Pharm.D. Doctor of Pharmacy Pharmacokinetics and Pharmacodynamics 2 — Questions and Answers
Question 1: Which equation is used to calculate drug clearance from area under the curve (AUC)?
- CL = Dose / AUC (Correct answer)
- CL = Vd × ke
- CL = AUC × t½
- CL = F × Dose
Correct answer: CL = Dose / AUC
Clearance is calculated as CL = Dose / AUC (after IV dosing), relating the administered dose to total drug exposure.
Question 2: Which type of drug interaction involves competition for the same plasma protein binding site?
- Pharmacodynamic antagonism
- Pharmacokinetic displacement (Correct answer)
- Receptor downregulation
- Enzyme induction
Correct answer: Pharmacokinetic displacement
Pharmacokinetic displacement occurs when two drugs compete for the same plasma protein binding sites, potentially increasing free drug concentration of one.
Question 3: The therapeutic index (TI) is calculated as:
- TD50 / ED50 (Correct answer)
- ED50 / TD50
- LD50 / ED50
- ED50 / LD50
Correct answer: TD50 / ED50
The therapeutic index is TD50 / ED50, representing the ratio of the toxic dose to the effective dose — a higher TI indicates a safer drug.
Question 4: Renal clearance of a drug is primarily affected by which three processes?
- Absorption, distribution, metabolism
- Filtration, secretion, reabsorption (Correct answer)
- Protein binding, ionization, lipophilicity
- Conjugation, hydroxylation, glucuronidation
Correct answer: Filtration, secretion, reabsorption
Renal drug clearance depends on glomerular filtration, active tubular secretion, and tubular reabsorption of the drug.
Question 5: Which cytochrome P450 enzyme is most responsible for the metabolism of the majority of clinically used drugs?
- CYP1A2
- CYP2D6
- CYP3A4 (Correct answer)
- CYP2C9
Correct answer: CYP3A4
CYP3A4 is the most abundant hepatic CYP enzyme and is responsible for metabolizing approximately 50% of all clinically used drugs.
Question 6: In a two-compartment pharmacokinetic model, the 'alpha' phase represents:
- Elimination from the body
- Distribution of drug into peripheral tissues (Correct answer)
- Absorption from the GI tract
- Renal secretion
Correct answer: Distribution of drug into peripheral tissues
In a two-compartment model, the alpha (distribution) phase reflects rapid decline in plasma drug concentration due to drug distribution into peripheral tissues.
Pharm.D. Doctor of Pharmacy Pharmacokinetics and Pharmacodynamics 2
Which equation is used to calculate drug clearance from area under the curve (AUC)?