How many milliliters of a 0.9% solution of sodium chloride should be used in compounding the prescription?

Question

Phenylephrine hydrochloride 1%

Chlorobutanol 0.5%

Sodium chloride qs

Purif ed water ad 15 mL

Make isotonic sol.

Sig. use as directed

Answer 1

Jenson, I am just now seeing your question and I notice it is from 24 days ago. You probably have your answer, but here's an explanation in case you do not:

There are steps to remember when determining isotonicity. Here are the steps when using the NaCl method

a. Determine the amount of each ingredient in the formula in grams

PE 0.01 x 15 mL = 0.15 g CH 0.005 x 15 mL = 0.075 g

b. Calculate the amount of NaCl represented by each ingredient by multiplying each amount by its E value; E for PE=0.32, CH = 0.24

PE 0.15 g x 0.32 = 0.048 g CH 0.075 g x 0.24 = 0.018g

c. Calculate the amount of NaCl that would be needed to make the quantity of 15 mL isotonic if nothing else was added. Remember, the concentration for an isotonic soln of NaCl is 0.9%

0.009 x 15 = 0.135 g NaCl needed

d. Subtract the amount of NaCl represented by each ingredient from the amount to make 15 mL isotonic

0.135 g - (0.048 g + 0.018 g) = 0.069 g NaCl to be added

e. Determine the volume of a 0.9% soln that would contain 0.069 g NaCl

0.9 g/100 mL = 0.069 g/x, x = 7.67 mL