Sample Problems:
1. A physician prescribes 10 mEq of potassium
chloride for a patient. How many milligrams of
Electrolyte Preparations KCl would provide the prescribed quantity?
● 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.
Electrolyte Solutions
2. A physician prescribes 3 mEq/kg of NaCl to be
● Electrolyte ions in the blood plasma include the administered to a 165-lb patient. How many
cations Na+, K+, Ca2+, and Mg2+ and the anions milliliters of a half–normal saline solution
Cl−, HCO3−, HPO4 2−, SO4 2−, organic acids, (0.45% NaCl) should be administered?
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.
Milliequivalents (mEq)
● is used almost exclusively in the United States
by clinicians, physicians, pharmacists, and
manufacturers to express the concentration of
electrolytes in solution. 3. What is the concentration, in milligrams per
● This unit of measure is related to the total milliliter, of a solution containing 2 mEq of
number of ionic charges in solution, and it takes potassium chloride (KCl) per milliliter?
note of the valence of the ions.
● a unit of measurement of the amount of
chemical activity of an electrolyte.
Formula:
𝑀𝑊
𝑉𝑎𝑙𝑒𝑛𝑐𝑒
1 𝑚𝐸𝑞 = 1000
4. What is the concentration, in grams per
milliliter, of a solution containing 4 mEq of
calcium chloride (CaCl2 · 2H2O) per milliliter?
Millimoles Osmolarity
● A mole is the molecular weight of a substance in ● Osmotic pressure is proportional to the total
grams. number of particles in solution. The unit used to
● A millimole is one-thousandth of a mole and is, measure osmotic concentration is the
therefore, the molecular weight of a substance milliosmole (mOsmol).
in milligrams. ● For dextrose, a nonelectrolyte, 1 mmol (1
formula weight in milligrams) represents 1
Formula:
mOsmol.
𝑀𝑊
1 𝑚𝑚𝑜𝑙 = 1000 Milliosmoles
Sample Problems: Formula:
𝑔
1. How many millimoles of monobasic sodium 𝑊𝑡. 𝑜𝑓 𝑠𝑢𝑏𝑠𝑡𝑎𝑛𝑐𝑒 ( 𝐿 )
𝑚𝑂𝑠𝑚𝑜𝑙 = 𝑀𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝑤𝑒𝑖𝑔ℎ𝑡 (𝑔)
𝑥 𝑁𝑜. 𝑜𝑓 𝑠𝑝𝑒𝑐𝑖𝑒𝑠 𝑥 1000
phosphate monohydrate (m.w. 138) are present
in 100 g of the substance?
Sample Problems:
1. A solution contains 10% of anhydrous dextrose
in water for injection. How many milliosmoles
per liter are represented by this concentration?
Molecular weight of anhydrous dextrose = 180
2. What is the weight, in milligrams, of 5 mmol of
potassium phosphate dibasic (m.w. 174)?
2. Calculate the osmolarity, in milliosmoles per
liter, of a parenteral solution containing 2
mEq/mL of potassium acetate (KC 2H3O2—
m.w. 98).
3. If lactated Ringer’s injection contains 20 mg of
calcium chloride dihydrate (CaCl2 · 2H2O) m.w
147 in each 100 mL, calculate the millimoles of
calcium present in 1 L of lactated Ringer’s
injection. 3. What is the osmolarity of an 8.4% w/v solution
of sodium bicarbonate( m.w. 84)?
Sample Problems:
1. A veterinarian ordered a liter of Hartmann’s
Irrigation (lactated Ringer’s irrigation) with the
following formula: (25 points)
Sodium chloride 600
mg
Sodium lactate 310
mg Osmosis
Potassium chloride 30 ● when a solvent passes through a
mg semi-permeable membrane from a dilute
Calcium chloride, dihydrate 20 solution into a more concentrated one, the
mg concentration becomes equalized.
Water for injection, ad 100 ● The pressure responsible for this phenomenon
mL is termed osmotic pressure and varies with the
nature of the solute.
Calculate the mOsmol/L of Na+ , K+ , Ca2 + , Cl− ● If the solute is non-electrolyte, its solution
, and C3H5O3 −. contains only molecules and the osmotic
pressure varies with the concentration of the
solute. If the solute is an electrolyte, its solution
contains ions and the osmotic pressure varies
with the both the concentration of the solute
and its degree of dissociation.
Isotonic – a solution having the same osmotic pressure
as the specific body fluid.
Hypotonic – solutions of lower osmotic pressure with
the body fluid.
Hypertonic – solutions having higher osmotic pressure
2. How many (a) millimoles, (b) milliequivalents,
with the body fluid.
and (c) milliosmoles of calcium gluconate
(Ca(C6H11O7 )2— m.w. 430) are represented in
15 mL of a 10% w/v calcium gluconate solution?
Example: Calculation of the Factor
1. Ferrous Sulfate is a 2 ion electrolyte,
dissociating 60% in a certain concentration.
Calculate its dissociation (i) factor.
2. Sodium Carbonate dissociates in a certain 2. Morphine sulfate (mw=759) is a 3-ion
concentration at 70%. Calculate its dissociation electrolyte, dissociating 60% in a concentration.
(i) factor. Calculate the sodium chloride equivalent.
● Most medicinal salts approximate the Procedure in the calculation of isotonic solutions with
dissociation of sodium chloride in weak NaCl equivalents:
solutions. If the number of ions is known, we
may use the following values: 1. Calculate the amount in grams of sodium
Non-electrolytes and subs of slight dissociation: chloride represented by the ingredients in the
1.0 Subs. that dissociate in to 2 ions: 1.8 prescription. Multiply the amount in grams of
3 ions: 2.6 each substance by its sodium chloride
4 ions: 3.4 equivalent.
5 ions: 4.2
2. Calculate the amount in grams of sodium
Calculations of the NaCl equivalent: chloride alone, that would be contained in an
isotonic solution of the volume specified in the
Formula: prescription, namely, the amount of sodium
𝑀𝑊 𝑜𝑓 𝑁𝑎𝐶𝑙
×
𝑖 𝑓𝑎𝑐𝑡𝑜𝑟 𝑜𝑓 𝑆𝑢𝑏𝑠
= 𝑁𝑎𝐶𝑙 𝑒𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡 chloride in a 0.9% solution of the specified
𝑖 𝑓𝑎𝑐𝑡𝑜𝑟 𝑜𝑓 𝑁𝑎𝐶𝑙 𝑀𝑊 𝑜𝑓 𝑆𝑢𝑏𝑠
volume.
Examples:
3. Subtract the amount of sodium chloride
1. Ephedrine hydrochloride (mw= 202) is a 2-ion represented by the ingredients in the
electrolyte, dissociating 75% in a given prescription (Step 1) from the amount of
concentration. Calculate the sodium chloride sodium chloride, alone, that would be
content. represented in the specific volume of an
isotonic solution (Step 2). The answer
represents the amount (in grams) of sodium
chloride to be added to make the isotonic
solution.
4. If an agent other than sodium chloride, such as
boric acid, dextrose or potassium nitrate is to be
used to make a solution isotonic, divide the
amount of sodium chloride (Step 3) by the
sodium chloride equivalent of the other
substance.
Example Calculations of tonicic agent required: Using an isotonic Sodium chloride to prepare other
isotonic solutions:
1. Rx Cocaine hydrochloride 0.6
Eucatropine hydrochloride 0.6 A 0.9% w/v sodium chloride solution may be used to
Chlorobutanol 0.1 compound isotonic solutions of other substances as
Sodium chloride q.s. follows:
Purified water ad 30
Make isoton. Sol.
Sig. For the eye. Step 1: Calculate the quantity of the drug substance
needed to fill the prescription or medication order.
How many grams of sodium chloride should be
used in compounding the prescription?
Step 2: Use the following equation to calculate the
volume of water needed to render a solution of the
drug substance isotonic.
'
𝑔 𝑜𝑓 𝑑𝑟𝑢𝑔 ×𝑑𝑟𝑢𝑔 𝑠 𝐸 𝑣𝑎𝑙𝑢𝑒
0.0009
= 𝑚𝐿 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑛𝑒𝑒𝑑𝑒𝑑 𝑡𝑜 𝑚𝑎𝑘𝑒
Step 3: Calculate the volume 0.9% w/v sodium chloride
solution to complete the required volume of the
prescription or medication order.
Example:
2. Rx Tetracaine hydrochloride 0.1 1. Rx Phenylephrine hydrochloride
Zinc sulfate 0.05 1%
Boric acid q.s. Chlorobutanol
Purified water ad 30 0.5%
Make isoton. Sol. Sodium chloride
Sig. Drop in eye q.s.
Purified water ad
How many grams of boric acid should be used in 15
compounding the prescription? Make isoton. Sol.
Sig: Use as directed
How many mL of a 0.9% solution of sodium
chloride should be used in compounding the
prescription?
Freezing Point Data in Isotonicity Calculations
Freezing point data (∆Tƒ)
How is HLB Values computed?
● can be used in isotonicity calculations when the
agent has a tonicic effect and does not ● The systematic choice of emulsifying agents in
penetrate the biologic membranes in question. the formulation of many emulsion systems
The freezing point of both blood and lacrimal depends on their HLB
fluid is -0.52°C. A pharmaceutical solution that (hydrophile-Lipophile-Balance) values. These
has a freezing pt same with the blood is said to values form the basis of the so-called HLB
be isotonic. system, which was developed by Griffin.
The system presupposes a scale of HLB numbers and is
1. How many milligrams of Naphazoline based on the facts…
hydrochloride and sodium chloride are needed
to produce 75 mL of 1% isotonic solution with 1. that every surfactant or emulsifier molecule in
lacrimal fluid? part hydrophilic and in part lipophilic
2. that a certain balance between these two parts
is necessary for various types of surfactant
functions. In this scheme, each surfactant or
emulsifying agent is assigned a number that
varies from 1 to 20.
● The lower values are assigned to substances
2. How many mg of Atropine sulfate and boric acid that are predominantly lipophilic (oil loving) and
are required to prepare 15 mL of 1% of atropine have a tendency to form water-in-oil (w/o)
sulfate isotonic with tears? emulsions.
● The higher values are given to those materials
that show hydrophilic (water-loving)
characteristics and favor the formation of
oil-in-water (o/w) emulsions.
● Consequently, the HLB number of an
emulsifying agent is an index of the type of
3. How many milligrams of dextrose and sodium emulsion that has the greatest tendency to
chloride are needed to produce 1L of 1% form.
dextrose isotonic with blood? ● When two or more emulsifiers are combined,
the HLB of the combination is determined
arithmetically by adding the contribution that
each makes to the HLB total of the mixture.
and development to the costs of drug therapy
analyzed against therapeutic outcomes.
Drug therapy and other means of treatment are
intended to serve the healthcare interests the patient
while being cost-effective. In prescribing drug therapy,
clinical as well as economic factors are important
considerations in the selection of the drug substance
and drug product.
SAMPLE PROBLEM
1. What is the HLB of a mixture of 40% of Span 60 For example, if an expensive drug reduces morbidity
and 60% of Tween 60? and hospitalization time, it is considered both
therapeutically advantageous and cost effective. If,
however, a less expensive drug would provide
therapeutic benefit comparable to the more expensive
drug, the less costly drug is likely to be selected for use.
Cost differential between drugs
Example:
An antihypertensive drug is available from
various manufacturers at prices per 100 tablets ranging
from P6.26 to P25.50, with a mean price of P10.75. If a
patient presents a prescription for a 6-month supply of
2. In what proportion should Tween 80 and Span the drug calling for two tablets daily, calculate the
80 be blended to obtain a required HLB of 12? differentials in the cost of the drug to the pharmacy
between the highest, mean and lowest cost products.
Pharmacoeconomics
● encompasses the economic aspects of drug,
Discounts
from the costs associated with drug discovery
● Provided by suppliers may be based on quantity
buying and/or payment of invoices within a
2. The cost of 100 antacid tablets is $2.10. What
specified time period. In addition, for
should be the selling price per 100 tablets to
nonprescription products, discounts may be
yield a 40% gross profit on the selling price?
available for certain seasonal or other
promotional products, bonuses in terms of free
merchandise, and advertising and display
allowances. These discounts provide the
pharmacy with a means of increasing the gross
profit on selected merchandise.
Net cost given list price and allowable discount
What are the Common Methods of Prescription
Example: Pricing?
1. The list price of an antihistamine elixir is P6.50 1. Percent Mark up. In this common method, the
per pint, less 40%. What is the nest cost per pint desired percent markup is taken of the cost of
of elixir? the ingredients and added to the cost of the
ingredients to obtain the prescription price.
Formula:
𝑃𝑟𝑒𝑠𝑐𝑟𝑖𝑝𝑡𝑖𝑜𝑛 𝑃𝑟𝑖𝑐𝑒 =
𝐶𝑜𝑠𝑡 𝑜𝑓 𝑖𝑛𝑔𝑟𝑒𝑑𝑖𝑒𝑛𝑡𝑠 + (𝑐𝑜𝑠𝑡 𝑜𝑓 𝑖𝑛𝑔𝑟𝑒𝑑𝑖𝑒𝑛𝑡 ×% 𝑚𝑎𝑟𝑘𝑢𝑝
Example:
If the cost of the quantity of a drug
product to be dispensed is P4.00 and the
pharmacist applies an 80% markup on cost,
what would be the prescription price?
Markup
● used interchangeably with the term margin of
profit (gross profit), refers to the difference 2. Percent Markup plus a minimum professional
between the cost of merchandise and its selling fee. In this method, both a percent markup and
price. a minimum professional fee are added to the
● Calculating the selling price of merchandise to cost of the ingredient.
yield a given percent of gross profit on the cost Formula:
involves the following. 𝑃𝑟𝑒𝑠𝑐𝑟𝑖𝑝𝑡𝑖𝑜𝑛 𝑃𝑟𝑖𝑐𝑒 =
Example: 𝑐𝑜𝑠𝑡 𝑜𝑓 𝑖𝑛𝑔𝑟𝑒𝑑𝑖𝑒𝑛𝑡 ×% 𝑚𝑎𝑟𝑘𝑢𝑝) + 𝑚𝑖𝑛𝑖𝑚𝑢𝑚 𝑝𝑟𝑜𝑓𝑒𝑠𝑠𝑖𝑜𝑛𝑎𝑙 𝑓𝑒𝑒
1. The cost of 100 antacid tablets is P2.10. What
would be the selling price per tablet to yield a Example: If the cost of a drug product to be
66 2/3% gross profit on cost? dispensed in P4.00 and pharmacist applies a
40% markup on cost plus a professional fee of
P2.25, what would be the prescription price?
3. Professional Fee. This method involves addition
of a specified professional fee to the cost of
ingredients used in filling a prescription.
Formula:
𝐶𝑜𝑠𝑡 𝑜𝑓 𝑡ℎ𝑒 𝑖𝑛𝑔𝑟𝑒𝑑𝑖𝑒𝑛𝑡𝑠 + 𝑝𝑟𝑜𝑓𝑒𝑠𝑠𝑖𝑜𝑛𝑎𝑙 𝑓𝑒𝑒 = 𝑝𝑟𝑒𝑠𝑐𝑟𝑖𝑝𝑡𝑖𝑜𝑛
Example: If the cost of the quantity of a drug
product to be dispensed is P4.00 and the
pharmacist applies a professional fee of P4.25,
what would be the prescription price?
