Metric Conversions
1. 300 mg = ____________ g
2. 238 g = _____________ mcg
3. 28 mL = _____________ L
Metric Conversions
1. 300 mg = ____________ g
DRUG CALCULATIONS
When calculating how much of a drug is required, working with the
formula helps the accuracy of the calculation.
Always
DRUG CALCULATIONS
When calculating how much of a drug is required, working with the
formula helps the accuracy of the calculation.
Always remember this formula:
What you want X Quantity it comes in
What you have 1
It’s OK to use a calculator!
1. A patient requires 4 mg of Morphine IVI. Morphine is available as
10mg/ml. How many mls will you draw up?
2. Gentamycin 360 mg is prescribed. Gentamycin is available as
80mg/2ml. How many mls will you draw up?
3. Haloperidol 3 mg IVI is charted. Haloperidol is available as 5mg/ml.
How many mls is required?
4. Frusemide 70mg IVI is charted. Stock dose is 20mg/ml. How many ml
remember this formula:
What you want X Quantity it comes in
What you have 1
It’s OK to use a calculator!
1. A patient requires 4 mg of Morphine IVI. Morphine is a
available as
10mg/ml. How many mls will you draw up?
2. Gentamycin 360 mg is prescribed. Gentamycin is available as
80mg/2ml. How many mls will you draw up?
3. Haloperidol 3 mg IVI is charted. Haloperidol is available as 5mg/ml.
How many mls is required?
4. Frusemide 70mg IVI is charted. Stock dose is 20mg/ml. How many ml
vailable as
10mg/ml. How many mls will you draw up?
2. Gentamycin 360 mg is prescribed. Gentamycin is available as
80mg/2ml. How many mls will you draw up?
3. Haloperidol 3 mg IVI is charted. Haloperidol is available as 5mg/ml.
How many mls is required?
4. Frusemide 70mg IVI is charted. Stock dose is 20mg/ml. How many ml
would you give?
METRIC CONVERSIONS
Metric weights and measurements involve a step-by-step conversion from
one unit to another.
With weight we often convert to smaller (and more numerous units) thus:
Kg gm mg mcg
grams milligrams micrograms
Each of these steps involves the heavier unit being multiplied by 1000 to
bring up the number of the smaller units for the same weight.
kg g 1kg x 1000 = 1000g
g mg 1g x 1000 = 1000mg
mg mcg 1mg x 1000 = 1000mcg
When we multiply by 1000 we move the “decimal point” three places to
the right
0.5g == ?? mg 0.5 x 1000 == 500mg
1 place = 5
2 places = 50
3 places = 500
If we are converting from a lighter unit to a heavier unit we move the
decimal point three places to the left for each conversion. Another way of
putting it is we divide by 1000.
mcg mg 1000mcg 1000 = 1mg
mg gm 1000mg 1000 = 1gm
gm kg 1000gm 1000 = 1kg
500mg = ?? gm 500 1000 = 0.5
Try these:
5. Atropine 0.6 mg = ?mcg
0.6 x 1000 = 600mcg
6. 0.01gm = ? mg
0.01 x 1000 = 10 mg
7. Gentamycin 360mg = ?gm
360 1000 = 0.36gm
8. Digoxin 125mcg = ? mg
125 1000 = 0.125mg
If we are moving across two conversions we repeat the process twice.
For example from grams to micrograms
If we are moving across two conversions we repeat the process twice.
For example from grams to micrograms:
3gm converted to micrograms
Step one:
= 3 x 1000 = 3000mg
Step two:
3000mg x 1000 = 3,000,000mcg
9. Augmentin 1.2gm = ?mcg
1.2 x 1000 = 1200mg
1200 x 1000 = 1,200,000mcg
10. Digoxin 125mcg = ? gm
125 1000 = 0.125mg
0.125 1000 = 0.000125gm
Memory Tip:
“Heavy to light – three places to the right”
Try these:
Convert
11. 1.2 mg to mcg
12. 1.3g to mg
13. 500mcg to mg
14. 0.04 mg to mcg
15. 20mcg to mg
16. 600mcg to g
17. 2g to mcg
When we are converting volumes the process is the same.
Litres ml
1 Litre=-> 1000ml
0.25L--> 250ml
375ml 0.375L
Try these:
Convert
18. 450ml to L
19. 64 ml to L
20. 4.3L to ml
MG/KG DOSE CONVERSION
Often we need to check the dose of a drug or solution that is based
on the patient’s weight.
We multiply the prescribed mg dose by the kg weight of the patient
Prescribed dose - 25mg per kg
Patient’s weight - 66kg
What is the dose required?
25mg x 66kg = 1650mg
= 1.65g
21. Prescribed dose – 50 mg/kg
Patient’s weight – 79 kg
What is the dose required?eq
22. The patient is charted 15mg/kg/day. The patient weighs 75kg.
a) How much is the total dose per 24 hours?
b) How much will the patient receive every 8 hours?
ROUNDING OFF the decimal point
Rounding up if greater than 5, round up eg 166.66 = 167
Rounding down if less than 5, round down eg 33. 33 = 33
INFUSION FLOW RATES
To obtain the hourly rate, divide the volume of fluid to be infused by the
number of hours fluid to be infused over.
Eg: a 1000ml infused over 12 hours
1000
12 = 83.3ml/hr rounded down to 83ml/hr
24. How many ml/hr would a patient receive if they were to have
500ml of fluid infused over 6 hours?
23. A 1L bag is to be infused over 6 hours. Calculate how many mls
per hour the patient will receive.
Fluids are infused using a giving set, requiring a “drop per minute” rate.
The giving sets are:
Standard Metriset = delivers 20 drops per ml.
Micro giving set (Buretrol) = delivers 60 drops per ml.
Always ensure you use the appropriate calibration in your calculations
DROP PER MINUTE Infusion Calculation
A patient is prescribed Sodium Chloride 1000ml
Total fluid in mls x giving set calibration
Total hours x 60 mins 1
DROP PER MINUTE Infusion Calculation
A patient is prescribed Sodium Chloride 1000ml to be infused over
an 8-hour period. A standard giving set is being used.
Calculate the drops per minute.
1000 X 20 = ?drops per minute
8 x 60
25. Your patient is prescribed a 1000ml infusion of Sodium Chloride
0.9% with 40 mmols of Potassium to be given over 6 hours.
Using a buretrol giving set, calculate the drops per minutes he
will receive?