DHA Pharmacist Pharmaceutical Sciences 1 — Questions and Answers
Question 1: Which pharmacokinetic parameter describes the fraction of an administered drug dose that reaches systemic circulation unchanged?
- Bioavailability (F) (Correct answer)
- Volume of distribution (Vd)
- Clearance (CL)
- Half-life (t½)
Correct answer: Bioavailability (F)
Bioavailability (F) quantifies the proportion of an administered drug that reaches the systemic circulation, reflecting absorption and first-pass metabolism effects.
Question 2: What is the primary site of drug metabolism in the body?
- Liver (Correct answer)
- Kidney
- Lung
- Small intestine only
Correct answer: Liver
The liver is the primary organ for drug metabolism, containing abundant cytochrome P450 enzymes that transform drugs into more water-soluble metabolites for excretion.
Question 3: Which drug formulation property determines whether a tablet should NOT be crushed?
- Extended-release (ER/XR) coating or enteric coating (Correct answer)
- Standard immediate-release coating
- Plain sugar coating
- Coloured coating only
Correct answer: Extended-release (ER/XR) coating or enteric coating
Extended-release and enteric-coated tablets have specialised coatings that control drug release rate or protect the stomach; crushing destroys this mechanism and can cause toxicity or reduced efficacy.
Question 4: What is the Henderson-Hasselbalch equation used for in pharmacy?
- Calculating the degree of ionisation of a drug at a given pH (Correct answer)
- Calculating dose adjustments in renal failure
- Determining drug storage temperature
- Estimating bioavailability
Correct answer: Calculating the degree of ionisation of a drug at a given pH
The Henderson-Hasselbalch equation relates pH, pKa, and the ratio of ionised to un-ionised drug, predicting drug absorption and distribution across biological membranes.
Question 5: Which process describes the elimination of a drug from the body at a constant fraction per unit time, regardless of plasma concentration?
- First-order elimination kinetics (Correct answer)
- Zero-order elimination kinetics
- Michaelis-Menten kinetics
- Saturation kinetics
Correct answer: First-order elimination kinetics
First-order kinetics means a constant percentage of the drug is eliminated per unit time, so the rate of elimination is proportional to the plasma concentration.
Question 6: Which factor most significantly affects the volume of distribution (Vd) of a highly lipophilic drug?
- Extensive distribution into adipose and peripheral tissues resulting in a large Vd (Correct answer)
- High plasma protein binding causing a small Vd
- Rapid renal excretion limiting distribution
- Water solubility causing restriction to plasma only
Correct answer: Extensive distribution into adipose and peripheral tissues resulting in a large Vd
Highly lipophilic drugs partition extensively into fatty tissues and peripheral compartments, resulting in a large volume of distribution far exceeding actual body water volume.
DHA Pharmacist Pharmaceutical Sciences 1
Which pharmacokinetic parameter describes the fraction of an administered drug dose that reaches systemic circulation unchanged?