NTA Level 4 • Semester 1 • PST04105

Calculations of Dilution and Concentration of Solids and Semisolids

Pharmaceutical Calculations • Source Session/Topic 18

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Session 18: Calculations of Dilution and Concentration of Solids and

Semisolids

Total Session Time: 60 minutes

Prerequisites

None

Learning Tasks

By the end of this session students are expected to be able to:

• Define dilution and concentration of Solids and Semisolids

• Calculating dilution and concentration of Solids and Semisolids

Resources Needed:

• Flip charts, marker pens, and masking tape

• Black/white board and chalk/whiteboard markers

SESSION OVERVIEW

SESSION CONTENTS

STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)

READ or ASK students to read the learning tasks and clarify

ASK students if they have any questions before continuing.

STEP 2: Definition of Dilution and Concentration of Solids and Semisolids

(20 Minutes)

|Activity: Brainstorming (5 minutes) |

| |

|Ask students to brainstorm on the following question: |

| |

|What is dilution and concentration of solids and Semisolids? |

| |

|ALLOW few students to respond |

| |

|WRITE their responses on the flip chart/ board |

| |

|CLARIFY and SUMMARISE by using the content below |

• The dilution of solids in pharmacy occurs when there is need to

achieve a lower concentration of an active component in a more

concentrated preparation (e.g., a powdered vegetable drug)

• There is also a type of diluted pharmaceutical preparation, termed a

trituration that represents a useful means of preparing and

administering very potent therapeutic substances

• Reducing or enhancing the strengths of creams and ointments is a usual

part of a compounding

Pharmaceutical personnel’s practice to meet the special needs of patients

• The dilution of semisolids is a usual part of a compounding

pharmaceutical personnel’s practice in reducing the strengths of

creams and ointments to meet the special needs of patients

STEP 3: Dilution and Concentration of Solids and Semisolids (25 Minutes)

|Activity: Small Group Discussion ( 15 minutes) |

| |

|DIVIDE students into small manageable groups |

| |

|ASK students to discuss on the following question |

|If 30 g of a 1% hydrocortisone ointment were diluted with 12 g of |

|Vaseline, what would be the concentration of hydrocortisone in the |

|mixture? |

| |

|How many grams of zinc oxide should be added to 3200 g of 5% zinc oxide|

|ointment to prepare an ointment containing 20% of zinc oxide? |

| |

|ALLOW students to discuss for 15 minutes |

| |

|ALLOW few groups to present and the rest to add points not mentioned |

| |

|CLARIFY and SUMMARIZE by using the contents below |

• The following are the solutions of the above exercises:

30 g x 1% = 0.3 g hydrocortisone

30 g x 12 g = 42 g, weight of mixture

0.3 g x 100 = 0.71% (w/w), answer.

42 g

Or,

30 (g) x 1 (%) = 42 (g) x x(%)

x = 0.71% (w/w), answer.

(2) 3200 g x 0.05 = 160 g of zinc oxide in 3200 g of 5% ointment

3200 g x 160 g = 3040 g of base (diluent) in 3200 g of 5% ointment

In the 20% ointment, the diluent will represent 80% of the total weight

80 (%) = 3040 (g)

20 (%) x (g)

x = 760 g of zinc oxide in the 20% ointment

Because the 5% ointment already contains 160 g of zinc oxide,

760 g – 160 g = 600 g, answer.

STEP 4: Key Points (5 minutes)

• The dilution of solid dosage forms such as powders or semisolids dosage

forms such as ointments and creams may be performed to alter the dose or

strength of the product

• The concentration of solid and semisolids dosage forms also known as

fortification, by addition of calculated quantity of additional

therapeutic agent, remains a viable practice in pharmaceutical

compounding

STEP 7: Evaluation (15 minutes)

• What is dilution of solids and semisolids?

• What is concentration if solids and semisolids?

• How many grams of 20% benzocaine ointment and how many grams of ointment

base (diluent) should be used in preparing 5 lb. of 2.5% benzocaine

ointment?

References

Ansel, H. C & Stocklosa, M. J. (2001). Pharmaceutical Calculations (11th

ed.). Philadelphia, United States: LIPPINCOTT WILLIAMS & WILKINS

Ansel, H. C (2010) Pharmaceutical Calculations (13rd ed.). Philadelphia,

United States: LIPPINCOTT WILLIAMS & WILKINS

Senya, S. S, Mwasha, C.Y, Muyinga, A. M, Amiri,R. I. and Mauga E.A.S.K.

(2011) Tanzania Pharmaceutical Handbook (2nd ed.). Dar eS Salaam,

Tanzania: School of Pharmaceutical Sciences.

Zatz, J.L and Teixeira, M.G. (2005). Pharmaceutical Calculation (4th ed.).

New Jersey: John Wiley & Sons

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