NTA Level 5 • Semester 2 • PST05208

Calculations Involving Milliosmoles (mOsmol)

Pharmaceutics Theory and Compounding • Source Session/Topic 17

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Session 17: Calculations Involving Milliosmoles (mOsmol)

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:

• Give introduction to calculations involving milliosmoles

• Perform calculations Involving Milliosmoles

Resources Needed:

• Flip charts, marker pens, and masking tape

• Black/white board, chalk and whiteboard markers

• LCD projector and compute

SESSION OVERVIEW

Activity/

Step Time Content

Method

1 05 Minutes Presentation Introduction, Learning Tasks

45 Minutes Introduction to Calculations Involving

2 Presentation Milliosmoles

60 Minutes Presentation Performing Calculation Involving Milliosmoles

Demonstration

4 05 Minutes Presentation Key Points

5 05 Minutes Presentation Evaluation

120

SESSION CONTENTS

STEP1: 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: Introduction to Milliosmoles (45 minutes)

• The osmotic activity of a solution may be stated in terms of Milliosmoles which is an expression

of the osmotic activity of 1 Millimole

• The term Osmolarity is used to express the strength in mOsmol per liter and indicates the total

ionic concentration of the solution

• Labels of some pharmacopoeia solutions that provide intravenous replenishment of fluids,

nutrients, electrolytes and the osmotic diuretic mannitol are required to state osmolar

concentration.

• This information indicates to the practitioner whether the solution is hypotonic, isotonic or

hypertonic with regard to biologic fluids and membranes

• Since the unit that is used to measure osmotic concentration is Milliosmoles then;

o For non – electrolytes e.g. dextrose 1 mmol (formulary weight in mg) represents

1 mOsmol

o For electrolytes, the total number of particles in solution depends on the degree of

dissociation of the substance in question, assuming complete dissociation

• 1 mmol of NaCl represents 2 mOsmol ( Na+ and Cl-) of the total particles

• 1 mmol of CaCl2 represents 3 mOsmol ( Ca2+ and 2Cl-) of the total particles

• 1 mmol of Sodium citrate (Na3C6H5O7) represents 4 mOsmol ( 3Na+ -C6H5O7) of the total

particles

• The milliosmolar value of separate ion of an electrolyte may be obtained by dividing the

concentration in mg per liter of an ion by its atomic weight

• The milliosmolar value of the whole electrolyte in solution is equal to the sum of the milliosmolar

value of separate ions

• According to USP, the ideal osmolar concentration may be calculated using the following

equation:

• mOsmol/L = Weight of the substance(in g/L) x Number of specie x 1000

Molecular weight (in g)

121

• Examples

o A solution contains 5% anhydrous dextrose in water for injection. How many mOsmol per

liter are represented by this concentration?

o Formula weight of anhydrous dextrose = 180

o 1mmol of anhydrous dextrose (= 180 mg) = 1 mosmol

o 5% solution contains 50g or 50,000mg/L

o Therefore:

 mOsmol/L = 50,000 = 278mOsmol/

180

 OR Using USP equation:

 mOsmol/L = 50 x 1000 = 278 mOsmol/ L

o 180

STEP 3: Performing Calculations Involving Milliosmoles (60 Minutes)

Activity: Small Group Discussion ( 40 minutes)

DIVIDE students in small manageable groups

ASK students to discuss in groups on the following questions

• How many mOsmol are represented in a liter of a 0.9% sodium chloride solution

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

Formula weight of NaCl = 58.5

1 mmol of NaCl (= 58.5mg) = 2 mOsmol

900mg of NaCl per 100mL = 9000mg NaCl per liter

Then by using proportion:

58.5mg = 2mOsmol x = 9000 x 2

9000mg x mOsmol 58.5

X = 307.7 = 308mOsmol/

122

STEP 4: Key Points (5 minutes)

• Milliosmoles (mOsmol) is an expression of the osmotic activity of 1 Millimole

• The osmotic activity of a solution may be stated in terms of Milliosmoles which is an expression

of the osmotic activity of 1 Millimole

• The term Osmolarity is used to express the strength in mOsmol per liter and indicates the total

ionic concentration of the solution

• This information indicates to the practitioner whether the solution is hypotonic, isotonic or

hypertonic with regard to biologic fluids and membranes

STEP 5: Evaluation (5 minutes)

• What is Milliosmoles?

• What are the uses of Osmolarity?

STEP 6: Take Home Assignment (15 Minutes)

Activity: Take home Assignment (15 minutes)

ASK each individual student to do the following assignment

• A solution contains 156mg of k+ ions per 100 mL. How many mOsmol are represented

in a liter of the solution?

ALLOCATE time for students to do the assignment and submit

REFER students to recommended references

123

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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