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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5334_Библиотеки_им_академика_М_И_Перельмана
.pdf
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c. 103.5 mg sodium chloride
4.751 g sodium chloride
44.44 g anhydrous dextrose
qs 32 mL purified water
68 mL buffered solution
13.25 mL sodium chloride solution
a. Hypotonic
b. Hypertonic
c. Isotonic
a. 28.a. 4.5%
b. 2.81%
c. 1.48%
3.67 mL purified water
26.33 mL sodium chloride solution
a. 30.a. qs 5.67 mL water
b. qs 8 mL water
c. qs 6.67 mL water
d. qs 11 mL water
e. qs 5.33 mL water
a. 31.a. 0.14
b. 0.26
c. 0.23
d. 0.22
e. 0.051
111.3 g dorzolamide hydrochloride, 34.15 g timolol maleate, 375 mg
benzalkonium chloride, 127.89 g mannitol
4.56
5.5
2.82:1
0.03 unit
8.2 g
0.18 unit
7.28
0.33 unit
References
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13.
Ingham A, Poon CY. Tonicity, osmoticity, osmolality, and osmolarity. In: Allen LV, ed.
Remington: The Science and Practice of Pharmacy, vol. 22. Philadelphia, PA: Pharmaceutical
Press; 2013:641–646.
Ansel HC, Prince SJ. Pharmaceutical Calculations: The Pharmacist’s Handbook. Baltimore,
MD: Lippincott Williams & Wilkins; 2004:111.
US Pharmacopeial Convention, Inc. General chapters. <1151> Pharmaceutical dosage forms.
United States Pharmacopeia 42 National Formulary 37 [book online]. Rockville, MD: US
Pharmacopeial Convention, Inc.; 2019.
Allen LV. Ansel’s Pharmaceutical Dosage Forms and Drug Delivery Systems. 11th Ed.
Baltimore, MD: Wolters Kluwer; 2018:469.
Titcomb LC. Topical ocular antibiotics: part 2. Pharmaceutical Journal 2000;264:441–445.
Garg P, Sharma S, Rao GN. Ciprofloxacin-resistant pseudomonas keratitis. Ophthalmology
1999;106:1319–1323.
Matoba AY. Polymicrobial keratitis secondary to Burholderia ambifaria, enterococcus, and
staphylococcus aureus in a patient with herpetic stromal keratitis. American Journal of
Ophthalmology 2003;136:748–749.
Chung MS, Goldstein MH, Driebe WT, et al. Mycobacterium chelonae keratitis after laser in
situ keratomileusis successfully treated with medical therapy and flap removal. American
Journal of Ophthalmology 2000;129: 382–384.
Chandra NS, Torres MF, Winthrop KL, et al. Cluster of Mycobacterium chelonae keratitis
cases following laser in-situ keratomileusis. American Journal of Ophthalmology
2001;132:819–830.
Ford JG, Huang AJW, Pflugfelder SC, et al. Nontuberculous mycobacterial keratitis in south
Florida. Ophthalmology 1998;105:1652–1658.
Allen LV. Tobramycin sulfate 0.3% and diclofenac sodium 0.1% ophthalmic solution.
International Journal of Pharmaceutical Compounding 2010;14:74.
US Pharmacopeial Convention, Inc. Reagents and reference tables. Buffer solutions. United
States Pharmacopeia 42 National Formulary 37 [book online]. Rockville, MD: US
Pharmacopeial Convention; 2019.
Merck & Co. Cosopt (dorzolamide hydrochloride-timolol maleate ophthalmic solution)
[product label information]. Available at:
https://www.accessdata.fda.gov/drugsatfda_docs/label/2010/020869s036lbl.pdf. Accessed
June 28, 2020.
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12
Electrolyte Solutions:
Milliequivalents, Millimoles, and
Milliosmoles
OBJECTIVES
Upon successful completion of this chapter, the student will be able
to:
Determine the molecular weight of an electrolyte from atomic or
formula weights as well as the valence and the number of ions
produced upon dissociation.
Calculate problems involving milliequivalents and apply these
principles to products used for electrolyte replacement.
Calculate problems involving millimoles and micromoles and
understand their use in pharmacy practice.
Calculate problems involving milliosmoles and osmolarity and
apply these principles to solutions primarily used for intravenous
infusions.
Introduction
As noted in Chapter 11, 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.
Electrolyte ions in the blood plasma include the cations Na+, K+,
Ca2+, and Mg2+ and the anions Cl−, HCO
3
−
, HPO
4
2−
, SO
4
2−
, organic
acids, and protein. Electrolytes in body fluids play an important role in
maintaining the acid–base balance. They also play a part in controlling
body water volumes and help regulate metabolism.
Applicable Dosage Forms
Electrolyte preparations are used in the treatment of disturbances of the
electrolyte and fluid balance in the body. They are provided by the
pharmacy as oral solutions, syrups, tablets, capsules, and, when
necessary, intravenous infusions.
Milliequivalents
A chemical unit, the milliequivalent (mEq), is used almost exclusively in
the United States by clinicians, physicians, pharmacists, and
manufacturers to express the concentration of electrolytes in solution.
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. In other words, it is a
unit of measurement of the amount of chemical activity of an electrolyte.
Under normal conditions, blood plasma contains 154 mEq of cations
and an equal number of anions (Table 12.1). However, it should be
understood that normal laboratory values of electrolytes vary, albeit
within a rather narrow range, as shown in Table 12.2. 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−, HCO
3
−
, or any
anion. For a given chemical compound, the milliequivalents of cation
equal the milliequivalents of anion equal the milliequivalents of the
chemical compound.
TABLE 12.1 BLOOD PLASMA ELECTROLYTES IN
MILLIEQUIVALENTS PER LITER (mEq/L)
TABLE 12.2 USUAL REFERENCE RANGE OF BLOOD
SERUM VALUES FOR SOME ELECTROLYTES
a
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a
Reference ranges may vary slightly between clinical laboratories based,
in part, on the analytical methods and equipment used.
In preparing a solution of K+ ions, a potassium salt is dissolved in water.
In addition to the K+ ions, the solution will also contain negatively
charged ions. These two components will be chemically equal, in that the
milliequivalents of one are equal to the milliequivalents of the other.
Dissolving 40 mEq of potassium chloride in water results in a solution
that contains 40 mEq of K+ per liter and 40 mEq of Cl−. Interestingly, the
solution will not contain the same weight of each ion.
A milliequivalent represents the amount, in milligrams, of a solute
equal to one-thousandth of its gram equivalent weight, taking into
account the valence of the ions. The milliequivalent expresses the
chemical activity or combining power of a substance relative to the
activity of 1 mg of hydrogen. Thus, based on the atomic weight and
valence of the species, 1 mEq is represented by 1 mg of hydrogen, 20 mg
of calcium, 23 mg of sodium, 35.5 mg of chlorine, 39 mg of potassium,
and so forth.
A key element in converting between the weight of an electrolyte
(i.e., milligrams) and its chemical activity (i.e., milliequivalents) is the
valence of the substance, and the total valence of the cation or anion in
the compound must be taken into account. Sodium chloride, for example,
has a total valence of one because there is one sodium cation with a +1
charge and one chloride anion with a −1 charge in the compound.
However, sodium citrate has a total valence of three because there are
three sodium ions with a +1 charge (for a total of +3) and one citrate ion
with a −3 charge. Knowing the valence of various compounds is essential
in the calculation of milliequivalents. Important values for some ions are
presented in Table 12.3, and a complete listing of atomic weights is
provided in Appendix C.
TABLE 12.3 VALUES FOR SOME IMPORTANT IONS
a
Example calculations of milliequivalents
The following conversion can be used to convert milligrams to
milliequivalents and vice versa:
1. A physician prescribes 10 mEq of potassium chloride for a patient.
How many milligrams of KCl would provide the prescribed
quantity?
2. If a patient is prescribed 300 mg of potassium chloride, what is the
corresponding mEq?
See example problem 1 for molecular weight and conversion for
KCl.
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3. A physician prescribes 3 mEq/kg of NaCl to be administered to a 165lb patient. How many milliliters of a half–normal saline solution
(0.45% NaCl) should be administered?
4. What is the concentration, in milligrams per milliliter, of a solution
containing 2 mEq of potassium chloride (KCl) per milliliter?
See example problem 1 for molecular weight and conversion for
KCl.
5. What is the concentration, in grams per milliliter, of a solution
containing 4 mEq of calcium chloride (CaCl2 · 2H2O) per milliliter?
NOTE: The water of hydration molecules should be accounted for in
the molecular weight but does not interfere in determination of
valence.
6. What is the percent (w/v) concentration of a solution containing 100
mEq of ammonium chloride per liter?
7. A solution contains 10 mg/100 mL of K+ ions. Express this
concentration in terms of milliequivalents per liter.
8. A solution contains 10 mg/100 mL of Ca2+ ions. Express this
concentration in terms of milliequivalents per liter.
9. A magnesium (Mg2+) level in blood plasma is determined to be 2.5
mEq/L. Express this concentration in terms of milligrams per liter.
10. An aluminum hydroxide gel suspension contains 320 mg of
aluminum hydroxide in each teaspoonful dose. How many
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milliequivalents of aluminum would a patient receive each day if he
is ingesting two teaspoonfuls of the suspension four times daily?
11. How many milliequivalents of magnesium are represented in an 8mL dose of an injectable solution containing 50% w/v magnesium
sulfate heptahydrate?
12. How many milliequivalents of Na+ would be contained in a 30-mL
dose of the following solution?
Each salt is considered separately in solving the problem.
Sodium phosphate, dibasic, heptahydrate:
Sodium phosphate, monobasic, monohydrate:
CASE IN POINT 12.1
A
A hospital pharmacist receives a medication order calling for 10 mEq
of calcium to be added to a 500-mL bag of normal saline solution. The
intravenous fluid is to be administered at a rate of 0.5 mEq of calcium
per hour. The pharmacist has available 10-mL vials of a 10% injection
of calcium chloride dihydrate. (a) How many milliliters of this
injection should be added to the bag of IV fluid to make the desired
product? (b) If the nurse administering the IV fluid uses an intravenous
set that delivers 12 drops/mL, how many drops per minute should be
delivered to provide the desired dose?
a
Problem courtesy of Flynn Warren, Bishop, GA.
CASE IN POINT 12.2
A patient is to receive 0.12 mEq of ferrous gluconate per kilogram of
body weight each day divided into three doses. (a) If the patient
weighs 132 lb, how many milliliters of a compounded syrup
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