Millequivalents and Molecular Weights

Elephant Formulary

© 2003-06 Susan K. Mikota DVM and Donald C. Plumb, Pharm.D.
Published by Elephant Care International - www.elephantcare.org

Milliequivalents & Molecular Weights

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Milliequivalents: The term milliequivalents (mEq) is usually used to express the quantities of electrolytes administered to patients. A mEq is 1/1000 of an equivalent (Eq). For pharmaceutical purposes an equivalent may be thought of as equal to the equivalent weight of a given substance. This, in practical terms, is the molecular weight of the substance divided by the valence or the radical. For example:

How many milligrams are equivalent to 1 mEq of potassium chloride (KCl)?

1. Determine the equivalent weight = gram atomic weight ÷
valence

Molecular weight of KCl = 74.5

Valence = 1 (K+; Cl-)

Equivalent weight = 74.5 ÷ 1 = 74.5 grams

2. Determine the mEq weight

Equivalent weight ÷ 1000

74.5 ÷ 1000 = 74.5 mg = 1 mEq of KCl = 1 mEq of K+ &
1 mEq of Cl-
If the substance would have been CaCl2, the process would be identical using the gram molecular weight of CaCl2 (MW 111 if anhydrous; 147 if dihydrate) and a valence of 2.

Listed below are several commonly used electrolytes with their molecular weights and valences in parentheses:

Sodium Chloride 58.44 (1) Calcium Chloride
Sodium Bicarbonate 84 (1) anhydrous 111 (2)

Sodium Acetate dihydrate 147 (2)

anhydrous 82 (1) Magnesium Sulfate

trihydrate 136 (1) heptahydrate 246.5 (2)

Sodium Lactate 112 (1) anhydrous 120.4 (2)

Potassium Chloride 74.55 (1) Magnesium Chloride

Potassium Gluconate234.25(1) anhydrous 95.21 (2)

Calcium Gluconate 430.4 (2) hexahydrate 203.3 (2)

Calcium Lactate
(anhydrous) 218.22 (2)