B.Pharm. Bachelor of Pharmacy Biopharmaceutics & Pharmacokinetics 2 — Questions and Answers
Question 1: The therapeutic index (TI) of a drug is defined as the ratio of:
- ED50 to LD50
- LD50 to ED50 (Correct answer)
- Cmax to Cmin
- AUC to half-life
Correct answer: LD50 to ED50
The therapeutic index is calculated as LD50/ED50; a higher TI indicates a greater margin of safety between the lethal dose and the effective dose of a drug.
Question 2: Zero-order kinetics means that the rate of drug elimination is:
- Proportional to plasma drug concentration
- Constant and independent of plasma drug concentration (Correct answer)
- Exponential over time
- Dependent on protein binding
Correct answer: Constant and independent of plasma drug concentration
In zero-order kinetics, a constant amount of drug is eliminated per unit time regardless of plasma concentration, typically occurring when elimination mechanisms are saturated (e.g., ethanol, phenytoin at high doses).
Question 3: The absorption rate constant (Ka) is used to describe:
- The rate of drug distribution into tissues
- The speed at which a drug is absorbed from the site of administration into systemic circulation (Correct answer)
- The rate of renal drug excretion
- The rate of hepatic drug metabolism
Correct answer: The speed at which a drug is absorbed from the site of administration into systemic circulation
Ka (absorption rate constant) quantifies how quickly a drug moves from its site of administration into the systemic circulation, influencing Tmax and Cmax values.
Question 4: The Area Under the Curve (AUC) in pharmacokinetics represents:
- Peak plasma drug concentration
- Total drug exposure over time (Correct answer)
- Volume of drug distribution
- Rate of drug clearance
Correct answer: Total drug exposure over time
AUC (Area Under the plasma concentration-time Curve) represents the total drug exposure over time and is directly proportional to the total amount of drug that reaches systemic circulation.
Question 5: Highly plasma protein-bound drugs have a characteristically:
- Large volume of distribution and short half-life
- Small volume of distribution and prolonged half-life (Correct answer)
- Rapid renal clearance and high free fraction
- Low bioavailability and fast onset
Correct answer: Small volume of distribution and prolonged half-life
Drugs extensively bound to plasma proteins remain in the vascular compartment (small Vd), are protected from metabolism/excretion, and have a prolonged half-life due to reduced free drug available for elimination.
Question 6: Enterohepatic circulation involves the recycling of drugs or metabolites through the:
- Kidney and bladder loop
- Liver, bile, intestine, and portal vein (Correct answer)
- Lung and pulmonary circulation
- Lymph and thoracic duct
Correct answer: Liver, bile, intestine, and portal vein
Enterohepatic circulation occurs when a drug or its conjugated metabolite is excreted in bile, deconjugated by gut bacteria in the intestine, reabsorbed, and returned to the liver via the portal vein, prolonging drug action.
Question 7: A drug with a volume of distribution (Vd) of 200 L in a 70 kg person suggests the drug is:
- Confined mainly to the plasma
- Extensively distributed into peripheral tissues (Correct answer)
- Bound primarily to albumin in blood
- Eliminated rapidly by the kidneys
Correct answer: Extensively distributed into peripheral tissues
A large Vd (e.g., 200 L far exceeds plasma volume of ~3 L and total body water of ~42 L) indicates extensive distribution into peripheral tissues and/or intracellular compartments.
B.Pharm. Bachelor of Pharmacy Biopharmaceutics & Pharmacokinetics 2
The therapeutic index (TI) of a drug is defined as the ratio of: