Lecture By Mr.Rami Al-Khateeb King fahd Medical city, Nursing Educator

1. Drug Calculations
Rami AL-Khateeb

2. Outlines
Introduction
Metric Conversions
MG/KG Dose Conversion
Flow Infusion Rates

3. Introduction
When calculating how much of a drug is
required, working with the formula helps the
accuracy of the calculation.

4. Always remember this formula:
What you want X Quantity it comes in
What you have

5. A patient requires 4 mg of Morphine IV.
Morphine is available as 10mg/ml. How many
mls will you draw up?
Please answer questions 1-3

6. 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

7. Metric Conversions
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.

8. Metric Conversions
Kg → g 1kg X 1000 = 1000 gm
g →mg 1g X 1000 = 1000 mg
= 1000 mcg1mg X 1000mg → mcg

9. Metric Conversions
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.

10. Metric Conversions
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

11. Metric Conversions
mcg → mg 1000 mcg /1000 = 1mg
mg →gm 1000mg / 1000 = 1 gm
= 1kg1000gm / 1000gm → kg

12. Please answer questions from 4-7

13. Metric Conversions
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

14. Please answer questions from 8-10

15. When we are converting volumes the process
is the same.
Liters → 1000 ml

16. Please answer questions from 11-13

17. 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

18. MG/KG Dose Conversion
25mg per kg-Prescribed dose
Patient’s weight-66kg
What is the dose required?

19. MG/KG Dose Conversion
25mg x 66kg = 1650mg = 1.65 gm
Please answer questions 14 a & b

20. Flow Infusion Rates

21. Flow Infusion 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 = 83.3 ml / hr

22. Flow Infusion Rates
Please answer questions 15 & 16

23. Flow Infusion Rates
Fluids are infused using a giving set, requiring a “drop per
minute” rate.
The giving sets are:
Standards IV Set = delivers 20 drops per ml.
Micro giving set = delivers 60 drops per ml.
Drop per minutes: total fluid in ml X giving set calibration
total hours X 60 mins

24. Flow Infusion Rates
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 mins
8 X 60

25. Flow Infusion Rates
Please answer question number 17

26. Answers
1. 9 mls
2. 0.6 mls
3. 3.5 mls
4. 600 mcg
5. 10 mg
6. 0.36 gm
7. 0.125 mg
8.1200000 mcg
9. 0.000125 gm
10. 1200 mcg
11. 0.45 L
12. 0.064 L
13. 4300 ml
14.a) 1125 mg
b) 375 mg
15. 167 ml
16. 83 ml
17. 166.6

27. References
Dodds, K.G. (2012). Safety in Numbers–
Essential Calculations for Nurses. Palmerston
North. Dunmore Press Ltd.
Christchurch Hospital Department of Nursing
Drug Calculation Prompt Card
(15/06/00)