Which statement about Class II methods is true?

• A. The diluting vehicle must be non-aqueous
• B. The E value is fixed at 0.3
• C. A hypertonic solution causes swelling; isotonic adjustments are used
• D. All statements are true

Answer: (C)

The main idea here is tonicity and how solutions interact with cells. A solution that is more concentrated than the inside of a cell (hypertonic) pulls water out of the cell, causing the cell to shrink. To keep such solutions compatible with body fluids, formulators make isotonic adjustments so the solution has the same osmotic pressure as blood and interstitial fluids. This is why isotonic adjustments are used: they prevent cellular shrinkage or swelling and help maintain stability and safety when a solution is introduced into the body. The notion that a hypertonic solution causes swelling is the opposite of what actually happens. Also, there isn’t a universal rule that the diluting vehicle must be non-aqueous, and there isn’t a single fixed E value that applies everywhere; tonicity considerations are the practical focus.