Understanding the One-compartment open model with IV bolus administration is essential for B. Pharm students studying pharmacokinetics. This model assumes instantaneous distribution into a single, well-mixed compartment and monoexponential elimination described by the elimination rate constant (kel). Key concepts include calculation of initial concentration (C0), volume of distribution (Vd), half-life (t1/2), clearance (CL), AUC and concentration–time profiles using Ct = C0 e-kel t. Mastery of these principles helps with dose calculation, interpretation of Vd and CL, and log-linear plotting skills. These MCQs focus on theory, calculations, units, assumptions and clinical implications to strengthen your problem-solving. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which statement best describes the one-compartment open model after IV bolus administration?
- Instantaneous distribution into a single well-mixed compartment with monoexponential elimination
- Distribution into multiple tissue compartments with biexponential elimination
- Elimination follows zero-order kinetics regardless of concentration
- Drug remains entirely in the plasma without tissue distribution
Correct Answer: Instantaneous distribution into a single well-mixed compartment with monoexponential elimination
Q2. What is the correct expression for initial concentration (C0) immediately after an IV bolus in a one-compartment model?
- C0 = Dose × Vd
- C0 = Dose / Vd
- C0 = Dose / CL
- C0 = CL / Dose
Correct Answer: C0 = Dose / Vd
Q3. How is the elimination rate constant (kel) related to half-life (t1/2) in first-order kinetics?
- kel = t1/2 / 0.693
- kel = 0.693 × t1/2
- kel = 0.693 / t1/2
- kel = ln(t1/2)
Correct Answer: kel = 0.693 / t1/2
Q4. For an IV bolus one-compartment model, which equation gives the area under the plasma concentration–time curve (AUC)?
- AUC = C0 × kel
- AUC = Dose × Vd
- AUC = Dose / CL
- AUC = Vd / CL
Correct Answer: AUC = Dose / CL
Q5. Which relationship correctly links clearance (CL), volume of distribution (Vd) and elimination rate constant (kel)?
- CL = Vd / kel
- CL = Vd × kel
- CL = kel / Vd
- CL = Vd + kel
Correct Answer: CL = Vd × kel
Q6. On a semilogarithmic plot (ln concentration vs time) for a one-compartment IV bolus, what does the slope represent?
- Slope = +kel
- Slope = -kel
- Slope = CL
- Slope = Vd
Correct Answer: Slope = -kel
Q7. What are the usual units used for volume of distribution (Vd)?
- Mass (mg)
- Time (h)
- Liters (L) or liters per kg (L/kg)
- Concentration (mg/L)
Correct Answer: Liters (L) or liters per kg (L/kg)
Q8. What are common units for clearance (CL)?
- mg
- L/h or mL/min (volume per unit time)
- hour (h)
- unitless
Correct Answer: L/h or mL/min (volume per unit time)
Q9. Which equation describes plasma concentration at time t after an IV bolus in a one-compartment first-order model?
- Ct = C0 + kel × t
- Ct = C0 × e^(kel t)
- Ct = C0 × e^(-kel t)
- Ct = Dose / (Vd × kel)
Correct Answer: Ct = C0 × e^(-kel t)
Q10. When plotting ln(concentration) versus time and extrapolating the terminal line back to time zero, what is the intercept?
- The elimination rate constant kel
- The area under the curve (AUC)
- Extrapolated y-intercept equals C0 (initial concentration)
- The clearance value
Correct Answer: Extrapolated y-intercept equals C0 (initial concentration)
Q11. A straight line on a semilog concentration–time plot most directly indicates which type of elimination?
- Zero-order elimination
- First-order (single exponential) elimination
- Michaelis–Menten elimination
- No elimination (steady concentration)
Correct Answer: First-order (single exponential) elimination
Q12. In first-order elimination within a one-compartment model, how does half-life behave with changing dose?
- Half-life increases with dose
- Half-life decreases with dose
- Half-life is independent of dose
- Half-life becomes zero at high dose
Correct Answer: Half-life is independent of dose
Q13. A very large apparent Vd (much greater than total body water) typically suggests what about a drug?
- It is confined to plasma
- Extensive distribution into tissues or strong tissue binding
- Rapid renal excretion only
- Insufficient absorption from the gut
Correct Answer: Extensive distribution into tissues or strong tissue binding
Q14. If a drug has an apparent Vd smaller than plasma volume, what is the likely interpretation?
- The drug is highly lipophilic and accumulates in fat
- The drug is mainly confined to plasma, likely with high plasma protein binding
- The drug is primarily intracellular
- The drug has very rapid tissue distribution
Correct Answer: The drug is mainly confined to plasma, likely with high plasma protein binding
Q15. Which formula gives the loading dose needed to achieve a target plasma concentration immediately after an IV bolus?
- Loading dose = CL × Css
- Loading dose = Target concentration × Vd
- Loading dose = AUC × kel
- Loading dose = Vd / target concentration
Correct Answer: Loading dose = Target concentration × Vd
Q16. For continuous IV infusion, what is the maintenance infusion rate required to achieve a desired steady-state concentration (Css)?
- Rate = Vd × Css
- Rate = Kel × Vd
- Rate = CL × Css
- Rate = Dose / AUC
Correct Answer: Rate = CL × Css
Q17. Which equality holds true for AUC in a one-compartment IV bolus model with first-order elimination?
- AUC = C0 × kel
- AUC = C0 / kel = Dose / CL
- AUC = Vd / Dose
- AUC = kel / C0
Correct Answer: AUC = C0 / kel = Dose / CL
Q18. What is the standard practical method to estimate kel from concentration–time data?
- Plot concentration vs time on linear scale and measure intercept
- Plot ln(concentration) vs time and determine slope (slope = -kel)
- Integrate the curve numerically without transformation
- Measure time to reach peak concentration only
Correct Answer: Plot ln(concentration) vs time and determine slope (slope = -kel)
Q19. What is the absolute bioavailability (F) for an IV bolus dose?
- F = 0 (no bioavailability)
- F = 0.5 (50%)
- F = 1 (100%)
- F depends on hepatic extraction only
Correct Answer: F = 1 (100%)
Q20. How does doubling systemic clearance (CL) affect the AUC for the same IV bolus dose (assuming linear kinetics)?
- AUC doubles
- AUC remains unchanged
- AUC is halved
- AUC increases by fourfold
Correct Answer: AUC is halved
Q21. If elimination follows zero-order kinetics, what is the expected shape on a semilog concentration–time plot?
- A straight line
- A parabola
- A curve that is not linear (not a straight line)
- Vertical line
Correct Answer: A curve that is not linear (not a straight line)
Q22. How is C0 practically obtained when the earliest measured concentration is after some distribution or sampling delay?
- Use the highest observed concentration directly as C0
- Extrapolate the terminal log-linear phase back to time zero to estimate C0
- Calculate C0 as AUC × kel
- Assume C0 equals steady-state concentration
Correct Answer: Extrapolate the terminal log-linear phase back to time zero to estimate C0
Q23. Which equation allows calculation of clearance from a single IV bolus dose and measured AUC?
- CL = Dose × AUC
- CL = Dose / AUC
- CL = AUC / Dose
- CL = Dose × C0
Correct Answer: CL = Dose / AUC
Q24. Numerical relation: If a drug has t1/2 = 4 hours, what is kel (approx)?
- kel ≈ 0.173 h⁻¹
- kel ≈ 2.77 h⁻¹
- kel ≈ 0.693 h
- kel ≈ 4 h⁻¹
Correct Answer: kel ≈ 0.173 h⁻¹
Q25. How does high plasma protein binding typically affect apparent Vd?
- Increases Vd dramatically because protein-bound drug enters tissues easily
- Decreases apparent Vd because more drug remains in plasma bound to proteins
- Has no effect on Vd
- Changes Vd only if drug is renally excreted unchanged
Correct Answer: Decreases apparent Vd because more drug remains in plasma bound to proteins
Q26. To achieve a desired concentration Ct at a future time t after IV bolus, which equation gives the required bolus dose?
- Dose = Ct / Vd × e^(-kel t)
- Dose = Ct × Vd × e^(kel t)
- Dose = Ct × CL / kel
- Dose = Ct × AUC
Correct Answer: Dose = Ct × Vd × e^(kel t)
Q27. Which pharmacokinetic parameter depends on both Vd and CL?
- Clearance (CL) only depends on Vd
- Volume of distribution (Vd) only depends on CL
- Half-life (t1/2) depends on both Vd and CL
- AUC depends on Vd but not on CL
Correct Answer: Half-life (t1/2) depends on both Vd and CL
Q28. An observed apparent Vd ≈ 0.05 L/kg most likely corresponds to which distribution pattern?
- Predominantly intracellular distribution
- Extensive tissue binding, especially fat
- Mainly confined to plasma
- Extraordinarily high distribution into bone
Correct Answer: Mainly confined to plasma
Q29. Which formula is used to calculate apparent volume of distribution from a bolus dose and extrapolated C0?
- Vd = Dose × C0
- Vd = Dose / C0
- Vd = CL / kel
- Vd = AUC / Dose
Correct Answer: Vd = Dose / C0
Q30. In which clinical situation is the simple one-compartment IV bolus model likely inappropriate?
- When rapid equilibrium between plasma and tissues is achieved instantly
- When a distinct distribution (alpha) phase produces a biexponential decline (multi-compartment behavior)
- When elimination is strictly first-order and monoexponential
- When the drug is administered orally with complete absorption
Correct Answer: When a distinct distribution (alpha) phase produces a biexponential decline (multi-compartment behavior)
