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Dosage
Calculation
•
©2005 by National Healthcare Group. All rights reserved.
Objectives
•Unit of measurement for delivery of intravenous
medicines
•Percent solution
•Common form
ulas used in drug dosage calculation
and flow rate calculation
Units of Measurement
1) International system
of units or metric system
–gram(gm) is the basic unit of weight
–litre(L) is the basic unit for fluid
–mole(m
ole) is the basic unit of substance
Units of Measurement
2) a. International units(IU
)
exam
ple : Insulin expressed in units per m
L
2) b. Milli(m
) is a prefix denoting one thousandth
of a unit
exam
ple : 1 litre
= 1000ml (m
illilitre)
2) c. M
icrogram (mcg/ug) is a prefix denoting
one millionth of a gram
exam
ple: 1gm (gram) = 1000mg (milligram) =
1000 000 (microgram)
3) d. Mega (M
) is a prefix denoting one million unit
exam
ple: 1 M
U is a prefix denoting one million
unit
Units of Measurement
Metric Conversion
•To convert grams to m
illigrams, m
ultiply by 1000
or move the decim
al point 3 places to the right
e.g. 1 g = 1000mcg or
1 0 0 0 .
To convert milligrams to grams, divide by 1000 or
mover the decim
al point 3 places to the left
•1000mcg = 1mg or
1. 0 0 0 = 1mg
•To convert micrograms to m
illigrams, divide by
1000 or move the decim
al point three places to the
left.
e.g 1000mcg = 1mg or 1000/1000 =1 m
g
or 1. 0 0 0
Metric Conversion
Conversion
Convert the following:
a.1.5g = ___ mg
b.25mg = ___ g
c.0.05mg = ___ mcg
d.21000mcg = ___ m
g
Conversion
Convert the following:
a.1.5g = 1500 mg
b.25mg = 0.025 g
c.0.05mg = 50 m
cg
d.21000mcg = 21 mg
Well done !!
Percent solution
•Percent solution is the relationship between the
amount of solute and the total quantity of
solution is expressed percentage or ratio
Percent solution
•Percentage strength of solution m
ay be calculated
in one of the three ways
1. Percent weight/weight (W
/W) is the weight of
the solute (drug) compared to weight of the
solution
-(g drug/100g solution)
Percent solution
2. Percent weight in volume (W
/V) is the weight of
the solute (drug) compared to the volume of the
total solution
-(g drug/100mL solution)
exam
ple : 5% Dextrose m
eans 5gms of
dextrose in 100mL of solution
Example
Calculate the weight of 15% dextrose in
500ml of solution
Dextrose 15% is equivalent to 15g/100ml
If there are 500ml, the am
ount is
15 X 500
= 75g of dextrose in 500ml
100
Percent solution
3. Percent volume in volume (V
/V) is the volume of
the solute compared to the total solution
-(m
Ldrug/100mL solution)
Drug dosage calculation
•Drug dosagecan be calculated using ratio and
proportion or using form
ula. This form
ula is to
calculate amount of medication in solution for oral
IM, IV
and SC to be administered when given a
dosage, stock and volume
exam
ple: Desired dose
x Stock Vol
Stock dose
•Ordered Amoxilsuspension 500 m
g p.o/6
hourly. Supply Amoxil250 m
g in 5 m
l.
How m
uch would you give?
Required dose = 500 m
g
Stock Dose = 250 m
g
Stock Volume = 5 m
l
500mg/250mg X 5ml = 10 m
l
Drug dosage calculation
Calculating drug dosage
If heparin solution is 25000 units/5ml, and Dr
ordered 10000 unit. How m
uch of the solution will
you withdraw?
Use form
ula : desired dose
x vol
stock dose
10000 IU
X 5ml
25000 IU
= 2 m
l of heparin
Calculating drug concentration
Concentration of the drug is the am
ount of the drug
in 1ml of solution.
To calculate the concentration of the drug, use the
form
ula:
dose
volume
Or use proportion
Calculating drug concentration
Exam
ple: if you dilute Rocephine1 gm in 100ml of
norm
al saline 0.9% injection, what is the
concentration?
To calculate by formula
Dosage/Volume
1000mg/100ml
10mg/m
l
To calculate by proportion
e.g.
100ml = 1000mg
1ml = X m
g
Therefore 1ml = 1000mg/100ml = 10mg
1 m
l = 10 m
g
Drug dosage calculation
If you take 25000 unit/5ml of heparin and dilute it in
500ml of norm
al saline 0.9% solution
a.What is the concentration of the solution ?
b.
How do you prepare this solution ?
c.Dr ordered 6000 unit 6 hourly, what is the rate
of infusion per 1 hour ?
Take few m
inutes to Work out the
answ
er
a.What is the concentration ?
25000 units/ 500ml
50 units/ml
b.How to prepare the solution ?
There are 5ml per 25000units
Draw up 5ml of heparin then add to 500ml of
norm
al saline 0.9%
Drug dosage calculation
a.Dr ordered 6000 units 6 hourly, what is the rate
of infusion per 1 hour ?
The concentration (stock) is 50 units per m
l
use form
ula of Desired dose
x Volof solution
stock dose
= 6000unit X 1ml
50unit
= 120 m
l over 6 hours = 120ml/6hours
= 20 m
l / hour
Drug dosage calculation
EXAMPLE 2 :
Constitute dopam
ine 200mg in 150ml of norm
al
saline 0.9% . Patient body weight is 50 kg.
Doctor ordered 2 m
cg/kg/m
in.
a.What is the concentration of the drug?
b.
What is the dosage to be delivered per hour?
c.Calculate the rate of administration for dpomineinfusion
per hour.
Drug dosage calculation
TRY THIS …
…
TAKE 2 M
INS TO CALCULATE
THIS SUM
WELL DONE !!! You have
got it correct
a. Concentration of dopam
ine is calculated using
form
ula : dosage / volume
200mg/150ml = 1.3mg/m
l
b. Dosage to be delivered over an hour is
= 2mcg x 50kg x 60mins
= 6000mcg/hr
= 6mg/hr
c.If the concentration is 1.3mg/m
l, the rate for
delivery is calculated as
desired dose
x volume
stock dose
6mg/hr
X 1 m
l
1.3mg
= 4.6ml / hr
Calculating flow rate
Flow rate calculations require the following
inform
ation :
•Amount of solution to be infused (volume)
•Duration of the administration (time)
•Drop factor of the set to be used
form
ula : Volume
X drop factors
Tim
e in m
inutes
Question:
1 gm of rocephineis diluted in 100ml of norm
al
saline 0.9% . It is to be delivered over 1 hours
through a burette with 20 drops /m
l. Calculate the
flow rate.
100ml X 20drops/ml
60mins
= 33 drops/mins
Calculating flow rate
Go to unit 2 of calculation
module. Attempt all the
questions in this module.