Tuesday, 27 November 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.
     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.

 
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