NTA Level 4 • Semester 1 • PST04105

Calculations of Quantities of Each Ingredient Required for Compounding

Pharmaceutical Calculations • Source Session/Topic 17

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Session 17: Calculations of Quantities of Each Ingredient Required for

Compounding

Total Session Time: 120 minutes + 1 hours Assignment

Prerequisites

• None

Learning Tasks

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

• Calculate the amount of drug required for compounding from a given

prescription

• Calculate the ratio (factor) of quantity needed for compounding

• Enlarge or reduce formula by using the factor

• Determine dilutions of reduced and enlarged formula

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: Calculating Amount of Drug Required for Compounding From a Given

Prescription (20 minutes)

When the amount of prescribed or ordered medicines deviates from the

official quantities of a formula in a reference book the amount of each

ingredient for compounding can be obtained or calculated

Example:

Dispense: Paracetamol syrup 250 mg tds 3/7,

Available Paracetamol syrup 125 mg Paracetamol per 5 mL

Solution;

250 mg (Paracetamol) × 3 × 3 = 2250 mg of Paracetamol.

5 mL of Paracetamol syrup contains 125 mg of Paracetamol

X mL of Paracetamol syrup will contains 2250 mg of Paracetamol.

(5 mL× 2250) / 125 = 90 mL of Paracetamol syrup to be dispensed, Answer

STEP 3: Calculating Ratio of Quantity Needed for Compounding (30 minutes)

In order to reduce or enlarge the formula the following ratio / factor are

the mostly used;

Factor = Total amount required / total amount of the official formula

Example of reducing formula:

Codeine phosphate syrup PCx:

Codeine phosphate———————————-5 gm

Purified water freshly boiled and cooled———15 mL

Chloroform spirit————————————25 mL

Syrup———————————————to 1000 mL

Sig; 5mL q.i.d 4/7

Solution:

Prescribed amount is: 5 × 4 × 4 = 80 mL

Factor = 80 mL/ 1000 mL

= 0.08

|Activity: Small Group Discussion ( 20 minutes) |

| |

|DIVIDE students into small manageable groups |

| |

|ASK students to discuss on the following question: |

| |

|Ammonium chloride mixture PCx |

|Ammonium chloride ——————————–10 gm |

|Aromatic ammonia solution————————5 mL |

|Liquorice liquid extract—————————–10 mL |

|Water for preparations————————–to 100mL |

|Sig; ammonium chloride mixture 10 mL tds 5/7 |

| |

|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 answers of the above exercise:

The amount of drug to be dispensed will be calculated as;

10 mL × 3 × 5 = 150 mL to be dispensed

Factor = Total amount required / total amount of the official formula

= 150 mL/ 100 mL

= 1.5, answer

STEP 4: Enlarging or Reducing of Formula by Using the Factor (20 minutes)

• Pharmaceutical personnel may have to reduce or enlarge formulas for

pharmaceutical preparations in the course of their practice

• Official formulas and most other formulas for manufacturing are based on

the preparation of 1000 mL or 1000 gm of product

The pharmaceutical personnel may be called on to make a smaller or greater

quantity and thus must reduce or enlarge the formula while maintain the

correct proportion of each ingredient

Examples:

• Reducing of the formula

Codeine phosphate syrup PCx

Official amount

|Codeine phosphate |5 gm |

|Purified water freshly boiled and cooled |15 mL |

|Chloroform spirit |25 mL |

|Syrup |to 1000 mL |

Sig; 5mL q.i.d 4/7

Solution;

Prescribed amount is: 5 × 4 × 4 = 80 mL

Factor = 80 mL/ 1000 mL

= 0.08

Hence the formula will be as follows

Codeine phosphate syrupPCx

|Codeine phosphate |5 gm |0.08 |0.4 gm |

|Purified water freshly boiled|15 mL |0.08 |1.2 mL |

|Chloroform spirit |25 mL |0.08 |2.0 mL |

|Syrup |to 1000 mL |0.08 |to 80 mL |

• Enlarging of formula

Ammonium chloride mixture PCx

| |Official amount |

|Ammonium chloride |10 gm |

|Aromatic ammonia solution |5 mL |

|Liquorice liquid extract |10 mL |

|Water for preparations |to 100mL |

Sig; ammonium chloride mixture 10 mL tds 5/7

The following are the answers of the above exercise

The amount of drug to be dispensed will be calculated as;

10 mL × 3 × 5 = 150 mL to be dispensed

Factor = Total amount required / total amount of the official formula

= 150 mL/ 100 mL

Factor = 1.5

Hence the formula will become;

Ammonium chloride mixture PCx

|Ammonium chloride |10 gm |1.5 |15 gm |

|Aromatic ammonia |5 mL |1.5 |7.5 mL |

|Liquorice liquid extract|10 mL |1.5 |15 mL |

|Water for preparations |to 100mL |1.5 |to 150 mL |

STEP 5: Determination of Dilution of Reduced and Enlarged Formulas (30

minutes)

• For many liquid oral preparations ( e, g mixtures, elixirs) B.P. and PCx.

State that when a dose ordered or prescribed is less than or not a

multiple of 5mL, the preparation should be diluted with the vehicle used

in the preparation or with diluents specified in the individual monograph

so that the dose to be measured by the patient is a 5 mL-spoonful

(usually taken as a teaspoonful) or multiple thereof

Example:

Codeine phosphate syrupPCx

Codeine phosphate———————————-5 gm

Purified water freshly boiled and cooled———15 mL

Chloroform spirit————————————25 mL

Syrup———————————————to 1000 mL

Sig; 2.5mL q.i.d 4/7

Solution

Prescribed amount is: 2.5 × 4 × 4 = 40 mL

Factor = 40 mL/ 1000 mL

= 0.04

As 2.5 mL is less than 5mL each single dose should be diluted with 2.5 mL

of diluents (in this case syrup), so that the patient can measure the dose

in terms of 5 mL teaspoonful

2.5mL × 4 × 4 = 40 mL Amount of undiluted preparation

2.5mL × 4 × 4 = 40 mL Amount of diluents (syrup)

5.0mL × 4 × 4 = 80 mL Amount of diluted preparation

Codeine phosphate syrupPCx

|Codeine phosphate |5 gm |0.04 |0.2 gm |0.2 gm |

|Purified water freshly |15 mL |0.04 |0.6 mL |0.6 mL |

|Chloroform spirit |25 mL |0.04 |1.0 mL |1.0 mL |

|Syrup |to 1000 mL |0.04 |to 40 mL |80.0 mL |

STEP 6: Key Points (5 minutes)

• When the amount of prescribed or ordered medicines deviates from the

official quantities of a formula in a reference book the amount of each

ingredient for compounding can be obtained or calculated.

• Factor = Total amount required / total amount of the official formula

STEP 7: Evaluation (5 minutes)

• What do you understand by the term “reducing and enlarging of formula?”

• Write the formula for calculating factor

• What do you understand by dilution in a reduced or enlarged formula?

STEP 8: Take Home Assignment (5 minutes)

|Activity: Take home Assignment (5 minutes) |

| |

|ASK each individual student to do the following assignment |

| |

|From the following formula calculate the amount of medicine to be |

|dispensed: |

|Asthma mixture TPH |

| |

|Official amount |

| |

|Ammonium bicarbonate |

|2.0 gm |

| |

|Potassium iodide |

|3.0 gm |

| |

|Belladonna tincture |

|3.0 gm |

| |

|Chloroform spirit |

|6.0 mL |

| |

|Water for preparation |

|to 100.0 mL |

| |

|Sig; Asthma mixture 10 mL b.i.d 2/52 |

|Sig; Asthma mixture 2.5 mL bd 5/7 |

|ALLOCATE time for students to do the assignment and submit |

| |

|REFER students to recommended references |

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, Inc

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