Pharmacokinetics and Pharmacodynamics MCQs

Pharmacology · 113 free questions with answers & explanations.

1. A patient with severe hepatic cirrhosis (Child-Pugh Class C) is prescribed propranolol for portal hypertension. The dose must be reduced substantially. Which pharmacokinetic parameter most importantly explains propranolol's substantially increased bioavailability in cirrhosis?
2. A drug has a volume of distribution (Vd) of 500 L in a 70 kg adult. This large Vd most likely indicates:
3. A drug follows zero-order kinetics at therapeutic doses. Which clinical implication is most important?
4. A drug has a volume of distribution (Vd) of 420 L in a 70 kg patient. What does this imply about its distribution and plasma protein binding?
5. First-pass metabolism substantially reduces oral bioavailability of some drugs. Which cytochrome P450 enzyme is predominantly responsible for first-pass metabolism in the gut wall (not just liver) of drugs like cyclosporine and midazolam?
6. A drug has a volume of distribution (Vd) of 700 L. What does this pharmacokinetic parameter indicate about the drug's distribution?
7. The concept of 'therapeutic index' (TI) is not simply a ratio but reflects different pharmacokinetic-pharmacodynamic considerations depending on the drug's concentration-response curve. For a drug with a STEEP concentration-effect curve, a narrow TI is MOST concerning because:
8. A clinical pharmacologist analyses the pharmacokinetics of a new drug. At steady state, plasma concentration fluctuates between a peak of 20 mg/L and a trough of 5 mg/L with 12-hourly dosing. The drug's therapeutic index is defined by an MEC of 4 mg/L and MTC of 25 mg/L. What percentage of the dosing interval does the drug concentration remain within the therapeutic range?
9. A drug demonstrates 'saturation kinetics' at therapeutic plasma concentrations. A patient is stabilized on phenytoin 300 mg/day with a plasma level of 12 mg/L. The dose is increased by only 50 mg/day to 350 mg/day. Two weeks later, the patient presents with diplopia, ataxia, and nystagmus. Plasma phenytoin level is 38 mg/L. What explains this disproportionate rise?
10. A drug has a volume of distribution of 700 L in a 70 kg patient. This implies that the drug is:
11. The pharmacodynamic concept of 'spare receptors' (receptor reserve) explains which clinical phenomenon BEST?
12. A drug with a narrow therapeutic index is being dosed in a patient who develops acute renal failure. The pharmacokinetic parameter that MOST directly determines the accumulation and toxicity risk is:
13. A drug with Michaelis-Menten (zero-order at therapeutic doses) kinetics shows disproportionate toxicity when the dose is increased by 20%. This is because at saturation kinetics:
14. In pharmacogenomics, the concept of 'phenoconversion' differs from genotyping in predicting drug metabolism. Phenoconversion refers to:
15. A patient with severe renal impairment (eGFR 10 mL/min) is prescribed a drug that is 40% renally excreted as unchanged drug and 60% hepatically metabolised. The approximate dose adjustment required is:
16. Physiologically based pharmacokinetic (PBPK) modelling considers hepatic drug extraction. A drug with a high extraction ratio (E > 0.7) given orally would have which set of pharmacokinetic characteristics?
17. Phenytoin displays zero-order (saturation) kinetics at therapeutic doses. A patient at 300mg/day has a plasma level of 10 mcg/mL. When the dose is increased to 350mg/day, the plasma level rises to 25 mcg/mL rather than the expected 11.7 mcg/mL. This non-linear behavior is explained by:
18. A drug with high hepatic extraction ratio (ER > 0.7) is administered orally. Its oral bioavailability is determined primarily by:
19. A drug shows a shift in its concentration-response curve to the right with no change in maximum effect (Emax) in the presence of a second compound. Which type of antagonism is demonstrated?
20. A patient with hepatic cirrhosis (Child-Pugh B) requires an analgesic. Which pharmacokinetic parameter is most critically affected, and what adjustment principle should guide dosing?
21. Warfarin is a narrow therapeutic index drug where CYP2C9 genotype significantly affects dose requirement. Compared to CYP2C9*1/*1 (wild-type extensive metabolisers), CYP2C9*2/*3 patients require approximately 50–70% lower warfarin doses. What additional pharmacogenomic factor is co-considered in warfarin dosing algorithms (e.g., IWPC algorithm)?
22. A drug with a volume of distribution of 500 L and elimination half-life of 40 hours is given as a continuous IV infusion. Approximately how long does it take to reach 90% of steady-state plasma concentration?
23. A drug follows two-compartment pharmacokinetics. After IV bolus, the drug's plasma concentration-time curve shows a rapid initial decline (alpha/distribution phase) followed by a slower decline (beta/elimination phase). Which parameter is most useful for calculating the loading dose for this drug?
24. A patient is receiving vancomycin with an AUC/MIC-guided dosing strategy. The AUC0-24/MIC target for MRSA bacteremia is 400–600 mg·h/L. Compared to trough-only monitoring, AUC/MIC-guided dosing reduces which complication?
25. Mechanism-based inhibition (MBI) of CYP enzymes, as seen with erythromycin and CYP3A4, differs from competitive inhibition in its clinical consequences. What is the defining characteristic of MBI?
26. A drug has a volume of distribution (Vd) of 700 L in a 70 kg adult. This large Vd implies that:
27. Mechanism-based (suicide) inhibition of CYP enzymes is clinically important because it differs from competitive inhibition in that:
28. A patient requires a loading dose of digoxin to achieve rapid therapeutic plasma levels. The loading dose is calculated primarily based on:
29. A drug has a volume of distribution (Vd) of 400 L in a 70 kg patient. What does this signify about the drug's distribution, and what are the implications for dialysis in overdose?
30. Meropenem is used as a continuous infusion (not bolus) in critically ill patients with Pseudomonas bacteremia. The pharmacodynamic rationale is:
31. A drug has a volume of distribution (Vd) of 500 L in a 70 kg adult. Which pharmacokinetic conclusion is most accurate about this drug?
32. A drug follows two-compartment pharmacokinetics. After IV bolus, a biphasic plasma concentration decline is observed. The rapid initial decline (alpha phase) represents:
33. A drug has a narrow therapeutic index and is 95% protein bound. A co-administered drug displaces it from albumin, reducing binding to 90%. What is the expected change in free drug fraction and clinical significance?
34. A patient is a CYP2D6 ultrarapid metabolizer (URM) prescribed codeine for pain. What pharmacogenomic risk does this create?
35. A drug has a volume of distribution (Vd) of 400 L in a 70 kg adult. This finding most likely indicates:
36. CYP2C19 poor metabolisers (PMs) on clopidogrel therapy have significantly higher rates of adverse cardiovascular events compared to extensive metabolisers (EMs) because:
37. A loading dose is administered to achieve immediate therapeutic plasma concentration. The volume of distribution (Vd) is the primary pharmacokinetic parameter used to calculate the loading dose. This is because Vd reflects:
38. Phenytoin exhibits zero-order (saturation) kinetics at therapeutic doses. The clinical implication is:
39. The pharmacokinetic principle behind the clinical decision to administer vancomycin as an extended infusion (over 4 hours) rather than the traditional 1-hour infusion for resistant gram-positive infections is based on:
40. Which pharmacokinetic parameter is MOST relevant for calculating the loading dose of a drug, and what is its significance?
41. A drug is given intravenously at a loading dose of 100 mg. At steady state, the plasma concentration is measured as 2 mg/L. The volume of distribution (Vd) is:
42. A drug has a half-life of 6 hours and is given every 6 hours (one half-life interval). After how many doses will steady-state plasma concentration be approximately achieved?
43. Drug A has an intrinsic efficacy of 0.5 at a receptor (it is a partial agonist) and Drug B is a full agonist with intrinsic efficacy of 1.0. If both have equal receptor affinity and both are given together at saturating concentrations, the expected outcome is:
44. A drug undergoing zero-order (saturation) kinetics has a plasma concentration of 40 mg/L at time 0 and 30 mg/L at 2 hours. What will the plasma concentration be at 4 hours?
45. A patient with hepatic cirrhosis (Child-Pugh C) requires analgesic dosing adjustment. Which opioid requires the LEAST dose modification due to minimal hepatic first-pass metabolism and primary renal excretion?
46. Narrow therapeutic index drugs like phenytoin and warfarin show non-linear (Michaelis-Menten) pharmacokinetics at therapeutic concentrations. The clinical consequence is:
47. A drug has a volume of distribution (Vd) of 350 L and a plasma half-life of 20 hours. The total body clearance (CL) can be calculated as: CL = (0.693 × Vd) / t1/2. What is the clearance in mL/min?
48. In a drug with first-order kinetics, if the initial plasma concentration is 200 mg/L and the half-life is 6 hours, what is the plasma concentration after 18 hours?
49. A drug has zero-order kinetics at therapeutic doses. Which statement best describes the clinical implication?
50. The hepatic extraction ratio of lidocaine is 0.7 (high). Lidocaine is given orally to a patient. Its bioavailability will be approximately:
51. Which term describes the phenomenon where a drug's therapeutic effect diminishes with repeated dosing at the same dose, requiring increased doses for the same effect, due to receptor downregulation?
52. A drug has a volume of distribution (Vd) of 700 L in a 70 kg patient and a plasma half-life of 30 hours. Calculate the clearance of this drug. (Cl = 0.693 × Vd / t½)
53. A drug with a bioavailability of 40% and a clearance of 5 L/h is administered orally at 100 mg every 8 hours (τ = 8 h) at steady state. What is the average steady-state plasma concentration (Css,avg)?
54. Phenytoin exhibits Michaelis-Menten (zero-order/saturable/nonlinear) kinetics at therapeutic concentrations. The clinical consequence is:
55. In a two-compartment pharmacokinetic model after IV bolus dosing, the initial rapid decline in plasma concentration (alpha phase) represents:
56. A drug has a hepatic extraction ratio (E) of 0.9. Its oral bioavailability will be approximately:
57. A drug has a volume of distribution (Vd) of 350 L and a clearance of 35 L/h. Calculate its elimination half-life.
58. A patient receives a drug at a constant IV infusion rate (R0) of 50 mg/h. Its clearance is 10 L/h. Assuming first-order elimination, what is the steady-state plasma concentration (Css)?
59. A drug is given orally at 200 mg. Absolute bioavailability is 50%. Plasma protein binding is 90%. If the apparent volume of distribution is 20 L, what is the amount of drug distributed in the plasma compartment (assuming plasma volume ~3 L) versus tissues?
60. The Michaelis-Menten kinetics of phenytoin mean that it shows zero-order kinetics at therapeutic concentrations. What is the clinical implication of this saturation pharmacokinetics?
61. Which statement correctly defines the 'therapeutic index' (TI) and its clinical relevance?
62. A drug with first-order kinetics has a half-life of 6 hours. Approximately what fraction of the initial dose remains in the body after 24 hours?
63. A drug has a volume of distribution (Vd) of 700 L in a 70 kg patient and a clearance of 7 L/hour. What is its elimination half-life?
64. The therapeutic index (TI) of a drug is defined as the ratio of TD50 to ED50. A drug with a narrow therapeutic index requires:
65. An enzyme inducer such as rifampicin reduces plasma concentrations of concurrently administered drugs by which mechanism?
66. A new drug has a volume of distribution of 3.5 L/kg and a clearance of 1.75 L/hr/kg. In a 70-kg patient, what is the elimination half-life? [Vd = 3.5 L/kg × 70 kg = 245 L; CL = 1.75 L/hr/kg × 70 kg = 122.5 L/hr; t½ = 0.693 × Vd/CL]
67. A drug with zero-order kinetics is administered at 100 mg/hr by IV infusion. At steady state the plasma concentration is 50 mg/L. If the infusion rate is doubled to 200 mg/hr, what will be the new steady-state plasma concentration?
68. A drug has bioavailability of 40% after oral dosing due to first-pass hepatic metabolism. If the hepatic extraction ratio (ER) is 0.6 and the drug shows linear kinetics, what fraction of the oral dose actually reaches systemic circulation?
69. A drug is being administered by IV infusion at a rate of 60 mg/hr. Its half-life is 4 hours and volume of distribution is 20 L. What is the steady-state plasma concentration (Css)?
70. Drug A has an EC50 of 2 mg/L and a maximum effect (Emax) of 80 units. Drug B has an EC50 of 8 mg/L and an Emax of 80 units. Both are agonists at the same receptor. Which statement correctly characterizes the relationship between these drugs?
71. A drug has a volume of distribution (Vd) of 700 litres and a hepatic clearance of 35 L/hour. Calculate its elimination half-life.
72. A drug with 80% oral bioavailability is given 100 mg every 8 hours. Its total clearance is 450 mL/hour. What is the approximate average steady-state plasma concentration (Css,avg)?
73. A drug with a volume of distribution of 200 L and a clearance of 50 L/h is given as a single IV bolus dose. Calculate the half-life of this drug.
74. A drug that follows first-order kinetics has a half-life of 6 hours. A patient receives a continuous IV infusion starting at t=0. What is the approximate time required to reach 90% of steady-state plasma concentration?
75. The therapeutic index (TI) of a drug is defined as TD50/ED50. A drug with a TI of 2 compared to one with a TI of 100 means:
76. A drug is 80% orally bioavailable, primarily due to hepatic first-pass metabolism. After IV administration, its apparent volume of distribution is 50 L (body weight 70 kg). After an oral dose achieving steady-state, the drug's Vd is most accurately described as:
77. A drug has a volume of distribution (Vd) of 200 L in a 70-kg adult. Which statement about this drug is most likely correct?
78. A drug is administered as a 400 mg loading dose and has a Vd of 40 L. What is the expected initial plasma concentration (C0)?
79. Drug X has a half-life of 8 hours and is given every 8 hours (one half-life interval). Approximately how many doses are required to reach steady-state plasma concentrations?
80. Which of the following correctly describes the phenomenon of 'first-pass metabolism' and its clinical implication?
81. A drug is given as an IV bolus of 400 mg. Plasma concentration immediately after injection is 8 mg/L. Calculate the apparent volume of distribution (Vd) and select the correct option.
82. A drug has a half-life of 4 hours and is administered every 4 hours (one half-life interval). Assuming first-order kinetics and 100% bioavailability, at what fraction of the steady-state concentration will the drug be after 3 doses (12 hours)?
83. A drug has clearance (CL) of 10 L/hour and a volume of distribution (Vd) of 70 L. Calculate the elimination half-life.
84. The concept of 'therapeutic window' relates to the relationship between the minimum effective concentration (MEC) and minimum toxic concentration (MTC). Which pharmacodynamic concept is defined as the ratio of MTC to MEC?
85. A drug undergoes extensive first-pass metabolism in the liver. Its oral bioavailability is 20% despite complete GI absorption. The hepatic extraction ratio (ER) is:
86. A drug has a volume of distribution (Vd) of 150 L and a clearance of 3 L/hour. What is the elimination half-life?
87. A drug with zero-order kinetics and a rate of elimination of 50 mg/hour is given at 600 mg IV bolus. How many hours will it take to reach zero plasma concentration?
88. A competitive antagonist shifts the agonist dose-response curve. Which statement CORRECTLY describes this shift?
89. A drug undergoes extensive first-pass metabolism in the liver. If hepatic extraction ratio (EH) = 0.90, what is the approximate oral bioavailability?
90. A drug is administered as a 600 mg IV bolus. At time zero, the plasma concentration measured by back-extrapolation is 12 mg/L. The volume of distribution (Vd) of this drug is:
91. A drug has a volume of distribution of 40 L and an elimination half-life of 8 hours. Its clearance (in L/h) is approximately:
92. The Emax model of pharmacodynamics describes the relationship between drug concentration and effect. At what drug concentration is 50% of the maximum effect (Emax) achieved?
93. A drug has a volume of distribution of 50 L, a clearance of 5 L/hour, and is administered as a 100 mg IV bolus. What is the half-life of this drug?
94. Phenytoin exhibits zero-order (saturation) kinetics at therapeutic plasma concentrations. The clinical implication of this is:
95. A drug has a volume of distribution of 40 L and a clearance of 8 L/h. What is its elimination half-life?
96. A drug is administered as a constant IV infusion. It has a clearance of 5 L/h and a target steady-state concentration of 2 mg/L. What infusion rate is required to maintain this concentration?
97. A drug with a volume of distribution of 42 L is administered as an intravenous bolus. Its plasma clearance is 70 mL/min. The steady-state plasma concentration (Css) during a continuous infusion at 14 mg/hr is closest to:
98. A drug has a volume of distribution of 14 L and a clearance of 28 mL/min in a 70-kg patient. The elimination half-life is closest to:
99. The phenomenon of 'zero-order kinetics' in phenytoin toxicity occurs because:
100. Competitive antagonism can be distinguished from non-competitive (irreversible) antagonism on a log-dose-response curve by the fact that:
101. A drug has a volume of distribution of 70 L and a clearance of 7 L/hour. What is its elimination half-life?
102. A drug is given IV at a rate of 20 mg/hour. Its clearance is 5 L/hour. What is the expected steady-state plasma concentration (Css)?
103. An agonist produces 50% maximal response at a concentration of 10 nM (EC50). A competitive antagonist at 100 nM shifts the dose-response curve to the right, and the EC50 for the agonist increases to 100 nM. The apparent affinity (Ki) of the antagonist is closest to:
104. Phenytoin follows zero-order kinetics at therapeutic doses because its metabolism saturates hepatic enzymes. The clinical implication is:
105. The 'first-pass effect' explains why oral morphine requires higher doses than IV morphine for equivalent analgesia. For a drug with oral bioavailability of 25%, to achieve the same systemic exposure as 10 mg IV, the oral dose required is:
106. A drug has a volume of distribution of 40 L, a clearance of 10 L/h, and is administered as an IV bolus of 200 mg. What is its elimination half-life?
107. A patient with severe hepatic cirrhosis is prescribed a drug that undergoes 95% first-pass hepatic extraction. How will cirrhosis most likely affect its oral bioavailability?
108. Which statement correctly describes the concept of therapeutic index (TI) and its clinical implication?
109. A drug is 90% protein-bound in plasma. It is displaced from albumin by a second drug, increasing the free fraction from 10% to 20%. Assuming rapid redistribution and normal elimination, the new steady-state free-drug concentration compared to baseline would be:
110. Which statement best describes a partial agonist at a receptor?
111. A drug is administered as a 500 mg IV bolus and achieves an initial plasma concentration of 10 mg/L. Calculate the volume of distribution.
112. A drug undergoes zero-order (saturable) kinetics when plasma concentrations exceed a threshold. Which clinical consequence distinguishes zero-order from first-order pharmacokinetics?
113. Phenytoin has a narrow therapeutic index and exhibits capacity-limited (Michaelis-Menten) pharmacokinetics. At concentrations approaching therapeutic range (10-20 mg/L), which is the most appropriate clinical guidance for dose adjustments?