Step 1: Understanding the Question:
The question asks which tonicity adjustment method belongs to Class II.
Step 2: Key Formula or Approach:
Tonicity adjustment methods are grouped into two classes based on how the final preparation is built. Class I methods add water to the drug and any adjusting substance to reach the final isotonic volume. Class II methods instead add a calculated volume of an already isotonic vehicle to the drug, then finish with water if needed.
Step 3: Detailed Explanation:
The White Vincent method is a Class II approach. It uses the sodium chloride equivalent (E-value) of the drug to calculate how much isotonic vehicle to add:
\[ V = \frac{w \times E \times 111.1}{0.9} \]
Here \(w\) is the weight of the drug, \(E\) is its sodium chloride equivalent, and the constants come from the fact that 0.9 g of sodium chloride made up to 111.1 mL gives an isotonic solution. This calculated volume \(V\) of isotonic vehicle is added to the dissolved drug, and the preparation is then made up to its final volume with water. Because the isotonic vehicle itself supplies the tonicity, rather than water being added directly to the drug, this method is classified separately from the cryoscopic and sodium chloride equivalent methods, which belong to Class I.
Step 4: Final Answer:
The White Vincent method is the Class II method for tonicity adjustment.