PHARMACEUTICAL
CALCULATION &
TECHNIQUES
UNIT 2
Specific learning objectives in this unit:
-
Temperature conversions
Household measurements
Metric system
Apothecary system
Medication abbreviations
Calculating dosages when giving
medications in able or capsule form
Calculating dosages when giving
medications in liquid form
Preparing solutions
Diluting stock solutions
Determining the rate of intravenous
medications
Dosages based on body weight
Dosages based on body surface area
Pediatric dosing
TEMPERATURE
CONVERSIONS
SCALE
FORMULA:
Convert from Celsius to Fahrenheit
∁×
-
CELSIUS AND FAHRENHEIT
-2 common temperature scales used in
pharmacy
𝟓
+ 𝟑𝟐 = 𝑭
Convert from Fahrenheit temp. to
Celsius temp.
𝟓
- (𝑭 − 𝟑𝟐) × = ∁
𝟗
Exampple:
•
-The temperature for storing medication is
extremely important for the stability --- and
therefore the effectiveness ---- of the
medication
𝟗
•
•
•
•
•
•
•
•
•
•
Convert the following
temperatures. Round all your
answers to the tenths position
1)
50º C =
_____º F
2)
47º C =
_____º F
3)
45º C =
_____º F
4)
40º C =
_____º F
5)
37º C =
_____º F
6)
32º C =
_____º F
7)
30º C =
_____º F
8)
25º C =
_____º F
9)
22º C =
_____º F
10)
20º C =
_____º F
•
•
•
•
•
•
•
•
•
•
11)
12)
13)
14)
15)
16)
17)
18)
19)
20)
5º C
2º C
0º C
90º F
89º F
82º F
80º F
79º F
75º F
70º F
=
=
=
=
=
=
=
=
=
=
_____º F
_____º F
_____º F
_____º C
_____º C
_____º C
_____º C
_____º C
_____º C
_____º C
-Specific storage conditions are
required to be printed in product
literature and on drug packaging and
drug labels to ensure proper storage
and product integrity.
2. 5)
An autoclave is usually set to
250°
F
to
sterilize
medical
instruments. What is the equivalent
temperature in degrees Celsius?
The conditions are defined by the following
terms :
•
Cold: any temperature not exceeding
8° C
•
Freezer: -25° to -10° C
•
Refrigerator: 2° to 8° C
•
Cool: 8° to 15° C
•
Room temperature: the temperature
prevailing in a working area
•
Controlled room temperature: 15° to
30° C
•
Warm: 30° to 40° C
•
Excessive heat:
above 40° C
Example 3:
any temperature
Example 2:
1. A prescription is sent to the pharmacy
requesting a substance to be heated
in a 300° F oven for 12-18 hours. At
what Celsius temperature does the
oven need to be set?
Convert the following refrigerator
temperatures and record them in the
appropriate spaces on the log below.
Note any temperatures out of the safe
range (2° to 8° C).
WORKING WITH PESCRIPTIONS
-Prescriptions have been obfuscated by a
combination of Latin and English
abbreviations ( sometimes they even throw in
Greek words)
-Commonly used on prescriptions to
communicate essential information on
formulations, preparation, dosage regimens
and administration of the medication. Our
goal is to demystify this drug nomenclature.
COMMON MEDICAL
ABBREVIATIONS
Categories – for ease of memorization, the
abbreviations have been broken up into
5 CATEGORIES:
1.
2.
3.
4.
5.
Route
Form
Time
Measurement
And other
Meaning
-
Need to place an abbreviation in
context to know its meaning ( e.g., IV
could mean a dosage form as in an “IV
bag”, it could mean a route f
administration as in to “ to give a
medication IV”, or it could even be the
roman numeral meaning “ four”).
LATIN ROOT
-not all the words on this list are derived from
Latin words, nor is it necessary to know the
Latin words to be able to understand the
abbreviations, but it is simply provided to
help you understand how some of these
abbreviations were derived
ABBREVIATIONS
o.s.
o.u.
per neb
p.o.
p.r.
p.v.
SC, SQ
S.L.
-can often be written w/ or w/out the “
periods” and in upper or lower case letters (
e.g., p.o. and PO both mean “ by mouth”)
top
Abbrevia
tion
a.d.
a.s.
a. u.
IM
IV
IVP
IVPB
KVO
n.g.t.
n.p.o.
nare
o.d.
Oculus sinister
Oculus utro
Meaning
Latin root
per os
per rectum
FORM
ROUTE
Abbrevia
tion
Left eye
Each eye
By nebulizer
By mouth
rectally
vaginally
subcutaneousl
y
Sublingually (
under the
tongue)
topically
Meaning
Right ear
Left ear
Each ear
Intramuscular
Intravenous
Intravenous
push
Intravenous
piggyback
Keep vein
open
Naso- gastric
tube
Nothing by
mouth
nostril
Right eye
Latin Rot
Auris dexter
Auris sinister
Auris utro
amp.
aq, aqua
caps
cm.
elix.
liq.
sol.
supp.
SR, XR, XL
syr.
tab.
ung., oint
ampule
water
capsule
Cream
Elixir
Liquid
Solution
Suppository
Slow/extended
release
Syrup
Tablet
ointment
Aqua
capsula
Liquor
Suppositorum
Syrupus
Tabella
ungentum
TIME
Abbrevia
tion
Meaning
Latin Root
a.c.
Before food,
before meals
morning
Around the
clock
Twice a day
Twice a week
hour
Ante cibum
a.m.
atc
Nasquam per
os
Oculus dexter
b.i.d., bid
b.i.w., biw
h, °
Ante meridian
Bis in die
Hora
h.s.
p.c.
p.m.
p.r.n., prn
q.i.d., qid
q
q.d.
q_h, q_°
qod
stat
t.i.d., tid
t.i.w., tiw
At bedtime
After meals
evening
As needed
Four times a
day
Each, every
Every day
Every hour(s)
Every othe
rday
Immediately
Three times a
day
Three times a
week
Hora somni
Post cibum
Post meridian
Pro re nata
Quarter in die
quaque
Quaque die
q.s.ad
statim
Ter in die
MEASUREMENT
Abbrevia
tion
Meaning
i,ii,…
a.a.,aa
ad to,
aq.ad
One,two, etc.
Of each
Up to
Add water up
to
Body surface
area
Cubic
centimeter
dilute
Fluid
Fluid ounce
Gram
BSA
cc
dil
f, fl.
fl.oz
G,g,gm
gtt
I,L
mcg, µg
mEq
mg
ml, mL
q.s.
Latin Root
ana
ad
dilutus
ss
Tbs,T
tsp,t
U
>
<
c
disp
f,ft
n/v
neb
NR
NS
s
Sig
SOB
T.O.
ut dict,
u.d.
V.O,
Drop (s)
Liter
Microgram
milliequivalent
Milligram
Millilitre
A sufficient
quantity
Add sufficient
quantity to
make
One-half
Tablespoon
teaspoon
Unit
Greater than
Less than
with
Dispense
Make, let it be
made
Nausea &
vomiting
Nebulizer
No refill
Normal saline
without
Write/label
Shortness of
breath
Telephone order
As directed
Verbal order
Examples:
MEASUREMENT
Abbrevi
a
tion
Meaning
gr.
Grain
Latin Root
1)
i gtt ou bid x7d
2)
i tab po q6h prn pain
3)
i tab po qid pc
4)
iss tsp po tid prn cough
Guttae
Quantum
sufficiat
Quantum
sufficiat ad
cum
fac, fiat, fiant
sine
Signatura
ut dictum
5)
iii gtt ad q4h x5d
6)
i supp pr q4h prn n/v
7)
i cap po tid ac + hs
8)
i tab sl q5 minutes prn chest pain,
may repeat up to 3 times.
9)
PRESCRIPTION
-
is a written order for compounding,
dispensing and administering drugs to
a specific client or patient and once it
is signed by the physician it becomes a
legal document.
-
Required for all medications that
require the supervision of a physician
must be controlled since they are
addictive and carries the potential of
being abused
-
Could cause health threats from side
effects if taken incorrectly ( e.g.,
cardiac medications, controlled
substances and antibiotics)
ii tabs stat, then i tab po qid x10d
INTERPRETATION
OFPRESCRIPTION AND
MEDICATION ORDER
MEDICATION ORDERS
Learning the Parts of a
Prescription and how to
incorporate Medical
Abbreviations
-
-
“ PRESCRIPTION”
Typical medication order form used in
the hospitals
Forms may be used within a hospital
by specialized units such as infectious
disease, cardiac care, paediatrics,
obstetrics, orthopaedics and others
Drug-specific forms also may be used
as heparin dosing, electrolyte
infusions, and morphine sulphate in
patient-controlled anaesthesia.
-means “ to write before”
- reflects the historical fact that a prescription
traditionally had to be written before a drug
could be mixed and administered to a patient
MILITARY TIME
-
Prae= a prefix meaning before
Scriber= a word root meaning to write
Used not only in the military but
civilian life as well, such as in hospitals,
other patient-care institutions,
emergency services ( e.g., paramedics,
law enforcement )
The following is a list of the parts
of a prescription, and in bold are
the most significant portions:







Patient information
Superscription
Inscription
Subscription
Signatura
Date
Signature lines,
signature, degree,
generic substitution
 Prescriber
information
 DEA# if required
-
Instructions are preceded by the
symbol “S”, or “ Sig”. ( means “ write”
or “ label”
-
Whenever translating the signatura
into instructions for a patient, begin it
with an action verb such as take,
inhale, spray, inject, place, swish, or
whatever other verb seems
appropriate for the medication.
SUPERSCRIPTION
-
consists of the heading where the
symbol Rx ( recipe/ take thou) is found
the Rx symbol comes before the
inscription
INSCRIPTION
-
-
the body of the prescription
Provides the names and quantities of
the chief ingredients of the
prescription
You can find the dose and dosage
form, such as tablet, suspension,
capsule, syrup
SUBSCRIPTION
-
 Refills
 Warnings
SIGNATURA
-
Also called sig, or transcription
Gives instructions to the patient on
how, how much, when and how long
the drug is to be taken.
-
Gives specific directions for the
pharmacist on how to compound the
medication
Directions are usually expressed in
contracted Latin or may consist of a
short sentence such as: “ make a
solution”, “ mix and place into 10
capsules”, or “ dispense 10 tablets”
NOTE : that was in the old days. Today...
doctors just name the pill!
DATE AND PATIENT
INFORMATION
-
Consists of the name of the party for
whom it I designed and the address
Occupies the upper part of the
prescription
E- PRESCRIBING/ EPRESCRIPTION
-
INSTRUCTION
-
●
“ take as directed” = not satisfactory/
should be avoided
The directions to the patient should
include a reminder of the intended
purpose of the medication by including
such phrases as "for pain," "for relief
of headache," or "to relieve itching"
And if the patient is to receive a brand
name medication, rather then generic, the
physician enters NO SUBSTITUTIONS at the
end of the prescription.
●
If there are no refills to be dispensed,
it is advisable not to enter the number 0,
because it can be altered by adding numbers
before the zero, thus making it a 10 to receive
ten refills (or more!).
NOTE : Always write out the word None, or
No Refills!!!
The inpatient or outpatient setting, a
medication order, for a patient is
entered into an automated data entry
system as a personal computer ( PC)
or a handheld device loaded w/ eprescribing software and sent to a
pharmacy
NOTE : Advantages cited foreprescriptions over traditional paper
prescriptions are:
 reduced errors due to prescription
legibility; concurrent software
screens for drug
interactions;
 reduced incidence of altered or forged
prescriptions; efficiency for both
prescriber
and pharmacist;
 convenience to the patient, whose
prescription would likely be ready
for pick-up upon arrival at the
pharmacy
RANGE OF PRESCRIPTION AND
MEDICATION ORDER
CALCULATIONS
DOSES:
TAMPER- RESISTANT Prescription
Pads
-
To prevent the unauthorized copying,
modification or counterfeiting of
prescriptions
-
Including the quantity of a prescribed
dose, the total number of doses
prescribed, and the number of days
the prescribed medication will last
COMPLIANCE :
-
The patient’s or caregiver’s
compliance in meeting the prescribed
direction for dosing
PRESCRIPTIONS AND
MEDICATION ORER ACCURACY
-
DRUG CONCENTRATION:
-
The quantity of an active therapeutic
ingredient to use to achieve the
desired drug concentration
RATE OF DRUG ADMINISTRATION:
-
The quantity of drug administered per
unit of time to meet prescribed dosing
schedule ( e.g., mg/min, drops/
minutes, or mL/hr for the
administration of an intravenous fluid)
CHEMICAL- PHYSICAL FACTORS:
-
Including calculations to make
solutions isotonic, iso-osmotic,
equimolar orbuffered
PHARMACOECONOMICS:
-
Including medications, cost-benefit
analysis, cost-effectiveness analysis,
alternative treatment plans, and
medication pricing
COMPOUNDING:
-
The quantities of active and inactive
components to use in the
extemporaneous preparation of a
pharmaceutical product, including the
use of stock solutions and/ or
prefabricated dosage units in the
process.
It is the responsibility of the
pharmacist to ensure that each
prescription and medication order
received is correct in its form and
content; is appropriate for the patient
being treated; ad is subsequently
filled, labelled and dispensed, and
administered accurately
ERROS AND OMISSIONS
-
To ensure such accuracy , the
pharmacists is obliged to review each
prescription and medication order in a
step- by- step manner to detect erros
of omission
Pharmacist should check for the
correct reading and interpretation of a
prescription or medication order are:
1. prescriber information, including
address and telephone number
2. date of the order and its
currency to the request for
filling;
3. patient information, including
dose-relevant information, such
as the age and/or weight of the
patient if the dose of the drug is
so based;
4. drug prescribed, including dose,
preparation strength, dosage
form, and quantity
5. clarity of any abbreviations,
symbols, and/or units of
measure;
•
. A letter repeated once or more,
repeats its value (e.g., xx 20; xxx 30).
•
2. One or more letters placed after a
letter of greater value increases the
value of the greater letter (e.g., vi
6; xij 12; lx 60).
•
3. A letter placed before a letter of
greater value decreases the value of
the greater letter
6. clarity and completeness of
directions for use by the patient
or caregiver
7. refill and/or generic substitution
authorization
8. need for special labeling, such as
expiration date, conditions for
storage, and foods and/or other
medications not to take
concomitantly
USE OF ROMAN NUMERALS ON
PRESCRIPTION
-
Roman numerals are used commonly
in prescription writing to designate
quantities, as the:
(1) Quantity of medication to be
dispensed and/ or
(2) Quantity of medication to be taken
by the patient per dose
The student also may recall that
the following rules apply in the
use of Roman numerals:
EDICATION SCHEDULING AND
PATIENT COMPLIANCE
MEDICATION SCHEDULING
-
May be defines as the frequency ( i.e.,
times per day) and duration ( i.e..
length of treatment ) of a drug’s
prescribed or recommended use
PATIENT COMPLIANCE
-
w/ prescribed and non-prescribed
medications is defind2 as patient
understanding and adherence to the
director for use.
PATIENT NONCOMPLIANNCE
-
The failure to comply w/ a
practitioner’s or labled direction in the
self
NONCOMPLIANCE
-
underdosage or overdose
-
incorrect duration of treatment
incorrect duration of treatment
drug abuse or misadventuring w/
medications
MATHEMATICAL METHOD / FORMULA
•
Dimensional Analysis or Ratio
Proportion
DO THE MATH
BASIC MEDICATION
CALCULATIONS
𝑟𝑎𝑡𝑖𝑜𝑝𝑟𝑜𝑝𝑜𝑟𝑡𝑖𝑜𝑛
𝑑𝑖𝑚𝑒𝑛𝑠𝑖𝑜𝑛𝑎𝑙𝑎𝑛𝑎𝑙𝑦𝑠𝑖𝑠
50𝑚𝑔 100𝑚𝑔
50𝑚𝑔
𝑚𝐿
×
= 0.5 𝑚𝐿⁄𝑑𝑜𝑠𝑒 𝑁 = 𝑚𝐿
𝑑𝑜𝑠𝑒 100𝑚𝑔
𝑁 = 0.5𝑚𝐿
DOES THE ANSWER MAKE SENSE?
Calculating Dosages When Giving
Medications in Tablet or Capsule Form
STEP METHOD AND DIMENSIONAL
ANALYSIS
•
the quantity of medication per
dose,
•
the strength of the tablet,
•
how often the doses are being
given,
•
how long of a time frame we
need to cover with these doses
Example:
An order for 50 mg of a drug is received. A 10
mL vial with 100 mg/mL is available. How
many mL should be withdrawn from the vial?
QUESTION
•
How many mL should be withdrawn
from the vial?
DATA
•
50mg/dose 10mL/vial 100mg/mL