Pharmacokinetics and Pharmacodynamics Practice Questions

Q: Which of the following is NOT an advantage of sustained release preparations over conventional preparations?

Drugs with very long half-life are suitable. ***Drugs with very long half-life are suitable*** - Sustained-release preparations are most suitable for drugs with a **half-life between 2 to 8 hours** (some sources suggest 3-12 hours). - Drugs with a **very long half-life (>12-24 hours)** are already long-acting enough that a sustained-release formulation offers **little to no additional benefit**. - Such drugs already maintain therapeutic levels for extended periods without the need for special formulation. - Formulating a drug with a very long half-life into a sustained-release form could lead to **excessive accumulation** and make dose adjustments difficult. - Therefore, suitability of drugs with very long half-life is **NOT an advantage** - it's actually a limitation of sustained-release technology. *Decreased frequency of administration* - This is a primary advantage of sustained release, as it allows for **less frequent dosing intervals** (e.g., once or twice daily instead of multiple times a day). - Reduced dosing frequency helps maintain **therapeutic drug levels** over a longer period without repeated administration. *Improved compliance* - Less frequent dosing directly contributes to **better patient adherence** to the medication regimen. - Patients are more likely to take their medication as prescribed when the **dosing schedule is simpler and less demanding**. *Less incidence of high peak side effects* - Sustained-release formulations provide a **slow and continuous drug release**, avoiding the rapid absorption and high plasma peaks seen with conventional formulations. - This smoother plasma concentration profile leads to **fewer dose-related side effects** associated with high peak drug concentrations.

Q: Most variable absorption is seen with which route?

Oral. ***Oral*** - **Oral absorption** is highly variable due to numerous factors, including stomach pH, presence of food, drug formulation, and individual patient differences in gastrointestinal motility and enzyme activity [1], [3]. - The drug must first dissolve and then pass through the **intestinal wall** into the bloodstream, where it is also subject to **first-pass metabolism** in the liver, all contributing to variability [2]. *Intramuscular* - While generally reliable, **intramuscular absorption** can vary depending on factors such as muscle blood flow, which can be influenced by activity, temperature, and depth of injection. - However, it bypasses the harsh gastrointestinal environment and has less intrinsic variability than oral administration. *Intravenous* - **Intravenous administration** provides the most direct and complete absorption, as the drug is introduced directly into the bloodstream, bypassing all absorption barriers. - Therefore, it exhibits **no variability in absorption** (bioavailability is 100%), making this option incorrect [4]. *Per rectal* - **Rectal absorption** can be variable, as it depends on factors like the drug's lipid solubility, the pH of the rectal fluid, and the presence of fecal matter. - However, it typically avoids **first-pass metabolism** to some extent and often provides more predictable absorption than oral routes, especially for drugs irritating to the stomach.

Q: Which of the following drug substrate combinations is incorrectly matched?

CYP 2C8/9 - mifepristone. ***CYP 2C8/9 - mifepristone*** - **Mifepristone** is primarily metabolized by **CYP 3A4**, not CYP 2C8/9. - CYP 2C8/9 metabolizes drugs like **warfarin**, rosiglitazone, and tolbutamide. *CYP 3A4/5 - simvastatin* - **Simvastatin** is a known substrate for **CYP 3A4/5**, and its metabolism can be significantly affected by CYP 3A4/5 inhibitors or inducers. - This interaction is clinically important for **drug-drug interactions** concerning statin therapy. *CYP 2D6 - SSRI* - Many **Selective Serotonin Reuptake Inhibitors (SSRIs)**, such as fluoxetine, paroxetine, and venlafaxine, are metabolized by **CYP 2D6**. - This makes CYP 2D6 a crucial enzyme in determining **SSRI efficacy** and **side effect profiles**. *CYP 2C19 - omeprazole* - **Omeprazole**, a proton pump inhibitor, is primarily metabolized by **CYP 2C19** and also by CYP 3A4. - Genetic polymorphisms in **CYP 2C19** can significantly affect omeprazole's metabolism and clinical efficacy.

Q: Refer to the graph showing three drugs A, B, and C. Which of the following drugs has the highest potency?

Drug A. ***Drug A*** - **Potency** refers to the amount of drug needed to produce a given effect; a drug with higher potency produces a greater effect at lower concentrations. - **Drug A** achieves its peak effect at the lowest concentration among the three, indicating it is the most potent. *Drug B* - **Drug B** reaches an intermediate peak effect at significantly higher concentrations compared to Drug A. - Its curve is shifted to the right of Drug A, indicating lower potency than Drug A. *Drug C* - **Drug C** requires the highest concentration to achieve its maximum effect, and also has the lowest maximum effect compared to Drugs A and B. - This indicates it has the lowest potency and efficacy of the three. *Both Drug A and B* - While both drugs exhibit efficacy, **Drug A** is distinctly more potent than Drug B, as it achieves its maximum effect at a much lower concentration. - Therefore, stating both have the highest potency is incorrect because Drug A is clearly superior in potency.

Q: A drug with high plasma protein binding property has which of the following properties?

Lower volume of distribution. ***Lower volume of distribution*** - Drugs with high plasma protein binding are largely confined to the **vascular compartment** as they bind to proteins (e.g., albumin, alpha-1-acid glycoprotein), making them less available to distribute into tissues. - This confinement within the plasma compartment results in a **smaller apparent volume of distribution**. *Less drug interaction* - High plasma protein binding actually increases the potential for **drug-drug interactions** through displacement. - If a second drug displaces the first from its binding sites, it can increase the **free fraction** and potentially lead to toxicity. *Reduced renal clearance* - While highly protein-bound drugs are generally not easily filtered by the glomeruli, their primary route of elimination is often through **hepatic metabolism** or **active tubular secretion**, rather than reduced renal elimination. - Many highly protein-bound drugs still undergo significant renal excretion via **active secretion**, if they are substrates for active transporters. *Less tubular secretion* - Plasma protein binding does not inherently reduce tubular secretion; in some cases, the drug-protein complex can dissociate rapidly at the secretory sites, allowing for efficient secretion of the **free drug**. - In fact, many drugs that undergo significant tubular secretion are also highly protein-bound, as protein binding helps **maintain a concentration gradient** for and delivery of the drug to the secretion transporters.

Q: At pKa = pH, what is the relationship between the ionic and non-ionic forms of a drug?

Conc. of drug is 50% ionic and 50% non-ionic. ***Conc. of drug is 50% ionic and 50% non-ionic*** - At **pKa = pH**, the concentrations of the **ionized** and **unionized** forms of a drug are equal as per the **Henderson-Hasselbalch equation**. - This means that exactly **half** of the drug molecules are in their charged (ionic) state, and the other half are in their uncharged (non-ionic) state. *Absorption of drug is 50% ionic and 50% non-ionic* - The amount of drug that is absorbed is dependent on the **non-ionic concentration** available at the absorption site, but this option incorrectly states that the *absorption itself* is 50% ionic. - Absorption primarily occurs for the **non-ionic, lipophilic form** as it can more readily cross cell membranes. *Conc. of drug is 75% ionic and 25% non-ionic* - This ratio would occur when the **pH** is either 0.5 units above the pKa for a weak acid or 0.5 units below the pKa for a weak base. - For example, if **pH = pKa + 0.5** (for a weak acid), approximately 75% would be ionic. *Conc. of drug is 25% ionic and 75% non-ionic* - This ratio would occur when the **pH** is either 0.5 units below the pKa for a weak acid or 0.5 units above the pKa for a weak base. - For example, if **pH = pKa - 0.5** (for a weak acid), approximately 25% would be ionic.

Q: Variation in sensitivity of response to different doses of a drug in different individuals is obtained from?

Dose-response relationship. ***Dose-response relationship*** - The **dose-response relationship** (particularly the **graded dose-response curve**) describes how the magnitude of a drug's effect changes with different doses. - When plotted for different individuals or populations, these curves reveal **variation in sensitivity** through differences in potency (horizontal shift) and efficacy (maximum response). - This relationship helps characterize inter-individual variability in drug response and is the fundamental concept for understanding differential sensitivity. *Therapeutic index* - The **therapeutic index** is a measure of drug safety, representing the ratio between the toxic dose and the effective dose (TD50/ED50 or LD50/ED50). - It does not directly explain the variation in sensitivity to different doses among individuals, but rather provides information about the drug's overall safety margin. *Bioavailability* - **Bioavailability** refers to the fraction of an administered drug that reaches the systemic circulation unchanged. - While it influences the drug concentration at the site of action, it doesn't directly measure the variability in physiological response to that concentration among individuals. *Phase 1 clinical trials* - **Phase 1 clinical trials** are the first stage of testing a new drug in humans, primarily focusing on safety, dosage range, and pharmacokinetics in a small group of healthy volunteers. - While variability in response may be observed during these trials, they are not the *pharmacological concept* that describes this variation; rather, dose-response relationships are used to interpret findings from these trials.

Q: High volume of distribution is primarily determined by:

High lipid solubility. ***High lipid solubility***- Highly **lipid-soluble** drugs readily cross biological membranes and distribute extensively into tissues, including adipose tissue, CNS, and intracellular compartments, leading to a **high volume of distribution (Vd)** [1, 2].- This property allows the drug to move out of the bloodstream and into various body compartments, increasing the apparent volume in which the drug is dissolved [1].*High plasma protein binding*- **High plasma protein binding** generally **restricts** drug distribution to tissues because only the **unbound (free) fraction** can diffuse across capillary membranes into interstitial fluid and cells [1].- This typically leads to a **lower Vd**, as the drug is largely retained within the plasma compartment.*Elimination rate*- The **elimination rate** determines how quickly the drug is removed from the body, affecting the **duration of action** rather than the extent of distribution.- It influences drug concentration changes over time but does not directly determine the physical space (volume) into which the drug distributes.*Half-life of the drug*- The **half-life (t½)** is the time required for drug concentration to reduce by half, and it is **determined by** both Vd and clearance (t½ = 0.693 × Vd/CL).- Half-life is a **consequence** of Vd and clearance, not a primary determinant of how widely a drug distributes [3].

Q: Which of the following drugs is NOT metabolized by acetylation?

Metoclopramide. ***Metoclopramide*** - **Metoclopramide** is eliminated primarily via renal excretion, with a smaller portion undergoing glucuronidation and sulfation, not acetylation. - Its metabolic pathway does not involve the enzyme **N-acetyltransferase**, which is responsible for acetylation. *Dapsone* - **Dapsone** undergoes significant **N-acetylation** by NAT2 (N-acetyltransferase 2), which is important for its metabolism and clearance. - Genetic variations in NAT2 can lead to individual differences in **dapsone acetylation rates**, affecting drug efficacy and toxicity. *Procainamide* - **Procainamide** is primarily metabolized by N-acetyltransferase 2 (NAT2) to **N-acetylprocainamide (NAPA)**, an active metabolite. - Differences in **acetylation phenotype** (slow vs. rapid acetylators) influence the metabolism of procainamide and the risk of drug-induced lupus. *INH* - **Isoniazid (INH)** is extensively metabolized in the liver, primarily by **N-acetylation** via the enzyme N-acetyltransferase 2 (NAT2). - The rate of INH acetylation varies significantly among individuals, classifying them as **slow or rapid acetylators**, which impacts drug toxicity and efficacy.

Question 1

Which of the following is NOT an advantage of sustained release preparations over conventional preparations?

Accepted Answer

Drugs with very long half-life are suitable

Answer

Improved compliance

Answer

Less incidence of high peak side effects

Answer

Decreased frequency of administration

Question 2

Most variable absorption is seen with which route?

Accepted Answer

Oral

Answer

Intravenous

Answer

Per rectal

Answer

Intramuscular

Question 3

Which of the following drug substrate combinations is incorrectly matched?

Accepted Answer

CYP 2C8/9 - mifepristone

Answer

CYP 3A4/5 - simvastatin

Answer

CYP 2D6 - SSRI

Answer

CYP 2C19 - omeprazole

Question 4

Refer to the graph showing three drugs A, B, and C. Which of the following drugs has the highest potency?

Accepted Answer

Drug A

Answer

Drug B

Answer

Drug C

Answer

Both Drug A and B

Question 5

A drug with high plasma protein binding property has which of the following properties?

Accepted Answer

Lower volume of distribution

Answer

Reduced renal clearance

Answer

Less drug interaction

Answer

Less tubular secretion

Question 6

At pKa = pH, what is the relationship between the ionic and non-ionic forms of a drug?

Accepted Answer

Conc. of drug is 50% ionic and 50% non-ionic

Answer

Absorption of drug is 50% ionic and 50% non-ionic

Answer

Conc. of drug is 25% ionic and 75% non-ionic

Answer

Conc. of drug is 75% ionic and 25% non-ionic

Question 7

Variation in sensitivity of response to different doses of a drug in different individuals is obtained from?

Accepted Answer

Dose-response relationship

Answer

Therapeutic index

Answer

Bioavailability

Answer

Phase 1 clinical trials

Question 8

High volume of distribution is primarily determined by:

Accepted Answer

High lipid solubility

Answer

High plasma protein binding

Answer

Elimination rate

Answer

Half-life of the drug

Question 9

Which statement best describes first-order kinetics in pharmacokinetics?

Accepted Answer

Elimination of the drug is proportional to the serum concentration

Answer

Absorption of the drug is independent of the serum concentration

Answer

Absorption of the drug is proportional to the serum concentration

Answer

Elimination of the drug is independent of the serum concentration

Question 10

Which of the following drugs is NOT metabolized by acetylation?

Accepted Answer

Metoclopramide

Answer

Dapsone

Answer

Procainamide

Answer

INH

Pharmacokinetics and Pharmacodynamics — MCQs

Pharmacokinetics and Pharmacodynamics — MCQs

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