Question

How many milliliters of a 1% w/v epinephrine injection must be used to prepare 20 mL of an injection containing 1:200,000 w/v epinephrine?

Answer 1

Ans. # Step 1: A 1% (w/v) means there is 1.0 g of solute per 100.0 mL of the solution.

So, stock [Epn] = 1.0 g Epn / 100 mL solution

# While preparing stock solution, 1 g of pure solid epinephrine would be dissolved to yield 100 mL of solution.

1^st Dilution factor in stock [Epn] = Mass of solute / Total vol. made up to

                                                = 1 g / 100 mL = 1 / 100

# Step 2: Given- we have to prepare (1 : 200000) w/v epinephrine – 20 mL quantity.

That is, the total dilution factor (from solid epinephrine to final diluted solution) is 1/200000.

            We have, 1^st dilution factor = 1/ 100

            Let the 2^nd dilution factor be X

Now,

            Total dilution factor = 1^st DF x 2^nd DF = 1 / 200000

            Or, (1/ 100) x X = 1 / 200000

            Or, X = (1 / 200000) / (1 / 100) = 1 / 2000

Hence, second dilution factor = 1 / 2000

# Step 3: Preparing the final solution

From #Step 2, second dilution factor = 1 / 2000

That is, when is dilute the stock [Epn] 2000 times, the resultant solution would be 1/200000 w/v.

# Given, required volume of dilute soln. = 20 mL

Now,

            Required volume of Stock [Epn] = 2^nd DF x required volume of dilute soln.

                                                            = (1/2000) x 20 mL

                                                            = 0.01 mL = 10.0 uL

# Preparation: Take 10.0 uL of the stock epinephrine solution in a clean 25-mL test tube (or other suitable glassware). To this, add 19.99 mL (= 19990 uL) of suitable diluent (distilled water or normal saline or as instructed). Mix well. The resultant solution is 1/200000 w/v epinephrine.