How to compute for the weight of Sodium Chloride or Substance to make a solution isotonic.
Step 1: NaCl Equivalent of the Active x Wt of the Active = Wt. of NaCl represented by Active
(See the Table of NaCl Equivalents)
Step 2: Volume of Solution x 0.9%NaCl = Wt of NaCl in volume solution of an isotonic NaCl solution
Step 3: Answer from Step 2 - Answer from Step 1 = Wt of NaCl needed to be used
*Step 4: Answer from Step 3 / NaCl equivalent of Substance needed = Wt of substance needed to
to make the solution isotonic cause the solution isotonic
*Step 4 will be needed when NaCl does not cause the solution isotonic.
Example:
How many grams of sodium chloride should be used in compounding the prescription?
Rx
Zinc Sulfate 0.08g
Boric Acid q.s.
Purified Water ad 10ml
Make isotonic solution
Sig. Drop in eyes.
Solutions:
Step 1: 0.16 x 0.08g = 0.0128g NaCl represented by Zinc Sulfate
Step 2: 10 x 0.9% = 0.09g NaCl in 10ml of an isotonic NaCl solution
Step 3: 0.09g - 0.0128g = 0.0772g NaCl to be used, but in this case boric acid is to be used so proceed
on Step 4.
Step 4: 0.0772g / 0.52 = 0.1485g of boric acid needed to make the solution isotonic.
