microsoft powerpoint - drug calculation (1)

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.