Pharmacokinetics and Pharmacodynamics — MCQs

Pharmacokinetics and Pharmacodynamics Indian Medical PG Practice Questions and MCQs

Question 391: All of these fluids are isotonic except

A. 3% Normal saline (Correct Answer)
B. 5% dextrose
C. 0.9% Normal saline
D. Ringer lactate

Explanation: ***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 392: True statement about drug administration is

A. In the inhalational route, absorption of drugs takes place from vast surfaces of alveoli - so bioavailability is high and action is very rapid.
B. Irritation and local tissue necrosis can be seen in case of unsuitable routes like intramuscular or subcutaneous route.
C. sterile technique is needed in case of I.V. and I.M. administration. (Correct Answer)
D. 100% bioavailability is seen in case of IV route.

Explanation: ***Sterile technique is needed in case of I.V. and I.M. administration*** - **Sterile (aseptic) technique** is an absolute requirement for both intravenous (I.V.) and intramuscular (I.M.) drug administration to prevent **infectious complications** including local infection, abscess formation, and systemic sepsis. - This involves proper **skin disinfection**, use of **sterile needles and syringes**, and aseptic handling techniques. - This is a fundamental principle of safe parenteral drug administration emphasized in all pharmacology and clinical practice guidelines. *In the inhalational route, absorption of drugs takes place from vast surfaces of alveoli - so bioavailability is high and action is very rapid.* - This statement is **largely true** - the inhalational route does provide **rapid onset of action** due to the enormous surface area of alveoli (50-100 m²) and rich pulmonary capillary blood supply. - However, bioavailability via inhalation varies significantly (typically 10-60%) depending on particle size, inhalation technique, and formulation, unlike the more predictable parenteral routes. *Irritation and local tissue necrosis can be seen in case of unsuitable routes like intramuscular or subcutaneous route.* - While **irritation** can occur with certain drugs, **tissue necrosis** is a severe complication that occurs only with highly caustic substances (e.g., chemotherapeutic agents extravasation, concentrated potassium solutions) or severe injection errors. - This is not a general characteristic of IM or SC routes when used appropriately with suitable drugs. *100% bioavailability is seen in case of IV route.* - This statement is **true** - by definition, intravenous administration achieves **100% bioavailability** as the drug is placed directly into systemic circulation, bypassing all absorption barriers and first-pass metabolism. - However, in the context of this question asking for a "true statement about drug administration," the emphasis on sterile technique (Option 3) represents a more fundamental safety principle applicable to clinical practice.

Question 393: Elimination of alcohol follows

A. Zero order kinetics (Correct Answer)
B. Third Order kinetics
C. First order kinetics
D. Second order kinetics

Explanation: ***Zero order kinetics*** - Alcohol is metabolized at a **constant rate** (approximately 7-10 grams per hour) regardless of its concentration in the body. - This occurs because the metabolic enzymes like **alcohol dehydrogenase (ADH)** become **saturated** at blood alcohol concentrations typically achieved during drinking. - A **fixed amount** of alcohol is eliminated per unit of time, not a fixed percentage. - **Clinical significance**: This explains why you cannot speed up alcohol elimination by drinking coffee or taking cold showers. *Third Order kinetics* - This kinetic order is **not typically observed** for drug elimination in biological systems. - It would imply an extremely complex relationship between concentration and elimination rate that is not seen in clinical pharmacology. *First order kinetics* - Most drugs follow **first-order kinetics**, where a **constant fraction** (percentage) of the drug is eliminated per unit of time. - This occurs when enzyme systems are **not saturated**, which is **not the case** with alcohol at typical intoxicating doses. - At very low blood alcohol concentrations (below enzyme saturation), alcohol may exhibit first-order kinetics. *Second order kinetics* - **Second-order kinetics** means the elimination rate is proportional to the **square of the drug concentration**. - This type of kinetics is **rarely relevant** for drug elimination in pharmacology.

Question 394: Alkalinization of urine is done in the management of poisoning with:

A. Morphine
B. Aspirin (Correct Answer)
C. Amphetamine
D. Atropine

Explanation: ***Aspirin*** - Alkalinization of urine is done in **aspirin overdose** to promote the **excretion of salicylic acid**, which is acidic. - By increasing the urine pH, more of the acidic aspirin metabolites become **ionized**, reducing their reabsorption in the renal tubules and increasing their elimination. *Morphine* - Morphine elimination is primarily through **hepatic metabolism** (glucuronidation) and subsequent renal excretion of inactive metabolites. - Urinary pH manipulation has **little impact** on its clearance. *Amphetamine* - Amphetamine is a **weak base**, and its excretion is enhanced by **acidification of urine**. - Alkalinization of urine would **increase reabsorption** and reduce its elimination, which is the opposite of what is desired in toxicity. *Atropine* - Atropine is primarily eliminated through **hepatic metabolism and renal excretion** of both unchanged drug and metabolites. - Manipulation of urinary pH has **minimal clinical utility** in enhancing its elimination.

Question 395: Corticosteroid which needs least systemic monitoring is:

A. Dexamethasone
B. Budesonide (Correct Answer)
C. Prednisolone
D. Hydrocortisone

Explanation: ***Budesonide*** - This **corticosteroid** has a very high **first-pass metabolism** in the liver, leading to low systemic bioavailability. - Due to its localized action and minimal systemic exposure, it requires the **least systemic monitoring** compared to other corticosteroids. *Dexamethasone* - Has a **long half-life** and potent **glucocorticoid activity**, leading to significant systemic effects. - Requires careful monitoring for side effects like **hyperglycemia**, osteoporosis, and immune suppression. *Prednisolone* - A commonly used oral corticosteroid with **intermediate systemic potency** and half-life. - Requires monitoring for a range of systemic side effects, including **adrenal suppression** and fluid retention. *Hydrocortisone* - This is a short-acting corticosteroid, and its systemic use can lead to **significant mineralocorticoid effects** in addition to glucocorticoid effects. - Requires monitoring for electrolyte imbalances, **hypertension**, and other systemic corticosteroid side effects.

Question 396: Which of the following is the shortest acting benzodiazepine?

A. Midazolam (Correct Answer)
B. Alprazolam
C. Chlordiazepoxide
D. Diazepam

Explanation: ***Midazolam*** - **Midazolam** has a very short half-life (1.5-2.5 hours) and undergoes rapid metabolism, making it suitable for procedures needing **brief sedation** or inducing anesthesia. - Its quick onset and offset are due to its high lipid solubility and hepatic metabolism, leading to its prevalent use in **surgical and diagnostic settings**. *Alprazolam* - **Alprazolam** has an intermediate half-life (6-20 hours) and is commonly used for **anxiety disorders** and panic attacks. - While relatively fast-acting, its duration of action is significantly longer than Midazolam. *Chlordiazepoxide* - **Chlordiazepoxide** is a long-acting benzodiazepine with a half-life ranging from 5 to 30 hours, and its active metabolites can extend its effects even further. - It is often used for **alcohol withdrawal syndrome** and generalized anxiety. *Diazepam* - **Diazepam** is a long-acting benzodiazepine with a half-life of 20-100 hours, and its active metabolites (like desmethyldiazepam) have even longer half-lives. - It is used for conditions like **anxiety, muscle spasms, and seizures**, requiring prolonged therapeutic effects.

Question 397: Laudanosine is a toxic metabolite of?

A. Mivacurium
B. Atracurium (Correct Answer)
C. Vecuronium
D. Pancuronium

Explanation: ***Atracurium*** - Atracurium undergoes **Hofmann elimination**, a non-enzymatic degradation process, which produces **laudanosine** as a metabolite. - **Laudanosine** can accumulate, particularly in patients with renal or hepatic dysfunction, and at high concentrations, it may cause **CNS excitation** and seizures. *Mivacurium* - Mivacurium is rapidly metabolized by **plasma pseudocholinesterase**, an enzyme also responsible for the breakdown of succinylcholine. - Its breakdown products do not include laudanosine, and it has a relatively **short duration of action** due to this rapid metabolism. *Vecuronium* - Vecuronium is primarily eliminated by the **liver** and, to a lesser extent, the kidneys, with metabolites having some neuromuscular blocking activity. - It does not undergo Hofmann elimination and therefore does not produce laudanosine as a metabolite. *Pancuronium* - Pancuronium is primarily eliminated by the **kidneys**, with a significant portion excreted unchanged. - It is a long-acting neuromuscular blocker and does not produce laudanosine as a metabolite.

Question 398: In noncompetitive antagonism, the true statement is:

A. Km value increased; Vmax increased
B. Vmax decreased; Km value normal (Correct Answer)
C. No change in Vmax; Km value decrease
D. Km value decrease; Vmax decreases

Explanation: ***Vmax decreased; Km value normal*** - In **noncompetitive antagonism**, the antagonist binds to an **allosteric site** on the enzyme, altering its conformation and reducing its efficacy regardless of substrate concentration. - This results in a **reduced maximum velocity (Vmax)** because the antagonist effectively removes some enzyme molecules from participating in catalysis, but the **affinity (Km)** of the remaining active sites for the substrate is unaffected. *Km value increased; Vmax increased* - An **increased Km value** indicates a **decreased affinity** of the enzyme for its substrate, while an **increased Vmax** implies **enhanced catalytic activity**, which is not characteristic of any type of antagonism. - This pattern would suggest an enzyme that has been modified to bind less effectively but process substrate more rapidly, which is biologically uncommon in antagonism. *No change in Vmax; Km value decrease* - A **decreased Km value** signifies an **increased affinity** of the enzyme for its substrate, meaning it takes less substrate to reach half of the maximum velocity. - No change in Vmax combined with a decreased Km value is characteristic of **reversible competitive inhibition** at high substrate concentrations, not noncompetitive antagonism. *Km value decrease; Vmax decreases* - A **decreased Km value** suggests an **increased affinity**, meaning the enzyme binds more tightly to the substrate. - This combination is not typical for an antagonist; a reduced Vmax without a change in Km is characteristic of noncompetitive antagonism, while a decreased Km would imply improved binding.

Question 399: Among atracurium and cisatracurium, which of the following does not require dose modification in patients with renal or hepatic failure?

A. Both atracurium and cisatracurium (Correct Answer)
B. Cisatracurium
C. Atracurium
D. Neither atracurium nor cisatracurium

Explanation: ***Both atracurium and cisatracurium*** - Both **atracurium** and **cisatracurium** are metabolized primarily via **Hofmann elimination**, a non-enzymatic chemical degradation. - This mechanism is independent of renal or hepatic function, making them safe choices for patients with organ failure without requiring dose adjustment. *Cisatracurium* - While **cisatracurium** is known for its metabolism via **Hofmann elimination**, excluding atracurium from this category is incorrect. - Atracurium also undergoes significant Hofmann elimination, sharing this characteristic for organ-independent metabolism. *Atracurium* - While **atracurium** is metabolized via **Hofmann elimination**, excluding cisatracurium is incorrect, as cisatracurium also primarily utilizes this pathway. - Both agents are advantageous in patients with renal or hepatic impairment. *Neither atracurium nor cisatracurium* - This statement is incorrect because both drugs demonstrate metabolism independent of renal or hepatic function, which is a key advantage. - Their primary degradation pathway, **Hofmann elimination**, ensures that their elimination is not significantly affected by organ dysfunction.

Question 400: A patient presents with nephrotic syndrome and hypoalbuminemia. Protein binding of which drug is not affected?

A. Valproate
B. Morphine (Correct Answer)
C. Diazepam
D. Tolbutamide

Explanation: ***Morphine*** - Morphine is a **low protein-bound drug** (<35%), meaning a significant portion circulates freely. - Therefore, even with **reduced albumin levels** in nephrotic syndrome, the free fraction available for action is not significantly altered. *Valproate* - Valproate is **highly protein-bound** (90-95%), primarily to albumin. - In conditions like nephrotic syndrome with **hypoalbuminemia**, a decreased binding capacity leads to a higher free drug fraction and increased pharmacological effect. *Diazepam* - Diazepam is also **highly protein-bound** (98%), mainly to albumin. - Like other highly bound drugs, **hypoalbuminemia** in nephrotic syndrome would increase its free fraction, potentially leading to increased side effects. *Tolbutamide* - Tolbutamide is another drug with **high protein binding** (>90%), predominantly to albumin. - Reduced albumin levels in nephrotic syndrome would result in a **higher free concentration** of tolbutamide, increasing its hypoglycemic effect and risk of adverse reactions.

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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