Lecture Math for the pharmacy technician: Concepts and calculations: Chapter 9 – Lynn M. Egler, Kathryn A. Booth

Chapter 9, Special preparations and calculations. This chapter presents information and calculations unique to compounds, alligations, preparation of a dilution from a concentrate, and special considerations for insulin calculations.

Math for the Pharmacy Technician:  Concepts and Calculations

Chapter 9: Special Preparations 

Egler • Booth

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Special Preparations and Calculations

Learning Objectives

 Determine the percentages of solutions,  dilutions, and solids.

 Prepare solutions from a concentrate.

 Prepare a compound.

 Measure insulin doses accurately.

When you have successfully completed Chapter 9, you will have  mastered skills to be able to:

mix two solids together  

method or the fractional proportion method.

 As you work through this chapter, both methods 

are used to solve for final volume/final strength. 

Initial volume

Initial

volume Final

2 g Lidocaine

10 g Zinc oxide

10% zinc oxide

Alligation Method  (con’t)

Concentration of  

HIGHER concentrated 

solution

Parts of the  HIGHER  concentrated  solution needed The concentration 

concentrated solution needed.

Alligation Method  (con’t)

5 Add a sufficient quantity of the less 

concentrated solution to bring the final  volume up to the desired volume.

Desired volume is 500 mL - you

would dilute the 90% by adding

water up to a final volume of 500

mL.

Preparing a Dilution from a 

Concentrate – Formula Method*

1 Identify the following information:

C n = the concentration needed

C a = the concentration available

V n = volume needed

2 Solve for:

V a = the volume available

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Preparing a Dilution from a Concentrate – Formula  Method (cont.)

3 Plug the values into the following formula:

Ca

Cn  

x  

Vn Va

4 Cancel units

5 Solve for the equation for V n

Review and Practice

Preparing a Dilution from a Concentrate –  Formula Method

How would you prepare 500 mL of 50% ethanol from 

90% ethanol?

needed to prepare 500 mL of a 50% solution

50% Ethanol

278 mL 90% ethanol

 For more accurate measurements, use a 50­

unit insulin syringe for insulin doses less than 

50 units when available, and a U­30 insulin  syringe for insulin doses less than 30 units of 

100 units/mL of insulin if these syringes are  available. 

Insulin Syringes  (con’t)

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Decide which syringe to use.

Ordered: Humulin R 55 units

Answer – 100-unit syringe and fill

it to between the 54 and 56 units

line

Review and Practice

career as a pharmacy technician.