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?

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