Question

CLASS-II method for tonicity adjustment is:

• A. Cryoscopic
• B. NaCl Equivalent
• C. White Vincent
• D. Mole fraction

Hint:

White Vincent method is especially useful in hospital and extemporaneous formulations to make isotonic solutions accurately without prior measurement of final volume.

Answer 1

The Correct Option is C

Tonicity adjustment is a critical step in pharmaceutical formulations, especially for parenteral, ophthalmic, and nasal preparations. The White Vincent method is categorized under Class II methods of tonicity adjustment. Class II methods are used when the volume of the solution needs to be adjusted after the addition of the drug. The White Vincent method calculates the volume of isotonic solution to be prepared by using the sodium chloride equivalent (E-value) of the drug. White Vincent Formula: \[ V = \frac{w \times E \times 111.1}{0.9} \] Where: - \( V \) = volume of isotonic solution (in mL)
- \( w \) = weight of drug (in grams)
- \( E \) = NaCl equivalent value of the drug
- 0.9 = concentration of normal saline (in %)
- 111.1 = volume (in mL) that 0.9 g NaCl will make isotonic
Explanation of options: - (a) Cryoscopic: Class I method based on freezing point depression.
- (b) NaCl Equivalent: Concept used in several methods but not a method itself.
- (c) White Vincent: Correct. It is a Class II method.
- (d) Mole fraction: Not commonly used for tonicity adjustments in practical pharmaceutics.

Answer 2

This question asks which listed method for adjusting tonicity is classified as a Class II method. Checking how each method actually works, and specifically when the final volume of the preparation is decided, sorts them into their correct class.

1. Cryoscopic: The cryoscopic method calculates how much sodium chloride or another adjusting substance is needed based on the freezing point depression of the drug solution. It works by adding water to the drug to reach a set volume, which places it among the Class I methods.
2. NaCl Equivalent: The sodium chloride equivalent is a value used within several tonicity calculations, describing how much sodium chloride would produce the same osmotic effect as a given weight of drug. It is a quantity used inside a method, not a method or a class on its own.
3. White Vincent: This method starts by dissolving the drug and adding an isotonic vehicle to reach a calculated intermediate volume, then makes up the rest of the final volume with plain water. Because the amount of isotonic vehicle added, not just water, determines the outcome, this approach falls under Class II methods.
4. Mole fraction: The mole fraction method estimates tonicity from the proportion of solute molecules to solvent molecules in the preparation. It is a calculation approach based on colligative properties, not one of the two standard tonicity adjustment classes used in this classification.

Class I methods add water to the drug to reach isotonicity, while Class II methods add a calculated volume of isotonic vehicle to the drug, and White Vincent follows this second approach.

So the correct answer is White Vincent.