GPhC Pharmaceutical Sciences & Calculations 3 — Questions and Answers
Question 1: What is the osmolarity of normal saline (0.9% NaCl) approximately?
- 308 mOsm/L (Correct answer)
- 154 mOsm/L
- 500 mOsm/L
- 100 mOsm/L
Correct answer: 308 mOsm/L
0.9% NaCl dissociates into Na+ and Cl−, each at 154 mmol/L, giving approximately 308 mOsm/L, which is isotonic with blood.
Question 2: Which type of interaction occurs when two drugs compete for the same plasma protein binding site?
- Pharmacokinetic displacement interaction (Correct answer)
- Pharmacodynamic interaction
- Synergistic interaction
- Additive interaction
Correct answer: Pharmacokinetic displacement interaction
Protein binding displacement is a pharmacokinetic interaction where one drug displaces another from albumin or other proteins, increasing free drug concentration.
Question 3: A suppository base that melts at body temperature is described as:
- Theobroma oil base (Correct answer)
- Hydrophilic base
- Macrogol base
- Glycerin base
Correct answer: Theobroma oil base
Theobroma oil (cocoa butter) melts at approximately 34–35°C, close to body temperature, making it suitable for rectal suppositories.
Question 4: What does 'bioavailability' refer to?
- The fraction of administered drug that reaches systemic circulation (Correct answer)
- The speed at which a drug is metabolised
- The volume in which a drug distributes
- The rate of renal excretion
Correct answer: The fraction of administered drug that reaches systemic circulation
Bioavailability (F) is the proportion of an administered dose that reaches the systemic circulation unchanged. IV administration gives 100% bioavailability.
Question 5: Which polymorphic form of a drug is generally more soluble?
- Amorphous form (Correct answer)
- Crystalline form
- Hydrate form
- Anhydrous form
Correct answer: Amorphous form
Amorphous solids lack a regular crystal lattice, making them more soluble and often more bioavailable than crystalline forms of the same drug.
Question 6: In a first-order elimination process, when plasma concentration doubles, the elimination rate:
- Doubles (Correct answer)
- Stays the same
- Halves
- Quadruples
Correct answer: Doubles
In first-order kinetics, the rate of elimination is proportional to the drug concentration. If concentration doubles, so does the elimination rate.
GPhC Pharmaceutical Sciences & Calculations 3
What is the osmolarity of normal saline (0.9% NaCl) approximately?