B.Pharm. Bachelor of Pharmacy Biopharmaceutics & Pharmacokinetics 1 — Questions and Answers
Question 1: Bioavailability is defined as the fraction of an administered dose of drug that reaches the:
- Gastrointestinal tract unchanged
- Systemic circulation in active form (Correct answer)
- Liver before metabolism
- Target receptor site
Correct answer: Systemic circulation in active form
Bioavailability (F) measures the fraction of an administered dose that reaches the systemic circulation in unchanged, active form and is available to exert pharmacological effects.
Question 2: Which pharmacokinetic parameter describes the volume of plasma completely cleared of a drug per unit time?
- Volume of distribution
- Clearance (Correct answer)
- Half-life
- Bioavailability
Correct answer: Clearance
Clearance (Cl) is the pharmacokinetic parameter defined as the volume of plasma completely cleared of a drug per unit time, typically expressed in mL/min or L/hr.
Question 3: The first-pass effect refers to the metabolism of a drug that occurs:
- In the kidneys before excretion
- In the gut wall and liver before reaching systemic circulation (Correct answer)
- In the plasma after absorption
- At the site of drug administration
Correct answer: In the gut wall and liver before reaching systemic circulation
The first-pass effect (presystemic metabolism) occurs in the gut wall and liver, where orally administered drugs are extensively metabolized before reaching the systemic circulation, reducing bioavailability.
Question 4: Which route of administration completely bypasses the first-pass effect?
- Oral
- Rectal
- Intravenous (Correct answer)
- Sublingual
Correct answer: Intravenous
Intravenous (IV) administration delivers the drug directly into the systemic circulation, completely bypassing the liver and gut wall, thus avoiding the first-pass effect entirely.
Question 5: The biological half-life of a drug is the time required for the plasma drug concentration to:
- Reach its maximum value
- Decrease by 50% (Correct answer)
- Reach steady-state
- Fall to zero
Correct answer: Decrease by 50%
The half-life (t½) is the time required for the plasma drug concentration to decrease by exactly 50%, and it governs the dosing frequency and time to reach steady-state.
Question 6: The one-compartment open model assumes that the drug:
- Distributes unequally between tissues
- Behaves as if the entire body is a single homogeneous unit (Correct answer)
- Is eliminated only by renal excretion
- Has non-linear pharmacokinetics
Correct answer: Behaves as if the entire body is a single homogeneous unit
The one-compartment open model treats the body as a single homogeneous compartment where the drug distributes instantaneously and uniformly throughout, allowing rapid equilibration.
Question 7: In pharmacokinetic studies, Cmax refers to the:
- Minimum effective plasma drug concentration
- Maximum plasma drug concentration achieved after a single dose (Correct answer)
- Plasma concentration at steady state
- Concentration causing 50% of maximum effect
Correct answer: Maximum plasma drug concentration achieved after a single dose
Cmax is the peak or maximum plasma drug concentration observed after a single dose, and it is a key parameter for assessing the intensity of drug effect and potential toxicity.
