Importance of isotonicity MCQs With Answer

Importance of isotonicity MCQs With Answer

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Importance of Isotonicity MCQs With Answer
Introduction for B. Pharm Students

Isotonicity is a core pharmaceutical concept affecting drug safety, stability and patient comfort. For B. Pharm students, understanding isotonicity, osmolarity, tonicity, NaCl equivalent (E‑value), freezing point depression and methods to adjust tonicity is essential for designing ophthalmic, parenteral and nasal formulations. Proper isotonicity prevents hemolysis, tissue irritation and therapeutic failure. This topic links physical chemistry (van’t Hoff law, osmotic pressure), formulation calculations (cryoscopic and E‑value methods) and clinical outcomes. Mastery helps you predict interactions of electrolytes, non‑electrolytes and metabolizable solutes like dextrose. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What does “isotonicity” refer to in pharmaceutical solutions?

  • A solution having same color as blood
  • A solution having the same osmotic pressure as body fluids
  • A solution that is sterile and pyrogen‑free
  • A solution with identical pH to plasma

Correct Answer: A solution having the same osmotic pressure as body fluids

Q2. Which formulation is most sensitive to isotonicity for patient comfort?

  • Topical creams
  • Ophthalmic eye drops
  • Tablets for oral use
  • Transdermal patches

Correct Answer: Ophthalmic eye drops

Q3. What is the clinical risk of administering a hypotonic IV solution?

  • Red blood cell hemolysis
  • red blood cell crenation
  • Increased blood viscosity
  • Enhanced plasma protein binding

Correct Answer: Red blood cell hemolysis

Q4. Which of the following is TRUE about 5% dextrose in water (D5W)?

  • It remains isotonic indefinitely in the circulation
  • It is initially isotonic but becomes effectively hypotonic after metabolism
  • It is a hypertonic solution that draws fluid into the vascular compartment
  • It cannot be used intravenously due to tonicity issues

Correct Answer: It is initially isotonic but becomes effectively hypotonic after metabolism

Q5. Which method directly measures freezing point depression to assess isotonicity?

  • Osmotic pressure calculation using van’t Hoff
  • NaCl equivalent (E‑value) method
  • Cryoscopic method
  • pH titration method

Correct Answer: Cryoscopic method

Q6. The NaCl equivalent (E‑value) of a drug is defined as:

  • The concentration of drug equivalent to 0.9% NaCl in volume
  • Grams of NaCl that produce the same osmotic effect as 1 g of drug
  • The molar mass ratio of drug to NaCl
  • The freezing point of the drug solution

Correct Answer: Grams of NaCl that produce the same osmotic effect as 1 g of drug

Q7. Which statement best distinguishes osmolarity from tonicity?

  • Osmolarity measures particles per kg solvent; tonicity is unrelated
  • Osmolarity counts all solute particles; tonicity considers only effective osmoles that affect cells
  • Tonicity measures only electrolytes; osmolarity measures only non‑electrolytes
  • They are identical terms and interchangeable

Correct Answer: Osmolarity counts all solute particles; tonicity considers only effective osmoles that affect cells

Q8. Plasma osmolality normally lies approximately within which range?

  • 100–120 mOsm/kg
  • 200–220 mOsm/kg
  • 285–295 mOsm/kg
  • 400–420 mOsm/kg

Correct Answer: 285–295 mOsm/kg

Q9. Why is osmotic activity of electrolytes higher than that of equivalent non‑electrolytes?

  • Electrolytes are heavier molecules
  • They dissociate into multiple particles increasing particle count
  • Electrolytes do not contribute to osmotic pressure
  • They bind water and reduce osmosis

Correct Answer: They dissociate into multiple particles increasing particle count

Q10. Which equation describes the relationship for ideal osmotic pressure?

  • π = iCRT (van’t Hoff equation)
  • ΔG = RT ln K
  • pH = pKa + log[A‑]/[HA]
  • PV = nRT for gases only

Correct Answer: π = iCRT (van’t Hoff equation)

Q11. A drug has a positive NaCl equivalent (E‑value). To make an isotonic solution, you should:

  • Always add more drug without adjusting other components
  • Adjust formulation by adding NaCl or dilution based on E‑value calculations
  • Ignore tonicity because drug effect dominates
  • Remove water to concentrate the solution

Correct Answer: Adjust formulation by adding NaCl or dilution based on E‑value calculations

Q12. Which of the following is a common tonicity adjustment agent?

  • Hydrochloric acid
  • Sodium chloride
  • Sodium lauryl sulfate
  • Polyvinyl alcohol

Correct Answer: Sodium chloride

Q13. The White‑Vincent method is used to:

  • Calculate pH adjustments for stability
  • Determine isotonic dosing based on NaCl equivalents
  • Measure sterility of parenteral products
  • Assess viscosity of ophthalmic solutions

Correct Answer: Determine isotonic dosing based on NaCl equivalents

Q14. If an ophthalmic solution is hypertonic relative to tears, patients will most likely experience:

  • Improved tear production and comfort
  • Ocular irritation and reflex tearing
  • Permanent vision enhancement
  • Complete drug inactivity

Correct Answer: Ocular irritation and reflex tearing

Q15. Which solute will NOT contribute to tonicity after being rapidly metabolized in tissues?

  • Glucose (dextrose)
  • Sucrose (non‑metabolizable in plasma)
  • Sodium chloride
  • Mannitol (impermeant osmotic agent)

Correct Answer: Glucose (dextrose)

Q16. What is the physiological significance of 0.9% w/v NaCl?

  • It is an antiseptic solution
  • It approximates isotonicity with human plasma
  • It is hypertonic and used to dehydrate tissues
  • It is used exclusively as a preservative

Correct Answer: It approximates isotonicity with human plasma

Q17. Which factor must be considered when using NaCl equivalent (E‑value) tables?

  • E‑values are universal for all solvents
  • E‑values may vary with ionic strength and temperature, so experimental conditions matter
  • E‑values only apply to sterile products
  • E‑values give pH directly

Correct Answer: E‑values may vary with ionic strength and temperature, so experimental conditions matter

Q18. Osmolality differs from osmolarity in that osmolality is expressed per:

  • Liter of solution
  • Kilogram of solvent (water)
  • Mole of solute only
  • Unit of pressure

Correct Answer: Kilogram of solvent (water)

Q19. Which statement is correct about impermeant solutes in relation to tonicity?

  • Impermeant solutes do not affect tonicity
  • Impermeant solutes determine tonicity because they cannot cross cell membranes
  • Only permeant solutes influence tonicity
  • Impermeant solutes are always electrolytes

Correct Answer: Impermeant solutes determine tonicity because they cannot cross cell membranes

Q20. Which laboratory method estimates isotonicity without extensive calculation?

  • Freezing point osmometry (cryoscopy)
  • Gas chromatography
  • Ultraviolet spectrophotometry
  • pH meter

Correct Answer: Freezing point osmometry (cryoscopy)

Q21. For an IV formulation, why is matching tonicity important besides avoiding hemolysis?

  • To ensure the solution tastes good
  • To prevent vascular irritation and pain at the infusion site
  • To increase the drug’s half‑life dramatically
  • To sterilize the solution automatically

Correct Answer: To prevent vascular irritation and pain at the infusion site

Q22. Which of the following modifies tonicity by producing more particles per molecule in solution?

  • Adding a non‑electrolyte like glycerol
  • Adding an electrolyte that dissociates, such as NaCl
  • Reducing temperature only
  • Using a colorant

Correct Answer: Adding an electrolyte that dissociates, such as NaCl

Q23. A drug increases freezing point depression more than predicted by its molar concentration. This likely indicates:

  • Non‑ideal behavior such as dissociation or association
  • The drug is inert and has no osmotic effect
  • The measurement instrument is irrelevant
  • The solution has become gaseous

Correct Answer: Non‑ideal behavior such as dissociation or association

Q24. Which choice correctly describes the role of van’t Hoff factor (i) in tonicity calculations?

  • It corrects for the number of particles each solute produces in solution
  • It determines the color of the solution
  • It is used only for pH adjustments
  • It replaces molar mass in all equations

Correct Answer: It corrects for the number of particles each solute produces in solution

Q25. If a preservative is highly hypertonic, how can formulation tonicity be corrected?

  • Add more preservative
  • Adjust with appropriate amount of water or NaCl equivalent to reach isotonicity
  • Make the product more viscous
  • Reduce sterilization time

Correct Answer: Adjust with appropriate amount of water or NaCl equivalent to reach isotonicity

Q26. Why are isotonicity calculations important during scale‑up of parenteral manufacturing?

  • Tonicity issues may change with concentration and can affect safety and stability at larger scale
  • Tonicity has no effect during scale‑up
  • Scale‑up only affects color and pH, not tonicity
  • Regulatory agencies do not require isotonicity control

Correct Answer: Tonicity issues may change with concentration and can affect safety and stability at larger scale

Q27. Which statement about the use of dextrose as a tonicity agent is correct?

  • Dextrose is always preferred because it is non‑metabolizable
  • Dextrose can be used but becomes less osmotically active after metabolism
  • Dextrose does not contribute to osmotic pressure at all
  • Dextrose permanently increases tonicity in tissues

Correct Answer: Dextrose can be used but becomes less osmotically active after metabolism

Q28. In calculating isotonicity by NaCl equivalent method, which data is essential?

  • Drug’s E‑value and amount to be added
  • Color of the drug
  • Boiling point only
  • Manufacturer’s address

Correct Answer: Drug’s E‑value and amount to be added

Q29. What happens to a red blood cell in a hypertonic solution?

  • It swells and bursts
  • It shrinks (crenation) due to water efflux
  • It becomes more permeable to large proteins
  • It turns into white blood cell

Correct Answer: It shrinks (crenation) due to water efflux

Q30. Which practice ensures ophthalmic formulations are comfortable and non‑irritant to patients?

  • Ignoring tonicity and focusing on color only
  • Adjusting pH and tonicity (isotonicity) and using appropriate preservatives
  • Making the solution extremely hypertonic to preserve it
  • Using high concentrations of alcohol for clarity

Correct Answer: Adjusting pH and tonicity (isotonicity) and using appropriate preservatives

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