MTM Renal Dosing & Adjustments 2 — Questions and Answers
Question 1: A patient with a CrCl of 25 mL/min is prescribed vancomycin. Which pharmacokinetic parameter is most affected by renal impairment for this drug?
- Volume of distribution
- Protein binding
- Elimination half-life (Correct answer)
- Oral bioavailability
Correct answer: Elimination half-life
Vancomycin is renally eliminated, so its half-life is prolonged significantly as CrCl declines.
Question 2: Which formula is most commonly used to estimate creatinine clearance in clinical practice for renal dosing adjustments?
- Modification of Diet in Renal Disease (MDRD)
- CKD-EPI equation
- Cockcroft-Gault equation (Correct answer)
- Schwartz equation
Correct answer: Cockcroft-Gault equation
The Cockcroft-Gault equation is the standard for estimating CrCl used in drug dosing adjustments in most FDA labeling.
Question 3: A 72-year-old woman weighing 50 kg with a serum creatinine of 1.0 mg/dL is prescribed a renally-cleared drug. Why might dosing based on her normal creatinine be misleading?
- Elderly patients absorb drugs faster
- Low muscle mass can cause falsely normal creatinine despite reduced GFR (Correct answer)
- Her liver metabolism is impaired
- Women have higher creatinine production than men
Correct answer: Low muscle mass can cause falsely normal creatinine despite reduced GFR
Elderly, low-muscle-mass patients may have reduced GFR despite normal serum creatinine because less creatinine is produced.
Question 4: Which antibiotic requires the MOST significant dose reduction in a patient with CrCl of 10 mL/min?
- Azithromycin
- Doxycycline
- Ciprofloxacin (Correct answer)
- Clindamycin
Correct answer: Ciprofloxacin
Ciprofloxacin is substantially renally eliminated and requires significant dose reduction when CrCl falls below 30 mL/min.
Question 5: When calculating CrCl using the Cockcroft-Gault equation for an obese patient (BMI 42), which weight should generally be used?
- Total body weight
- Ideal body weight
- Adjusted body weight (Correct answer)
- Lean body weight
Correct answer: Adjusted body weight
Adjusted body weight (IBW + 0.4 × [TBW − IBW]) is recommended for obese patients to avoid overestimating CrCl.
Question 6: A dialysis patient requires antibiotic therapy. Which agent can be used WITHOUT supplemental dosing after hemodialysis?
- Cefazolin
- Vancomycin (Correct answer)
- Gentamicin
- Levofloxacin
Correct answer: Vancomycin
Vancomycin is poorly dialyzed and generally does not require supplemental dosing after standard hemodialysis sessions.
Question 7: Which drug is CONTRAINDICATED in patients with CrCl < 30 mL/min due to accumulation of a toxic metabolite?
- Metformin
- Meperidine (Correct answer)
- Gabapentin
- Lisinopril
Correct answer: Meperidine
Meperidine's metabolite normeperidine accumulates in renal impairment and can cause neurotoxicity and seizures.
MTM Renal Dosing & Adjustments 2
A patient with a CrCl of 25 mL/min is prescribed vancomycin.
Which pharmacokinetic parameter is most affected by renal impairment for this drug?