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Math for the Pharmacy Technician:
Concepts and Calculations
Egler • Booth
Chapter 7: Oral Medications
and Parenteral Dosages
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Oral Medications and Parenteral
Dosages
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Learning Objectives
When you have successfully completed Chapter 7, you will
have mastered skills to be able to:
 Distinguish between different types of
oral medications.
 Recognize the types of solid oral
medications that may not be altered by
crushing or opening them.
 Calculate the amount of a parenteral
medication to administer.
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Learning Objectives
(con’t)
 Select the appropriate syringe.
 Correctly reconstitute powdered
medications.
 Calculate the amount of reconstituted
medications to administer.
 Accurately calculate doses of inhalant,
rectal, and transdermal medications.
 Identify errors that occur in calculating and
preparing parenteral doses.
 Calculate estimated days supply.
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Introduction
 You will learn to apply the simple
calculation methods learned in Chapter 6
to oral dosages, including solids and
liquids.
 Follow the method of calculation that you
have chosen by following the color coded
examples.
Remember that excellence is a must
with dosage calculations.
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Tablets and Capsules
Solid oral medications
come in several
forms:
•
•
Tablets
Capsules
•
Caplets
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Tablets
Most common form of solid oral
medications
 Combines with inactive ingredients
 Forms a solid disk or cylinder





to be swallowed
sublingual
buccal
chewable
dissolve in water
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Caplets
 Oval-shaped
 Special coating -- easier to swallow
Caplet
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Capsules
 Oval-shaped gelatin shells
 Contain medication in powder or


granule form
The shell is usually two pieces that
fit together
The shell can be separated to
remove the medication when the
patient cannot swallow a pill
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Gelcaps
 Usually a liquid medication in a
gelatin shell
 Not designed to be opened
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Scored Tablets




Scoring allows the
tablet to be divided
when smaller doses
are ordered
Most often, scored
tablets divide into
halves
Some divide into thirds
or quarters
Medication is evenly
distributed throughout
the tablet
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Calculating Dosages for
Tablets and Capsules
 Always question and/or verify when
your calculation indicates to give a
portion of a tablet when the tablet is
not scored.
 Question and recheck any
calculation that indicates that you
should dispense more than three
tablets or capsules.
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Calculating Dosages for
Tablets and Capsules (con’t)
Follow these steps when determining the
amount of medication to be dispensed to a
patient:
1. If necessary, convert the dosage
ordered (O) to the desired dose (D)
that has the same unit of measurement
as the dose on hand (H).
2. Calculate the amount to dispense by the
method of your choice.
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Calculating Dosages for
Tablets and Capsules (con’t)
Follow these steps when determining the
amount of medication to be dispensed to a
patient:
3. Apply critical thinking skills to determine
whether the amount you have calculated
is reasonable.
Recheck your calculation if necessary.
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Review and Practice
The order is to give the patient 15 mg
codeine PO now.
You have 30 mg tablets available.
Calculate the correct amount of medication
to give using one of the following
methods.




Fraction Proportion
Ratio Proportion
Dimensional Analysis
Formula Method
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Fraction Proportion Method
Calculating the Amount to Dispense by Fraction
Proportion:
1. Set up the proportion as follows:
dosage unit
amount to dispense
dose on hand
desired dose
2. Cancel units.
3. Cross multiply, then solve for the unknown value.
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Ratio Proportion Method
Calculating the Amount to Dispense by Ratio Proportion:
1. The proportion will be set up as follows:
dosage unit : dose on hand :: amount to dispense : desired
dose
Or
Q : H :: A : D
2. Cancel units.
3. Multiply the means and extremes then solve for the missing
value.
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Dimensional Analysis
Method
Calculating the Amount to Dispense by Dimensional
Analysis:
With dimensional analysis you will not need to calculate the
desired dose and amount to dispense separately.
You will place your unknown (amount to dispense) on one side
of the equation then multiply a series of factors on the right
side of the equation.
Canceling units will help you determine the equation has been
set up correctly.
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Dimensional Analysis Method
(con’t)
Calculating the Amount to Dispense by Dimensional
Analysis (con’t):
1. Determine the units of measure for the answer and place it
as the unknown on one side of the equation.
2. On the right side of the equation, write a conversion factor
with the units of measurement for the desired dose on top
and the unit of measurement for the dose on hand.
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Dimensional Analysis
Method (con’t)
Calculating the Amount to Dispense by Dimensional
Analysis (con’t):
3. Multiply the conversion factor by a second factor: the
dosage unit over the dose on hand.
4. Multiply by a third factor: dose ordered over the number
one.
5. Cancel units on the right side of the equation. The
remaining unit of measure on the right side of the equation
should match the unknown unit of measure on the left side
of the equation.
6. Solve the equation.
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Formula Method
Calculating Amount to Dispense Using the Formula
Method:
1. Determine the desired dose. Determine the dose on hand
(H) and dosage unit (Q)
D xQ A
H
2. Fill the formula
•D for the desired dose
•H for the dose on hand
•Q for the dosage unit in the formula
•A for the unknown or the amount to dispense
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Formula Method (con’t)
Calculating Amount to Dispense Using the
Formula Method (con’t):
3. Cancel the units.
4. Solve for the unknown.
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Review and Practice
The order is to give the patient 15 mg
codeine PO now.
You have 30 mg tablets available.
Calculate the correct amount of medication
to give using one of the following
methods.




Fraction Proportion
Ratio Proportion
Dimensional Analysis
Formula Method
Answer: ½ tablet
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Crushing Tablets or Opening
Capsules
Uses:
• Patients who have difficulty
swallowing pills
• Patients who have tube feedings
 nasogastric tubes
 gastrostomy tubes
 jejunostomy tubes
May need physician order first
 Check the policy
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Crushing Tablets or Opening
Capsules (con’t)
Mixing
•
•
•
•
Crush certain tablets.
Open certain capsules.
Mix with soft foods or liquids.
Check for interactions between
medication and the food or fluid.
 Example - Tetracycline is inactivated by
milk and should not be given with
antacids or vitamin and mineral
supplements.
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Crushing Tablets or Opening
Capsules (con’t)
Tube feedings
• Must first dissolve the crushed
tablet or opened capsule in a
small amount of warm water.
 If medication cannot be crushed, see
if an alternative form of the
medication exists and ask the
physician to order it that way.
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Some Common Food and
Drug Interactions
Medication:
Mixed with:
Causes:
Antipsychotics
Coffee and tea
Reduces
effectiveness
of drug
Bronchodilators
Caffeine
Stimulates
the CNS
Central Nervous
System (CNS)
Depressants
Black cohosh,
ginseng, kava kava,
St. John’s wort,
valerian, ETOH
Intensifies
sedative
effects of CNS
depressant
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Some Common Food and
Drug Interactions (con’t)
Medication:
Mixed with:
Causes:
Erythromycin
Acidic fruits or
juices,
carbonated
beverages
Decreases
antimicrobial
activity
Ferrous
sulfate
Tea
Decreased
absorption
Haloperidol
Coffee and tea
Decreased
absorption
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Some Common Food and Drug
Interactions (con’t)
Medication:
Insulin
Monoamine
oxidase
inhibitors
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Mixed with:
Coffee
Causes:
Stimulated
excretion
Foods containing Headache,
tyramine such
nosebleed,
as hard cheeses, chest pain,
chocolate, red
severe
wine, and beef
hypertension
or chicken liver
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Some Common Food and Drug
Interactions (con’t)
Medication:
Mixed with:
Causes:
Tetracyclines
Dairy products
Reduces
effectiveness
of drug
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Crushing Tablets or Opening
Capsules
To prevent an incorrect dose of
medication, do not crush or
otherwise alter any of the following:
 Enteric-coated tablets
 Sustained-release forms of medication
 Any tablet with a hard shell or coating
 Tablets for sublingual or buccal use
 Capsules with seals that prevent
separating the two parts
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Enteric-coated Tablets
 Have a coating that
dissolves only in an alkaline
environment such as the
small intestine
 Deliver medication that
would be destroyed by the
stomach acid or that could
injure the stomach lining
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Enteric-coated Tablets
(con’t)
 Often look like candies that have a
soft center and a hard shell
 Must never be crushed, broken, or
chewed
 Must be swallowed with their
coating intact
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Sustained-Release
Medications
 Allows the drug to be released
slowly into the bloodstream over a
period of several hours.
 If the medication is scored, it may
be broken at the scored line.
 Do not crush or dissolve.
 This would allow too much medication
to be absorbed at one time.
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Spansules
 These contain granules of

medication with different
coatings that delay release
of some of the medication.
You may open spansules
and gently mix the granules
in soft food, but do not
crush or dissolve the
granules.
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Medications That Must Not Be
Crushed or Dissolved
 Names that indicate sustainedrelease medications:
-Bid
-Dur
Plateau Cap
Span
SA
SR
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LA
CR
XL
Sequel
Spansule
Extentab
Tempule
Chronotab
Repetab
Tembid
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Medications That Must Not
Be Crushed or Dissolved (con’t)
 Names that indicate enteric-coated
medications:
EC
Enseal
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Reconstituting Liquid
Medications
Reconstituting Liquid Medications:
 Use only the liquid specified on the
drug label.
 Use the exact amount of liquid specified
on the drug label.
 Check the label to determine whether
the medication should be shaken before
dispensing.
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Reconstituting Liquid
Medications (con’t)
Reconstituting Liquid Medications:
 Check the label to determine whether the
reconstituted medication must be
refrigerated.
 Write on the label



The date and time you reconstituted the
medication.
Your initials.
Strength of reconstitution.
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Reconstituting Liquid
Medications (con’t)
Reconstituting Liquid Medications:
 Check the label to determine how
long the reconstituted medication
may be stored.
 Discard any medication left after this
time period has passed.
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Reconstituting Liquid
Medications (con’t)
Reconstituting Liquid Medications:
 When medication can be
reconstituted in different strengths,
select the strength that will allow
the desired dose in the smallest
volume.
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Reconstituting Liquid
Medications (con’t)
Reconstituting Liquid Medications:
 Read the order carefully when calculating
the amount to dispense.
 The physician usually orders the dose in
units of drug, not volume of liquid.
 Calculate the volume needed to dispense
the desired dose.
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Calculating the Volume of
Liquid Oral Medication
To calculate the volume of liquid oral
medication to Dispense, use the same
methods that you use for solid oral
medications:
fraction proportions
•ratio proportions
Q Q
A

•formula
H
•dimensional analysis
•
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Calculating the Volume of
Liquid Oral Medication (con’t)
Find the amount to Dispense.
 Ordered: Ventolin 5 mg PO now
 On hand: Ventolin syrup 2 mg per 5 mL
Use the calculation method of choice.
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Fraction Proportion Method
Calculating the Amount to Dispense by Fraction
Proportion:
1. Set up the proportion as follows:
dosage unit
amount to Dispense
dose on hand
desired dose
2. Cancel units.
3. Cross multiply, then solve for the unknown value.
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Ratio Proportion Method
Calculating the Amount to Dispense by Ratio
Proportion:
1. The proportion will be set up as follows:
dosage unit : dose on hand :: amount to Dispense : desired
dose
Or
Q : H :: A : D
2. Cancel units.
3. Multiply the means and extremes then solve for the missing
value.
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Dimensional Analysis Method
Calculating the Amount to Dispense by Dimensional
Analysis:
With dimensional analysis you will not need to calculate the
desired dose and amount to dispense separately.
You will place your unknown (amount to dispense) on one side
of the equation then multiply a series of factors on the right
side of the equation.
Canceling units will help you determine the equation has been
set up correctly.
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Dimensional Analysis
Method
Calculating the Amount to Dispense by Dimensional
Analysis (con’t):
1. Determine the units of measure for the answer and place it
as the unknown on one side of the equation.
2. On the right side of the equation, write a conversion factor
with the units of measurement for the desired dose on top
and the unit of measurement for the dose on hand.
3. Multiply the conversion factor by a second factor: the
dosage unit over the dose on hand.
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Dimensional Analysis
Method
Calculating the Amount to Dispense by Dimensional
Analysis (con’t):
4. Multiply by a third factor: dose ordered over the number
one.
5. Cancel units on the right side of the equation. The remaining
unit of measure on the right side of the equation should
match the unknown unit of measure on the left side of the
equation.
6. Solve the equation.
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Formula Method
Calculating Amount to Dispense Using the
Formula Method:
1. Determine the desired dose. Determine the dose on hand (H)
and dosage unit (Q)
D xQ A
H
2. Fill the formula
•D for the desired dose
•H for the dose on hand
•Q for the dosage unit in the formula
•A for the unknown or the amount to dispense
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Formula Method (con’t)
Calculating Amount to Dispense Using the
Formula Method (con’t):
3. Cancel the units.
4. Solve for the unknown.
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Patient Education:
Liquid Medications
 Read the label to learn how to store
the medication.
 Use the measuring device provided
or a device purchased specifically to
measure medications.
 Household teaspoons and tablespoons
do not measure liquid accurately.
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Patient Education:
Liquid Medications
(con’t)
 Do not store medication longer than
the label indicates.
 Medication used after expiration date
may have lost potency or its chemical
composition may have changed.
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Patient Education:
Liquid Medications
(con’t)
 Wash the measuring device with hot water
and a dishwashing detergent after each
use.


Dry it thoroughly.
Store it in a clean container such as a plastic
sandwich bag.
 Keep liquid medication in its original
container.

Do not transfer it to other containers.
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Parenteral Dosages
 Parenteral route of administration; medications
that are delivered outside of the digestive
tract; most often refers to injections. The most
common injection types used to deliver
medications include:
 Intramuscular (IM)-Medication administered into
a muscle by injection.
 Subcutaneous (Sub-Q)-Medication administered
under the skin by injection.
 Intravenous (IV)-Medication delivered directly to
the bloodstream through a vein.
 Intradermal (ID)-Medication administered
between the layers of skin.
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Parenteral Dosages
(cont.)
 Injections are mixtures that contain the drug
dissolved in an appropriate liquid.
 The dosage or solution strength on an injectable
medication’s label indicates the amount of drug
contained within a volume of solution.
 Dosage strength may be expressed in milligrams per
milliliter, as a percent, or as a ratio.
 Once you have determined the amount to be
administered to the patient, you must select the
appropriate syringe.
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Parenteral Dosages
(con’t)
 Selecting a syringe
1. If the amount of injection to administer is 1 mL
or more, use a standard 3-mL syringe.
2. If the amount of injection to administer is less
than 1 mL but greater than or equal to 0.5 mL,
use a 1-mL tuberculin syringe.
3. If the amount of injection to administer is less
than 0.5 mL, use a 0.5-mL tuberculin syringe.
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Other Medication Routes
 Medications may be given by a
variety of routes besides oral and
common parenteral routes. These
routes are used for:




inhalants
ophthalmic and otic drops
topical and transdermal
rectal and vaginal medications.
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Other Medication Routes
(con’t)
 Inhalant-medication administered
directly to the lungs, usually through
a metered-dose inhaler or nebulizer.
 Topical-medications are applied to
the skin and include ointments,
creams, and lotions.
 Transdermal-medications are
administered through the skin,
typically via a patch.
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Other Medication Routes
(con’t)
 Ophthalmic medications are used for
the eyes and
 Otic medications are used for ears.
 Both are usually given in liquid/drop
form.
 Some ophthalmic medications are
supplied in ointment form.
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Other Medication Routes
(con’t)
 Rectal-medication administered
through the rectum, usually a
suppository.
 Vaginal-medication administered
through the vagina, in suppository,
cream or tablet form.
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Estimated Days Supply
 As a pharmacy technician you may need
to determine the estimated days
supply of a prescription, which is how
long the medication will last the patient if
taken correctly.
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Estimated Days Supply (cont.)
 To determine estimated days supply you
will multiply amount of medication to
dispense by days needed over the
number of dosage units per day.
Amount to dispense 
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? days
= estimated days supply
dosage units per day
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Review and Practice
True or False
Any tablet can be broken in half
to give to a patient.
Answer: False
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Review and Practice
True or False
Enteric-coated tablets can be
crushed to give to a patient.
Answer: False
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Review and Practice
 Which of the following foods are
contraindicated to mix with
tetracyclines?
A. Water
B. Orange juice
C. Milk
D. Applesauce
Answer: C. Milk
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Review and Practice
 Which of the following types of
medications can be crushed for
administration?
A. Scored tablets
B. Enteric-coated tablets
C. Sustained-release tablets
D. Sublingual tablets
Answer: A. Scored tablets
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Review and Practice
 What preparation must be done
before Dispensing medication
through a nasogastric tube?
A.
B.
C.
D.
Nothing special is needed.
Mix the medication with applesauce.
Mix the medication with warm water.
Mix the medication with ice cream.
Answer: C. Mix with warm water.
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Oral Medications and Parenteral
Dosages
Remember that excellence is a must
with dosage calculations.
THE END
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