## Tuesday, November 27, 2012

### Isotonicity

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  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.
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.