1. Electrolyte Solutions: Milliequivalents, Millimoles, and Milliosmoles
University of Sulaimani College of Pharmacy 2nd Stage Pharmaceutical Orientation
Electrolyte Solutions: Milliequivalents,
Millimoles, and Milliosmoles
Lecture (4)
Shahen S. Mohammed
BSc Pharmacy
MSc Pharmaceutics

2. Electrolyte Solutions
The molecules of chemical compounds in solution may remain intact, or they may dissociate into particles known as ions, which carry an electric charge.
Substances that are not dissociated in solution are called nonelectrolytes, and those with varying degrees of dissociation are called electrolytes.
Urea and dextrose are examples of nonelectrolytes in body water; sodium chloride in body fluids is an example of an electrolyte.

3. Electrolyte Solutions
Applicable Dosage Forms
Electrolyte preparations are used in the treatment of disturbances of the electrolyte and fluid balance in the body.
In clinical practice, they are provided in the form of oral solutions and syrups, as dry granules intended to be dissolved in water or juice to make an oral solution, as oral tablets and capsules and, when necessary, as intravenous infusions.

4. Milliequivalents(mEq)
Is a chemical unit, used to express the concentration of electrolytes in solution. In other words, it is a unit of measurement of the amount of chemical activity of an electrolyte.
This unit of measure is related to the total number of ionic charges in solution, and it takes note of the valence of the ions.
mEq, mmol/L, and µmol/L are used to express the concentration of electrolytes.

5. Milliequivalents
The total concentration of cations always equals the total concentration of anions.
Any number of milliequivalents of Na +, K +, or any cation always reacts with precisely the same number of milliequivalents of Cl¯, HCO3¯ , or any anion.
For a given chemical compound, the milliequivalents of cation equals the milliequivalents of anion equals the milliequivalents of the chemical compound.

6. A milliequivalent represents the amount, in milligrams, of a solute equal to 1⁄1000 of its gram equivalent weight, taking into account the valence of the ions.

8. Electrolyte ions in the blood plasma include the cations Na+, K+, Ca++, and Mg++ and the anions Cl¯ , HCO¯3, HPO¯¯ 4 , SO ¯¯4 , organic acids, and protein.
Electrolytes in body fluids play an important role in maintaining the acid-base balance in the body. They play a part in controlling body water volumes and help to regulate body metabolism.

9. To convert milligrams (mg) to milliequivalents (mEq):
mEq = mg × Valence Atomic, formular, or molecular weight
To convert milliequivalents (mEq) to milligrams (mg):
mg = mEq×Atomic, formula, or molecular weight Valence

10. mg/mL = mEq/mL × Atomic, formula, or molecular weight Valence
To convert milliequivalents per milliliter (mEq/mL) to milligrams per milliliter (mg/mL):
mg/mL = mEq/mL × Atomic, formula, or molecular weight Valence

11. Example Calculations of Milliequivalents
What is the concentration, in milligrams per milliliter, of a solution containing 2 mEq of potassium chloride (KCl) per milliliter?
Molecular weight of KCl = 74.5
Equivalent weight of KCl = 74.5
1 mEq of KCl = 1⁄1000 × 74.5 g = g = 74.5 mg
2 mEq of KCl = 74.5 mg × 2 = 149 mg/mL.
Or, by using the preceding equation:
mg/mL = 2 (mEq/mL)× = 149 mg/mL

12. Formula weight of CaCl2⋅2H2O = 147
What is the concentration, in grams per milliliter, of a solution containing 4 mEq of calcium chloride (CaCl2⋅2H2O) per milliliter?
Formula weight of CaCl2⋅2H2O = 147
Equivalent weight of CaCl2⋅2H2O = 147⁄2 = 73.5
1 mEq of CaCl2⋅2H2O = 1⁄1000 × 73.5 g = g
4 mEq of CaCl2⋅2H2O = g × 4 = g/mL

13. Molecular weight of NH4Cl = 53.5 Equivalent weight of NH4Cl = 53.5
What is the percent (w/v) concentration of a solution containing 100 mEq of ammonium chloride per liter?
Molecular weight of NH4Cl = 53.5
Equivalent weight of NH4Cl = 53.5
1 mEq of NH4Cl = 1⁄1000 × 53.5 = g
100 mEq of NH4Cl = g × 100 = 5.35 g/L or
0.535 g per 100 mL, or 0.535%

14. Equivalent weight of K = 39
A solution contains 10 mg/100 mL of K ions. Express this concentration in terms of milliequivalents per liter.
Atomic weight of K+ = 39
Equivalent weight of K = 39
1 mEq of K = 1⁄1000 × 39 g = g = 39 mg
10 mg/100 mL of K = 100 mg of K per liter
100 mg ÷ 39 = 2.56 mEq/L
Or by the equation,
mEq/L = (mg/L) × = 2.56 mEq/L

15. Equivalent weight of Ca = 40⁄2 = 20
A solution contains 10 mg/100 mL of Ca ions. Express this concentration in terms of milliequivalents per liter.
Atomic weight of Ca++ = 40
Equivalent weight of Ca = 40⁄2 = 20
1 mEq of Ca = 1⁄1000 × 20 g = g = 20 mg
10 mg/100 mL of Ca = 100 mg of Ca per liter
100 mg ÷ 20 = 5 mEq/L

16. A magnesium (Mg) level in blood plasma is determined to be 2. 5 mEq/L
A magnesium (Mg) level in blood plasma is determined to be 2.5 mEq/L. Express this concentration in terms of milligrams.

17. How many milliequivalents of potassium chloride are represented in a 15-mL dose of a 10% (w/v) potassium chloride elixir?

18. How many milliequivalents of magnesium sulfate are represented in 1 g of anhydrous magnesium sulfate (MgSO4)?

19. How many milliequivalents of Na would be contained in a 30-mL dose of the following solution?
Disodium hydrogen phosphate g
Sodium biphosphate g
Purified water ad mL

20. Each salt is considered separately in solving the problem.
Disodium hydrogen phosphate
Formula = Na2HPO4.7H2O
Molecular weight = 268 and
the equivalent weight = 134
18 (g) x (g) = 100 (mL) 30 (mL)
x = 5.4 g of disodium hydrogen phosphate per 30 mL

21. x = 40.3 mEq of disodium hydrogen phosphate
1 mEq = 1⁄1000 × 134 g = g = 134 mg
134 (mg) 5400 (mg) = 1 (mEq) x (mEq)
x = 40.3 mEq of disodium hydrogen phosphate
Because the milliequivalent value of Na ion equals the milliequivalent value of disodium hydrogen phosphate, then
x = 40.3 mEq of Na

22. Sodium biphosphate Formula = NaH2PO4
Sodium biphosphate Formula = NaH2PO4.H2O Molecular weight = 138 and the equivalent weight = (g) x (g) = 100 (mL) 30 (mL) x = 14.4 g of sodium biphosphate per 30 mL 1 mEq = 1⁄1000 × 138 g = g = 138 mg

23. 138 (mg) 14,400 (mg) = 1 (mEq) x (mEq) x = 104
138 (mg) 14,400 (mg) = 1 (mEq) x (mEq) x = mEq of sodium biphosphate and also, = mEq of Na Adding the two milliequivalent values for Na 40.3 mEq mEq =144.6 mEq.

24. Millimoles and Micromoles
A mole is the molecular weight of a substance in grams.
A millimole is one thousandth of a mole and
A micromole is one millionth of a mole.

25. Example Calculations of Millimoles and Micromoles
How many millimoles of monobasic sodium phosphate (m.w. 138) are present in 100 g of the substance?
m.w. = 138
1 mole = 138 g
1 (mole) x (mole) = 138 (g) 100 (g)
x = moles = 725 mmol

26. How many milligrams would 1 mmol of monobasic sodium phosphate weigh?
1 mole = 138 g
1 mmol = g = 138 mg

27. What is the weight, in milligrams, of 1 mmol of HPO4 ?
Atomic weight of HPO4 = 95.98
1 mole of HPO4 = g
1 mmol of HPO4 = g × = g
= mg

28. Osmolarity
Osmolarity is the milliosmoles of solute per liter of solution
Osmolality is the milliosmoles of solute per kilogram of solvent.
For dilute aqueous solutions, osmolarity and osmolality are nearly identical.
For more concentrated solutions, however, the two values may be quite dissimilar.
Osmometers are commercially available for use in the laboratory to measure osmolality.

30. Example Calculations of Milliosmoles??
A solution contains 5% of anhydrous dextrose in water for injection. How many milliosmoles per liter are represented by this concentration?
Formula weight of anhydrous dextrose = 180
mOsmol/L= 𝑾𝒆𝒊𝒈𝒉𝒕 𝒐𝒇 𝑺𝒖𝒃𝒔𝒕𝒂𝒄𝒆 ( 𝒈 𝑳 ) 𝑴𝒐𝒍𝒆𝒄𝒖𝒍𝒂𝒓 𝒘𝒆𝒊𝒈𝒉𝒕 (𝒈) × No of species × 1000
mOsmole/L = 𝟓𝟎 𝒈/𝑳 𝟏𝟖𝟎(𝒈) × 1 ×1000
= 278 mOsmol/L

31. A solution contains 156 mg of K ions per 100 mL
A solution contains 156 mg of K ions per 100 mL. How many milliosmoles are represented in a liter of the solution?
Atomic weight of K = 39
mOsmol/L= 𝑾𝒆𝒊𝒈𝒉𝒕 𝒐𝒇 𝑺𝒖𝒃𝒔𝒕𝒂𝒄𝒆 ( 𝒈 𝑳 ) 𝑴𝒐𝒍𝒆𝒄𝒖𝒍𝒂𝒓 𝒘𝒆𝒊𝒈𝒉𝒕 (𝒈) × No of species × 1000
mOsmol/L= 𝟏.𝟓𝟔( 𝒈 𝑳 ) 𝟑𝟗(𝒈) × 1× 1000
= 40 mOsmol

32. A solution contains 10 mg% of Ca ions
A solution contains 10 mg% of Ca ions. How many milliosmoles are represented in 1 liter of the solution?
Atomic weight of Ca = 40
mOsmol/L= 𝑾𝒆𝒊𝒈𝒉𝒕 𝒐𝒇 𝑺𝒖𝒃𝒔𝒕𝒂𝒄𝒆 ( 𝒈 𝑳 ) 𝑴𝒐𝒍𝒆𝒄𝒖𝒍𝒂𝒓 𝒘𝒆𝒊𝒈𝒉𝒕 (𝒈) × No of species × 1000
mOsmol/L= 𝟎.𝟏( 𝒈 𝑳 ) 𝟒𝟎(𝒈) × 1× 1000
= 2.5 mOsmol

33. Formula weight of NaCl = 58.5
How many milliosmoles are represented in a liter of a 0.9% sodium chloride solution?
1 mmol of sodium chloride (NaCl) represents 2 mOsmol of total particles (Na + Cl).
Formula weight of NaCl = 58.5
mOsmol/L= 𝟗( 𝒈 𝑳 ) 𝟕𝟒.𝟓(𝒈) × 2× 1000
x = 307.7, or 308 mOsmol

34. Clinical Considerations of Water and Electrolyte Balance
cell membranes generally are freely permeable to water, the osmolality of the extracellular fluid (about 290 mOsm/kg water) is about equal to that of the intracellular fluid. Therefore, the plasma osmolality is a convenient and accurate guide to intracellular osmolality and may be approximated by the formula
Plasma osmolality (mOsm/kg) = 2 ([Na] + [K]) plasma + [BUN] [Glucose] 18
where: sodium (Na) and potassium (K) are in mEq/L, and blood urea nitrogen (BUN) and glucose concentrations are in mg/100 mL , (mg/dL).

35. This clinical calculations include the
determination of body water requirement,
estimation of plasma osmolality, and
calculation of the osmolality and
milliequivalent content of physiologic electrolyte solutions

36. Example Calculations of Water Requirements and Electrolytes in Parenteral Fluids
Calculate the estimated daily water requirement for a healthy adult with a body surface area of 1.8 m2.
1m2 1.8 m2 = mL x mL
x = 2700 mL
Water Requirement = 1500 mL/m2

37. mOsm/kg = 2 ([Na] + [K]) + [BUN] 2.8 + [Glucose] 18
Estimate the plasma osmolality from the following data: sodium, 135 mEq/L; potassium, 4.5 mEq/L; blood urea nitrogen, 14 mg/dL; and glucose, 90 mg/dL.
mOsm/kg = 2 ([Na] + [K]) + [BUN] [Glucose] 18
mOsm/kg = 2 (135 mEq/L mEq/L) mg/dL mg/dL 18
= 2 (139.5)
= 289

38. Calculate the milliequivalents of sodium, potassium and chloride, the millimoles of anhydrous dextrose, and the osmolarity of the following parenteral fluid.
Dextrose, anhydrous g
Sodium Chloride g
Potassium Chloride g
Water for Injection, ad mL

39. Molecular weight of NaCl = 58. 5 Equivalent weight of NaCl = 58
Molecular weight of NaCl = 58.5 Equivalent weight of NaCl = mEq of NaCl = 1/1000 × 58.5 = g = 58.5 mg 4.5 g of NaCl = 4500 mg 58.5 mg 4500 mg = 1 mEq x mEq x = 76.9 or 77 mEq of Na and 76.9 or 77 mEq of Cl

40. Molecular weight of KCl = 74. 5 Equivalent weight of KCl = 74
Molecular weight of KCl = 74.5 Equivalent weight of KCl = mEq of KCl = 1/1000 × 74.5 = g = 74.5 mg 1.49 g of KCl = 1490 mg 74.5 mg 1490 = 1 mEq x mEq x = 20 mEq of K and 20 mEq of Cl

41. Total: Na = 77 mEq K = 20 mEq Cl = 77 mEq + 20 mEq = 97 mEq Molecular weight of anhydrous dextrose = mmol of anhydrous dextrose = 180 mg 50 g of anhydrous dextrose = 50,000 mg 180 mg 50,000 mg = 1 mmol x mmol X= or 278 mmol

42. Osmolarity: Dextrose, anhyd
Osmolarity: Dextrose, anhyd.: 278 mmol × 1 particle per mmol = 278 mOsmol NaCl: 77 mEq × 2 particles per mEq (or mmol) = 154 mOsmol KCl: 20 mEq × 2 particles per mEq (or mmol) = 40 mOsmol Total = 472 mOsmol