University of Sulaimani College of Pharmacy 2nd Stage Pharmaceutical Orientation Electrolyte Solutions: Milliequivalents, Millimoles, and Milliosmoles Lecture (3) Shahen S. Mohammed

BSc Pharmacy MSc Pharmaceutics 1 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. 2 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. 3

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 mol/L are used to express the concentration of electrolytes.

4 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. 5 A milliequivalent represents the amount, in milligrams, of a solute equal to 11000 of its gram equivalent weight, taking into account the valence of the ions.

6 7 Electrolyte ions in the blood plasma include the cations Na+, K+, Ca++, and Mg++ and the anions Cl , HCO3, 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. 8 To convert milligrams (mg) to milliequivalents (mEq): mEq To convert milliequivalents (mEq) to milligrams (mg):

9 To convert milliequivalents per milliliter (mEq/mL) to milligrams per milliliter (mg/mL): mg/mL 10 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 = 11000 74.5 g = 0.0745 g = 74.5 mg 2 mEq of KCl = 74.5 mg 2 = 149 mg/mL. Or, by using the preceding equation: mg/mL = 149 mg/mL

11 What is the concentration, in grams per milliliter, of a solution containing 4 mEq of calcium chloride (CaCl22H2O) per milliliter? Formula weight of CaCl22H2O = 147 Equivalent weight of CaCl22H2O = 1472 = 73.5 1 mEq of CaCl22H2O = 11000 73.5 g = 0.0735 g 4 mEq of CaCl22H2O = 0.0735 g 4 = 0.294 g/mL

12 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 = 11000 53.5 = 0.0535 g 100 mEq of NH4Cl = 0.0535 g 100 = 5.35 g/L or 0.535 g per 100 mL, or 0.535%

13 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 = 11000 39 g = 0.039 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 = = 2.56 mEq/L 14 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 = 402 = 20

1 mEq of Ca = 11000 20 g = 0.020 g = 20 mg 10 mg/100 mL of Ca = 100 mg of Ca per liter 100 mg 20 = 5 mEq/L 15 A magnesium (Mg) level in blood plasma is determined to be 2.5 mEq/ L. Express this concentration in terms of milligrams.

16 How many milliequivalents of potassium chloride are represented in a 15-mL dose of a 10% (w/v) potassium chloride elixir? 17 How many milliequivalents of magnesium sulfate are represented in 1 g of anhydrous magnesium sulfate (MgSO4)?

18 How many milliequivalents of Na would be contained in a 30-mL dose of the following solution? Disodium hydrogen phosphate 18 g Sodium biphosphate 48 g

Purified water ad 100 mL 19 Each salt is considered separately in solving the problem. Disodium hydrogen phosphate Formula = Na2HPO4.7H2O Molecular weight = 268 and

the equivalent weight = 134 x = 5.4 g of disodium hydrogen phosphate per 30 mL 20 1 mEq = 11000 134 g = 0.134 g = 134 mg 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 21 Sodium biphosphate Formula = NaH2PO4.H2O Molecular weight = 138 and the equivalent weight = 138

x = 14.4 g of sodium biphosphate per 30 mL 1 mEq = 11000 138 g = 0.138 g = 138 mg 22 x = 104.3 mEq of sodium biphosphate and also, = 104.3 mEq of Na

Adding the two milliequivalent values for Na 40.3 mEq + 104.3 mEq =144.6 mEq. 23 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.

24 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

x = 0.725 moles = 725 mmol 25 How many milligrams would 1 mmol of monobasic sodium phosphate weigh? 1 mole = 138 g 1 mmol = 0.138 g = 138 mg

26 What is the weight, in milligrams, of 1 mmol of HPO4 ? Atomic weight of HPO4 = 95.98 1 mole of HPO4 = 95.98 g 1 mmol of HPO4 = 95.98 g = 0.09598 g = 95.98 mg 27

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.

28 29 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= No of species 1000 mOsmole/L = 1 1000 = 278 mOsmol/L 30 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= No of species 1000 mOsmol/L= 1 1000 = 40 mOsmol 31 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= No of species 1000 mOsmol/L= 1 1000 = 2.5 mOsmol 32 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= 2 1000 x = 307.7, or 308 mOsmol 33 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 + 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).

34 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

35 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. Water Requirement = 1500 mL/m2

x = 2700 mL 36 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]) +

mOsm/kg = 2 (135 mEq/L + 4.5 mEq/L) + = 2 (139.5) + 5 + 5 = 289 37 Calculate the milliequivalents of sodium, potassium and chloride, the millimoles of anhydrous dextrose, and the osmolarity of the following parenteral fluid.

Dextrose, anhydrous 50 g Sodium Chloride 4.5 g Potassium Chloride 1.49 g Water for Injection, ad 1000 mL 38

Molecular weight of NaCl = 58.5 Equivalent weight of NaCl = 58.5 1 mEq of NaCl = 1/1000 58.5 = 0.0585 g = 58.5 mg 4.5 g of NaCl = 4500 mg x = 76.9 or 77 mEq of Na and 76.9 or 77 mEq of Cl 39

Molecular weight of KCl = 74.5 Equivalent weight of KCl = 74.5 1 mEq of KCl = 1/1000 74.5 = 0.0745 g = 74.5 mg 1.49 g of KCl = 1490 mg x = 20 mEq of K and 20 mEq of Cl 40

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

X= 277.7 or 278 mmol 41 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

42 43 Thank you 44