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THE OBJECTIVES INCLUDE THE
FOLLOWING:
2016 ANNUAL MEETING
PHARMACY CALCULATIONS
• Discuss importance of calculations in a pharmacy practice.
• Outline steps to avoid calculation errors
• Explain importance of reading the prescription carefully then
performing calculations
• Explain importance of calculations in determining days supply
• Describe consequences of calculation errors.
• Perform calculations during the presentation
2016 ANNUAL MEETING
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ADDITIONAL LEARNING OBJECTIVES
2016 ANNUAL MEETING
SUNIL S. JAMBHEKAR, B. PHARM.; M.S., PH.D
PROFESSOR, PHARMACEUTICAL SCIENCES
LECOM BRADENTON, SCHOOL OF PHARMACY
BRADENTON, FL34202
[email protected]
•Understand how the concentration of electrolyte
solutions are expressed and calculations of m.Eq.
•Understand the importance of iso-tonicity in
ophthalmic solutions.
•Perform calculations, using a prescription, to
determine the quantity of a liquid product required
to fill the prescription accurately.
2016 ANNUAL MEETING
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ADDITIONAL LEARNING OBJECTIVES
2016 ANNUAL MEETING
DISCLOSURE
I DO NOT HAVE A VESTED INTEREST IN OR AFFILIATION
WITH ANY CORPORATE ORGANIZATION OFFERING FINANCIAL
SUPPORT OR GRANT MONIES FOR THIS CONTINUING
EDUCATION ACTIVITY, OR ANY AFFILIATION WITH AN
ORGANIZATION WHOSE PHILOSOPHY COULD POTENTIALLY
BIAS MY PRESENTATION
•Perform calculations, using a prescription, to
determine the # of day supply for a specific
product.
•Perform calculations to determine m.Eq
strength of an electrolyte solution.
•Perform calculations to prepare an isotonic
ophthalmic solution.
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7/7/2016
IMPORTANCE OF CALCULATIONS IN
THE PHARMACY PRACTICE:
•It is consistent with the practice and philosophy
of pharmaceutical care.
•Patient safety is of utmost importance.
•Your pharmacy is the last check point for the
prescription written by a physician. Therefore,
pharmacy team is responsible for all the final
checks.
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•The final check points will include
•accuracy of the dose and dosage regimen;
•the quantity prescribed or required;
•# of refills; and # of days supply.
•Your Pharmacists depend on you to input the
prescription accurately to avoid editing and
save time.
•Insurance companies will reimburse you or
your employer only for the quantity written on
the prescription and not for the quantity
dispensed.
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Electrolytes Concentration
Its solution contains ions.
Examples include,
sodium chloride, calcium chloride, potassium chloride,
zinc sulfate, magnesium sulfate, and many more.
Electrolytes dissociate into particles known as ions. For
example,
NaCl ------ Na+ (cation) + Cl- (anion)
These ions carry electric charge
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•The internal and external audit is another good
reason for maintaining accuracy of the
prescription.
•Federal and state regulations will also play an
important role.
•When there is a reimbursement issue, accuracy
in the quantity of the medication dispensed
becomes an important matter.
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Electrolyte ions (cations) commonly present in the blood
include:
sodium (Na+), potassium (K+), calcium (Ca++),
magnesium (Mg++), etc.
The anions commonly found in the blood are Chloride
(Cl-), bicarbonate (HCO3--), phosphate (HPO4--), and
sulfate (SO4--).
These ions maintain acid-base balance in the body.
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•Electrolyte solutions are, therefore, used in the treatment
For example: Potassium chloride (KCl)
Molecular weight = 74.5 grams
of disturbances in the electrolytes.
•The concentrations of these solutions can be can be
Equivalent weight = 74.5 grams
expressed as % W/V or mg %; however, these expressions
do not take into consideration chemical equivalence and,
hence, they do not give any direct information as to the
number ions or charges they carry.
• A chemical unit, mili-equivalent (m.Eq.) is almost
Potassium (K+) = 39 grams and chloride (Cl-) = 35.5
grams
Therefore, 39 + 35.5 = 74.5 grams
74.5/1000 = 0.0745 grams or 74.5 mgs
exclusively used to express the concentration of an
electrolyte in solution.
Therefore, 74.5 milligrams of KCl = 1 m.Eq of KCl
149 milligrams of KCl = 2 m.Eq of KCl
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For Calcium Chloride (CaCl2.2H2O)
•This unit is related to the number of ionic charges in
solution and the valence of ions or m.Eq unit is a
measurement of the amount of chemical activity of an
electrolyte.
• Under normal conditions, blood plasma contains 155
m.Eq of cations and same number of anions.
•The total concentration of cations always equals the total
concentration of anions.
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Molecular weight = 147 grams
Its equivalent weight is
= Molecular weight/total valence (2)
Equivalent weight = 147/2 = 73.5 grams and 73.5
grams/1000 = 0.0735 grams or 73.5 mgs.
Therefore, 73.5 mg of calcium chloride represent 1 mEq
of calcium chloride (CaCl2.2H2O) and 147.0 mg of
calcium chloride (CaCl2.2H2O) represent 2 m.Eq of
calcium chloride
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The expression mEq represents the amount of solute in
mg equal to 1/1000 th gram of the equivalent weight of
the substance.
Equivalent weight (grams)
1 mEq =
Two Tables in your handout provide values for some
important cations and anions.
---------------------------------1000
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Ions
Valence
At. weight
mEq. (mg)
Na+
K+
Ca++
Mg++
NH4+
Li+
1
1
2
2
1
1
23
39
40
24
18
7
23
39
20
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• Patient will need 74.5 mg/mEq. x 15 mEq. X 2/day
= 2235 mg of potassium chloride daily
• Potassium chloride is available as 10% w/v (i.e., 10
g/100 ml or 10,000 mg/100 mL) or 100 mg/mL
• 100 mg of KCl is provided by 1 mL of 10% w/v
potassium chloride solution
• 1117.5 mg (15 mEq.) will be provided by X mL of
solution
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Ions
Valence
At. weight
mEq. (mg)
Cl-
1
2
1
2
1
2
35.5
96.0
61.0
60.0
97.0
96.0
35.5
48.0
61.0
30.0
97.0
48.0
SO4- HCO3CO3- H2PO4HPO4- -
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• 1117.5 mg/100 mg/mL =
11.175 mL of 10% w/v solution will provide 15
mEq. of potassium chloride
• 11.175 mL x 2/day = 22.35 mL per day x 21 days =
469.35 ml quantity for 3 weeks
• Sig: 11.175 ml by mouth twice a day for three
weeks
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POTASSIUM CHLORIDE PRESCRIPTION
Isotonic Solution
Potassium chloride liquid
A solution that has same osmotic pressure as body fluids.
Sig: 15 mEq;po;bid;for 3 weeks
Dis; QS
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Hypotonic Solution
Refill x2
Potassium chloride is available as 10% w/v solution
A solution that has lower osmotic pressure than the body
fluid.
Molecular weight of potassium chloride is 74.5 grams
Hypertonic Solution
Therefore 74.5 mg (Molecular weight in milligrams is
equal to 1 mEq. for monovalent compounds)
A solution that has higher osmotic pressure than that of
body fluids.
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• It has been determined that 0.9% w/v solution of
sodium chloride exhibits same osmotic pressure as the
human body fluids
• Therefore, while preparing solution to be administered
in the body (ophthalmic solution and intravenous
solutions), it is imperative that these solutions have
same osmotic pressure as body fluid or as 0.9% sodium
chloride solution.
• Therefore, most frequently, sodium chloride is used to
make solution isotonic. Boric acid and dextrose may
also be used when it is necessary.
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