Pharmacy Pharmacokinetics 2 — Questions and Answers
Question 1: Which plasma protein is the primary binding protein for most acidic drugs?
- Alpha-1-acid glycoprotein (AAG)
- Albumin (Correct answer)
- Globulin
- Fibrinogen
Correct answer: Albumin
Albumin is the predominant plasma protein for binding acidic drugs (e.g., warfarin, NSAIDs), while alpha-1-acid glycoprotein primarily binds basic drugs.
Question 2: A patient with severe hypoalbuminemia is receiving a drug that is 95% protein-bound. What effect would you expect?
- Decreased free drug concentration and reduced effect
- Increased free drug concentration and potential toxicity (Correct answer)
- No change because total drug concentration is unchanged
- Increased renal clearance of the drug
Correct answer: Increased free drug concentration and potential toxicity
With less albumin available for binding, more drug remains unbound (free), increasing the pharmacologically active fraction and the risk of toxicity.
Question 3: Which of the following best describes zero-order pharmacokinetics?
- Drug concentration decreases by a fixed percentage per unit time
- Drug concentration decreases by a fixed amount per unit time and half-life increases with dose (Correct answer)
- Drug half-life remains constant regardless of dose
- Drug is rapidly eliminated and follows linear kinetics
Correct answer: Drug concentration decreases by a fixed amount per unit time and half-life increases with dose
Zero-order kinetics occur when elimination capacity is saturated; a constant amount (not percentage) of drug is eliminated per unit time, so half-life is not constant and increases with higher doses.
Question 4: Creatinine clearance (CrCl) is most commonly used clinically to estimate:
- Hepatic metabolic capacity
- Drug protein binding in plasma
- Renal function for drug dosing adjustments (Correct answer)
- Volume of distribution of renally cleared drugs
Correct answer: Renal function for drug dosing adjustments
CrCl is the standard marker for glomerular filtration rate (GFR) and is used to estimate renal function to guide dose adjustments for renally eliminated drugs.
Question 5: The Cockcroft-Gault equation is used in pharmacy practice to estimate:
- Hepatic clearance based on Child-Pugh score
- Creatinine clearance (CrCl) as a surrogate for GFR (Correct answer)
- Volume of distribution for obese patients
- Drug half-life in pediatric populations
Correct answer: Creatinine clearance (CrCl) as a surrogate for GFR
The Cockcroft-Gault equation estimates CrCl using serum creatinine, age, weight, and sex, and is the standard method for renal dose adjustment calculations.
Question 6: A drug follows first-order kinetics with a half-life of 6 hours. After 18 hours, approximately what percentage of the original dose remains?
- 50%
- 25%
- 12.5% (Correct answer)
- 6.25%
Correct answer: 12.5%
After 3 half-lives (18 hours = 3 × 6h), 50% → 25% → 12.5% remains; each half-life reduces the remaining drug by 50%.
Question 7: Steady-state plasma concentration during continuous dosing is typically reached after approximately:
- 1 half-life
- 3–5 half-lives (Correct answer)
- 10 half-lives
- The number depends only on dose size, not half-life
Correct answer: 3–5 half-lives
Steady state is reached when the rate of drug input equals the rate of elimination, which occurs after approximately 3–5 half-lives regardless of dose or dosing interval.
Pharmacy Pharmacokinetics 2
Which plasma protein is the primary binding protein for most acidic drugs?