significantly prolonged**, increasing the risk of prolonged paralysis. *Rocuronium* - **Rocuronium** is predominantly eliminated by the **liver**, but a significant portion (10-20%) is also excreted unchanged by the kidneys [1]. - While generally considered safer than pancuronium in renal failure, its **duration of action can still be moderately prolonged** in severe renal impairment [1]. *Tubocurare* - **Tubocurare** is primarily eliminated via **renal excretion**, with a small amount also metabolized by the liver. - Its use has largely been superseded by newer neuromuscular blockers due to its **tendency to cause histamine release** and significant prolongation of action in renal failure [3].
Question 489: Which of the following best demonstrates the variability in drug responsiveness among individuals?
- A. Potency
- B. Quantal Dose Response Curve (Correct Answer)
- C. Efficacy
- D. Graded Dose Response Curve
Explanation: ***Quantal Dose Response Curve*** - A **quantal dose-response curve** plots the percentage of individuals exhibiting a discrete, all-or-none effect against the log dose of a drug. - This curve directly illustrates the **variability in drug responsiveness** within a population by showing the range of doses required to produce a specific effect in different individuals. *Efficacy* - **Efficacy** refers to the maximum effect a drug can produce, regardless of the dose. - While efficacy is an important pharmacological parameter, it describes the drug's overall therapeutic potential, not the **individual variability** in response. *Potency* - **Potency** is a measure of the amount of drug needed to produce an effect of given intensity. - It relates to the absolute dose required for a particular effect but does not directly demonstrate the **inter-individual differences** in biological response. *Graded Dose Response Curve* - A **graded dose-response curve** depicts the relationship between the dose of a drug and the **magnitude of the effect** in a **single biological unit** (e.g., an individual, a tissue, or a cell). - This curve reflects the relationship between drug concentration and effect intensity, but not the **variability in response among different individuals** in a population.
Question 490: Which muscle relaxant is primarily excreted by the kidneys?
- A. Vecuronium
- B. Pancuronium
- C. Gallamine (Correct Answer)
- D. Atracurium
Explanation: Everything in nature is balanced. ***Gallamine*** - **Gallamine** is predominantly cleared from the body through **renal excretion** (>90%), with very low hepatic metabolism. - Due to its high reliance on kidney function for elimination, **gallamine** is contraindicated in patients with **renal impairment**. [2] - **Note**: Gallamine has limited current clinical use and has been withdrawn from many markets, but remains important for understanding muscle relaxant pharmacokinetics. *Pancuronium* - **Pancuronium** has significant renal elimination (~40-50%), along with hepatic metabolism and biliary excretion. - While renal excretion is clinically important for **pancuronium** (making dose adjustment necessary in renal impairment), gallamine has a higher percentage of renal excretion. - Among **currently used** muscle relaxants, pancuronium shows the greatest dependence on renal function. *Vecuronium* - **Vecuronium** is mainly eliminated by **hepatic metabolism** (60-80%) and **biliary excretion**, with only a small fraction (10-25%) excreted renally. [1] - Its intermediate duration of action is attributed to rapid redistribution and hepatic metabolism, making it relatively safer for patients with renal dysfunction. [1] *Atracurium* - **Atracurium** undergoes unique elimination via **Hofmann degradation** (non-enzymatic chemical breakdown at physiological pH and temperature) and **ester hydrolysis**, independent of organ function. [3] - This makes it the preferred choice in patients with **renal** or **hepatic failure** as its metabolism does not rely on these organs. [3]
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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