Question

A pharmacist is asked to compound 60 ml of an isotonic eye drop. drug x (a liquid with an e-value of 0.33) and sodium chloride will be used to prepare a final concentration of 1:500 (w/v). how many milligrams of sodium chloride must be added to make the eye drops isotonic?

Answer 1

The correct answer is 500mg.

First convert the ratio strength to a percentage(0.2%).

Drug X accounts for 0.0396 g of NaCl.

It would require 0.54 g of NaCl if that was all we were using.

Lastly, 0.54 g - 0.0396 = ~ 0.5 g NaCl ( or 500 mg, rounded as per the instructions ).