NAPLEX -Question Rapid Review: Board-Style
Q&A with Clinical Rationales
Q1. A patient receives a 500 mg IV bolus of a drug. The plasma concentration is 25 mg/L at 2 hours and 6.25 mg/L at 6 hours. What is the
elimination half-life?
- A) 1 hour
- B) 2 hours
- C) 4 hours
- D) 8 hours
**Answer:** B) 2 hours
**Rationale:** Concentration dropped from 25 to 6.25 over 4 hours (25→12.5→6.25). That is two half-lives in 4 hours, so half-life = 2 hours.
,Q2. Which equation correctly calculates the loading dose?
- A) (Css × Vd) / F
- B) (Css × CL) / τ
- C) (Css × Vd) / (F × S)
- D) (CL × Css) / (S × F)
**Answer:** A) (Css × Vd) / F
**Rationale:** Loading dose = Css × Vd / F (bioavailability). It fills the volume of distribution to reach steady state quickly.
**Q3.** A drug follows first-order kinetics. If the dose is doubled, the half-life will:
- A) Double
- B) Halve
- C) Remain the same
- D) Increase exponentially
**Answer:** C) Remain the same
**Rationale:** Half-life is independent of dose for first-order kinetics (t½ = 0.693/k).
,**Q4.** Which organ is primarily responsible for Phase I metabolism?
- A) Kidney
- B) Liver
- C) Lungs
- D) Skin
**Answer:** B) Liver
**Rationale:** The liver contains CYP450 enzymes, which perform oxidative Phase I reactions.
**Q5.** A patient has a creatinine clearance of 30 mL/min. Which antibiotic requires a dose adjustment?
- A) Azithromycin
- B) Ceftriaxone
- C) Levofloxacin
- D) Doxycycline
**Answer:** C) Levofloxacin
**Rationale:** Levofloxacin is renally eliminated; CrCl < 50 mL/min requires a dose reduction. Azithromycin and ceftriaxone are hepatically
eliminated, and doxycycline is safe in renal impairment.
, **Q6.** What does a high Vd (> total body water) indicate?
- A) The drug is confined to the plasma.
- B) The drug is highly protein bound.
- C) The drug is extensively distributed into tissues.
- D) The drug is renally cleared.
**Answer:** C) The drug is extensively distributed into tissues.
**Rationale:** High Vd means the drug leaves the plasma and enters tissues.
**Q7.** Bioavailability (F) compares the AUC of an oral dose to:
- A) Subcutaneous dose
- B) Intramuscular dose
- C) Intravenous dose
- D) Rectal dose
**Answer:** C) Intravenous dose
**Rationale:** IV is 100% bioavailable; F = AUC(oral)/AUC(IV).
**Q8.** Which drug is a strong CYP3A4 inhibitor?
Q&A with Clinical Rationales
Q1. A patient receives a 500 mg IV bolus of a drug. The plasma concentration is 25 mg/L at 2 hours and 6.25 mg/L at 6 hours. What is the
elimination half-life?
- A) 1 hour
- B) 2 hours
- C) 4 hours
- D) 8 hours
**Answer:** B) 2 hours
**Rationale:** Concentration dropped from 25 to 6.25 over 4 hours (25→12.5→6.25). That is two half-lives in 4 hours, so half-life = 2 hours.
,Q2. Which equation correctly calculates the loading dose?
- A) (Css × Vd) / F
- B) (Css × CL) / τ
- C) (Css × Vd) / (F × S)
- D) (CL × Css) / (S × F)
**Answer:** A) (Css × Vd) / F
**Rationale:** Loading dose = Css × Vd / F (bioavailability). It fills the volume of distribution to reach steady state quickly.
**Q3.** A drug follows first-order kinetics. If the dose is doubled, the half-life will:
- A) Double
- B) Halve
- C) Remain the same
- D) Increase exponentially
**Answer:** C) Remain the same
**Rationale:** Half-life is independent of dose for first-order kinetics (t½ = 0.693/k).
,**Q4.** Which organ is primarily responsible for Phase I metabolism?
- A) Kidney
- B) Liver
- C) Lungs
- D) Skin
**Answer:** B) Liver
**Rationale:** The liver contains CYP450 enzymes, which perform oxidative Phase I reactions.
**Q5.** A patient has a creatinine clearance of 30 mL/min. Which antibiotic requires a dose adjustment?
- A) Azithromycin
- B) Ceftriaxone
- C) Levofloxacin
- D) Doxycycline
**Answer:** C) Levofloxacin
**Rationale:** Levofloxacin is renally eliminated; CrCl < 50 mL/min requires a dose reduction. Azithromycin and ceftriaxone are hepatically
eliminated, and doxycycline is safe in renal impairment.
, **Q6.** What does a high Vd (> total body water) indicate?
- A) The drug is confined to the plasma.
- B) The drug is highly protein bound.
- C) The drug is extensively distributed into tissues.
- D) The drug is renally cleared.
**Answer:** C) The drug is extensively distributed into tissues.
**Rationale:** High Vd means the drug leaves the plasma and enters tissues.
**Q7.** Bioavailability (F) compares the AUC of an oral dose to:
- A) Subcutaneous dose
- B) Intramuscular dose
- C) Intravenous dose
- D) Rectal dose
**Answer:** C) Intravenous dose
**Rationale:** IV is 100% bioavailable; F = AUC(oral)/AUC(IV).
**Q8.** Which drug is a strong CYP3A4 inhibitor?
