NTA Level 5 • Semester 2 • PST05208

Calculations Involving Milliequivalent

Pharmaceutics Theory and Compounding • Source Session/Topic 15

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Session 15: Calculations Involving Milliequivalent

Total Session Time: 120 minutes + 6 hours of Practices

Prerequisites

• None

Learning Tasks

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

• Explain Milliequivalent

• Calculate Milliequivalent

Resources Needed:

• Flip charts, marker pens, and masking tape

• Black/white board, chalk and whiteboard markers

• LCD projector and computer

• Handout 15.1: Values for some important ions

SESSION OVERVIEW

Activity/

Step Time Content

Method

1 05 minutes Presentation Introduction, Learning Tasks

2 45minutes Presentation Milliequivalent

60 minutes Presentation Calculating Milliequivalent

Demonstration

4 05 minutes Presentation Key Points

5 05 minutes Presentation Evaluation

108

SESSION CONTENTS

STEP1: Presentation of Session Title and Learning Tasks (05 Minutes)

READ or ASK students to read the learning tasks and clarify

ASK students if they have any questions before continuing

STEP 2: Milliequivalent (45 Minutes)

• The equivalent weight of an element is the gram atomic weight divided by its valency OR

• A Milliequivalent of an ion is the ionic weight in mg divided by the valence of that ion

• Divide the Equivalent by 1000, and you get a

• For example, Na has an atomic weight of 23. So 23 mg of Na+ in solution means 1 mmol of Na+

is in solution. We could also say 1 mEq of Na+ is in solution.

• Ca has an atomic weight of 40. So 40 mg of Ca2+ in solution means 1 mmol of Ca2+ is in solution.

In this case, 2 mEq of Ca is in solution.

1mEq = ionic weight in mg e.g. 1mEqCa2+ = 40 = 20mg

Valency 2

1mEqCa is equivalent to 20mg calcium

The number of mEq of each ion obtained from a salt in solution therefore depends on the valency

of the ion e. g. Sodium chloride has 1 Na+ and Cl- in each molecule and both have the valency of

one

1mEq Na+ = 23 = 23mg sodium

1mEq Cl = 35. 5 = 35.5mg sodium

Therefore, 58.5mg sodium chloride provide 1 mEq Na+ and 1 mEq Cl-

• In this case mmol and mEq give numerically the same results, because both ions have the valency

of one

CaCl2 2H2O provides 1 Ca2+ which has the valency of two and Cl- with the valency of one

1mEqCa2+ = 40 = 20mg calcium

–

1mEqCl = 35 = 35.5mg chloride

109

Hence 147mg CaCl2.2H2O will provide 2mEq Ca2+ and 2 mEq Cl;

(20 x 2) + (35.5 x 2) + (18 x 2) = 147

N.B: The molecular weight of H2O is 18

• Therefore, the amount of salt containing 1 mEq of specified ion is calculated by the following

equation:

• Mg salt containing 1 mEq of specified ion = molecular weight of salt

Valency of specified ion x number of specified ions in the

molecule

• E.g. How many mg of calcium chloride are needed to provide 1mEq of Ca2+ and 1 mEq Cl?

• MgCaCl2.2H2O containing 1mEq of Ca2+ = 147 = 73.5mg

2×1

• MgCaCl2.2H2O containing 1mEq of Cl = 147 = 73.5mg

–

2×1

•

73.5mg CaCl2 .2H2O provide 1mEq Ca and 1 mEq Cl-

• When g or mg salt are stated the number of mEq can be calculated by simple proportion

e.g. How many mEq Na+ are contained in 351mg NaCl?

1 = x x = 1 x 351 = 6mEq

58.5 351 58.5

• The number of mEq of anions cations in any amount of salt is always the same, whereas the

number of mmol of anions and cations differs with certain salts, depending on the number of ions

in the molecule

• Conversion of mmol to mEq and vice versa can be done by the following equation:

Mmol == mEq

Valency

Examples

• Molecular weights can be obtained from the table below

1. How many mg of sodium phosphate contain 1mEq HPO42-

Mg Na2HPO4.12H2O containing 1mEq HPO42- = 358 = 179mg

2X1

179mg ofNa2HPO4.12H2O provide 1mEq HPO4

• According to the note above, 179mg of the salt will provide as well 1mEq Na+

2. A solution contains 90 mEq Na+, 60mEq K+ and 150 mEq Cl- per litre. Convert to g/L

• A convenient way to solve the question is first to arrange the mEq in a table, so that the

composition of the salt is obvious

110

Cations Anions

Na+ K +

Cl-

90 90

60 60

150 150

NaCl: As 1 mEq Na+ or Cl- is provided by 58.5mg NaCl, then 90mEq will be provided by

58.5 x 90

58.5x 90 = 5265mg

KCL: The amount is found respectively

74.5 x 60 = 4470mg

Therefore the solution contains 5.265g NaCl and 4.47g KCL per litre

STEP 3: Calculating Milliequivalent (60 minutes)

Activity: Small Group Discussion ( 30 minutes)

DIVIDE students in small manageable groups

ASK students to discuss in groups on the following questions

• 367mg calcium chloride provide how many mmol Ca2+ and how many mmol Cl-?

REFER Students to Pharmaceutical Calculation. 13th Edition by HOWARD C.

ANSEL: Chapter 11,for reference

ALLOW students to discuss for 20 minutes

ALLOW each groups to present for 5 minutes

CLARIFY and SUMMARIZE by using the contents below

1mmol Ca2+ = 147 == 147mg

111

Therefore: 1 = x x = 1 x 367 = 2.49 = 2.5 mmol Ca2+

147 367, 147

1mmol Cl- = 147mg = 73.5mg

Therefore:

1 = x x = 1 x 367 = 4.99 = 5mmol Cl-

73.5 367 73.5

367mg calcium chloride provide 2.5mmol Ca2+ and 5 mmol Cl-

Handout 15.1: Values for some important ions

STEP 4: Key Points (5 minutes)

• A Milliequivalent of an ion is the ionic weight in mg divided by the valence of that ion

• The number of mEq of anions cations in any amount of salt is always the same, whereas the

number of mmol of anions and cations differs with certain salts, depending on the number of ions

in the molecules

STEP 5: Evaluation (5 minutes)

• What is equivalent weight of an element?

• What is Millequivalent?

STEP 6: Take Home Assignment (15 minutes)

Activity: Take home Assignment (15 minutes)

ASK each individual student to do the following assignment

• Calculate the strength of sodium chloride solution which is iso – osmotic with blood

serum and tears

ALLOCATE time for students to do the assignment and submit

REFER students to recommended references

112

Handout 15.1: Values for some important ions

113

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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