Calculation of loading dose MCQs With Answer

Introduction

This set of MCQs is designed for M.Pharm students to strengthen understanding of loading dose calculation within Clinical Pharmacokinetics and Therapeutic Drug Monitoring. It covers fundamental formulas, unit handling, bioavailability and salt factors, weight-based calculations, and practical clinical scenarios where a loading dose is required. Questions mix conceptual reasoning and numerical problems to build competence in determining the correct amount to rapidly achieve target plasma concentrations. Emphasis is placed on the role of volume of distribution, how bioavailability alters oral loading doses, the independence of loading dose from clearance, and adjustment strategies for protein binding or salt form. Use these items for revision or self-assessment.

Q1. Which of the following is the standard formula to calculate an intravenous loading dose to achieve a desired steady-state plasma concentration?

• Loading dose = (Desired plasma concentration × Clearance) / Bioavailability
• Loading dose = (Desired plasma concentration × Volume of distribution) / Bioavailability
• Loading dose = (Desired plasma concentration × Half‑life) / Bioavailability
• Loading dose = (Desired plasma concentration × Volume of distribution × Clearance)

Correct Answer: Loading dose = (Desired plasma concentration × Volume of distribution) / Bioavailability

Q2. If Vd is expressed in L/kg and the patient weight is known, which expression correctly gives the loading dose for an oral drug?

• Loading dose = Desired Cp × Vd(L/kg) / (Weight × F)
• Loading dose = Desired Cp × Vd(L/kg) × Weight × F
• Loading dose = Desired Cp × Vd(L/kg) × Weight / F
• Loading dose = Desired Cp × Weight / (Vd(L/kg) × F)

Correct Answer: Loading dose = Desired Cp × Vd(L/kg) × Weight / F

Q3. Which pharmacokinetic parameter does NOT determine the magnitude of an appropriate loading dose when targeting a given plasma concentration?

• Volume of distribution
• Desired plasma concentration
• Bioavailability
• Clearance

Correct Answer: Clearance

Q4. For an oral drug with low bioavailability, what is the primary implication for the loading dose compared with IV administration?

• The oral loading dose must be decreased proportionally to the lower bioavailability
• The oral loading dose must be increased to compensate for lower bioavailability
• Bioavailability does not affect loading dose; only Vd matters
• Oral loading doses are always the same as IV if given over the same time

Correct Answer: The oral loading dose must be increased to compensate for lower bioavailability

Q5. Calculate the IV loading dose for a 70 kg patient when Vd = 0.6 L/kg and desired plasma concentration is 8 mg/L (F = 1).

• 168 mg
• 336 mg
• 672 mg
• 48 mg

Correct Answer: 336 mg

Q6. Using the same parameters as Q5 but with oral bioavailability F = 0.5, what is the required oral loading dose?

• 168 mg
• 336 mg
• 672 mg
• 1344 mg

Correct Answer: 672 mg

Q7. When a drug is supplied as a salt and the salt factor (S) is 0.75, how should the loading dose formula be modified to give the amount of salt to administer?

• Loading dose(salt) = (Desired Cp × Vd) × F × S
• Loading dose(salt) = (Desired Cp × Vd) / (F × S)
• Loading dose(salt) = (Desired Cp × Vd) × (F / S)
• Salt factor does not influence loading dose calculation

Correct Answer: Loading dose(salt) = (Desired Cp × Vd) / (F × S)

Q8. Without a loading dose, approximately how long does it take for a continuous infusion to reach near steady state?

• About one half‑life
• About 4–5 half‑lives
• A few minutes regardless of half‑life
• It reaches steady state immediately

Correct Answer: About 4–5 half‑lives

Q9. Calculate the loading dose for a drug with Vd = 40 L, desired concentration 10 mg/L, and oral bioavailability F = 0.8 (dose given orally).

• 400 mg
• 500 mg
• 320 mg
• 800 mg

Correct Answer: 500 mg

Q10. Which single laboratory or clinical parameter is essential to compute a loading dose for a target total plasma concentration?

• Clearance (Cl)
• Half‑life (t1/2)
• Volume of distribution (Vd)
• Serum creatinine

Correct Answer: Volume of distribution (Vd)

Q11. How does a change in plasma protein binding (e.g., increased free fraction) usually affect the loading dose when the therapeutic target is total plasma concentration?

• Loading dose must be increased because free fraction increased
• Loading dose must be decreased because free fraction increased
• Loading dose remains the same because target is total concentration
• Protein binding changes make loading dose calculation impossible

Correct Answer: Loading dose remains the same because target is total concentration

Q12. For a multi‑compartment drug where rapid achievement of the plasma concentration is required, the loading dose should ideally be based on which volume?

• Volume of the peripheral compartment only
• Volume of distribution at steady state (Vdss)
• Volume of the central compartment (Vc)
• Renal clearance volume

Correct Answer: Volume of the central compartment (Vc)

Q13. Which statement is true regarding the relationship between volume of distribution and loading dose?

• Larger Vd results in a smaller loading dose for the same target concentration
• Loading dose is independent of Vd
• Larger Vd results in a larger loading dose for the same target concentration
• Vd only affects maintenance dose, not loading dose

Correct Answer: Larger Vd results in a larger loading dose for the same target concentration

Q14. A drug has Vd = 70 L, desired plasma concentration 15 mg/L, and oral bioavailability F = 0.5. What loading dose is required?

• 525 mg
• 1050 mg
• 2100 mg
• 700 mg

Correct Answer: 2100 mg

Q15. Which pharmacokinetic parameter primarily determines the maintenance infusion rate required to maintain a target steady‑state concentration?

• Volume of distribution (Vd)
• Clearance (Cl)
• Half‑life (t1/2)
• Salt factor (S)

Correct Answer: Clearance (Cl)

Q16. Calculate the loading dose (amount of salt to give) for a 60 kg patient when Vd = 0.2 L/kg, desired plasma concentration = 20 mg/L, bioavailability F = 0.8 and salt factor S = 0.5.

• 300 mg
• 600 mg
• 1200 mg
• 2400 mg

Correct Answer: 600 mg

Q17. If a bolus loading dose of 500 mg is administered IV and the apparent Vd is 50 L, what initial plasma concentration is expected (F = 1)?

• 0.1 mg/L
• 10 mg/L
• 25 mg/L
• 100 mg/L

Correct Answer: 10 mg/L

Q18. If the therapeutic target is a free (unbound) plasma concentration of 2 mg/L and the fraction unbound (fu) is 0.1, what total plasma concentration should be used in the loading dose calculation?

• 0.2 mg/L
• 2 mg/L
• 20 mg/L
• 200 mg/L

Correct Answer: 20 mg/L

Q19. Which statement best describes how to approach rapid attainment of target concentration when both loading dose and infusion are used?

• The loading dose magnitude is determined by clearance and the infusion rate by Vd
• The loading dose magnitude is determined by Vd and the infusion rate by clearance
• Both loading dose and infusion rate are determined only by Vd
• The infusion rate should always be zero if a loading dose is given

Correct Answer: The loading dose magnitude is determined by Vd and the infusion rate by clearance

Q20. In which clinical situation is a loading dose most appropriately given?

• For a short‑acting drug when delayed effect is acceptable
• When rapid attainment of therapeutic concentration is required and drug has a long half‑life
• Only when bioavailability is 100%
• Loading doses are only used for drugs administered orally

Correct Answer: When rapid attainment of therapeutic concentration is required and drug has a long half‑life

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