This document provides information and examples for calculating drug dosages and infusion rates. It is divided into 5 sections. Section 1 covers units and equivalences for converting between different dosage units. Section 2 demonstrates calculating the volume needed to administer a given dose. Section 3 shows calculating volume based on drug concentration. Section 4 covers calculating infusion time based on stated infusion rate. Section 5 ties the previous concepts together to calculate appropriate infusion pump rates. Worked examples are provided for various drugs and dosage scenarios.

1. Drug Calculations
September 2018

2. Drug Calculation Assessment
 SECTION 1: Units & Equivalences
 SECTION 2: Calculating dose as volume
 SECTION 3: Drug Strengths & Stated
Concentrations
 SECTION 4: Duration of Infusion – Stated rate
(dose per min) & Infusion rate (mL/hr)
 SECTION 5: Infusion Rate Calculations

3. SECTION 1:
Units & Equivalences
1 Kg = 1,000 g
1 g = 1,000 mg
1 mg = 1,000 micrograms
1 L = 1,000 mL

4. Converting from One Unit to
Another
 To convert from a larger unit to a smaller unit, multiply
by 1000 or move the decimal point three places to the
right
 To convert from a smaller unit to a larger unit, divide
by 1000 or move the decimal point three places to the
left

5. Units & Equivalences
Convert 0.25 mg into micrograms
Convert 600 micrograms to mg

6. Answers
0.25 × 1000 or move decimal point three places to the
RIGHT
= 250 micrograms
600 ÷ 1000 or move the decimal point three places
to the LEFT
= 0.6 mg

7. SECTION 2: Calculating Dose as Volume
What you WANT X what it is IN
What you have GOT
= the volume you want to administer

8. What we
WANT
Furosemide
250mg/10mL
Furosemide Time
0700-0900

1200-1400
Dose
200mg
Route
IV
Start Date
18.05.07
End
Date
1600-1800
2200-2400
Other Time
Signature of
Doctor
P.Rescriber
What we
have GOT
What it is IN
A patient is prescribed 200mg of Furosemide I.V. The
ampoules available contain 250mg in 10mL. What volume
containing the drug do you need to administer?

9. Answer
What you WANT X what it is IN
What you have GOT
200 mg
250 mg × 10 mL
= 8 mL

10. SECTION 3: Drug Strengths & Stated
Concentrations
What you HAVE (mg)
CONCENTRATION (mg/mL)
= How much fluid is required (Volume)

11. Aciclovir Time
0700-0900 
1200-1400 
Dose
250mg
Route
IV
Start Date
18.05.07
End
Date
1600-1800
2200-2400 
Other Time
Signature
of Doctor
Additional
Comments
P.Rescriber
Final
Concentration
5mg/mL
A patient is prescribed 250mg of Aciclovir I.V. Aciclovir has to be
initially reconstituted with water for injection, then added to a bag
of compatible infusion fluid, giving a final concentration of
5mg/mL. How much infusion fluid should be used dilute the
reconstituted Aciclovir to achieve this final concentration?
What we
HAVE
CONCENTRATION

12. Answer
What you HAVE (mg)
CONCENTRATION (mg/mL)
250mg
5mg/mL
= 50 mL

13. A 1% (w/v) solution means that in every 100mL of solution you will
find 1g of drug. Therefore, how many g of Glucose would there be in
500mL of 5% Glucose?
Glucose 5%
500ml

14. Answer
 A 1% (w/v) solution means that in every
100mL of solution you will find 1g of drug.
100mL = 1g
Therefore a 5% w/v must mean that
100mL = 5g
Multiply each side by 5
500mL = 25g

15. 1:10,000 strength means that in every 10,000ml of
solution you will find 1g of Adrenaline. Therefore, how
many mg of Adrenaline would there be in 10mL of
1:10,000 Adrenaline?

16. Answer
 1:10,000 means that 1g of adrenaline is dissolved in
10,000mL.
1g = 10,000mL
1000mg = 10,000mL
Divide both sides by 1000
1mg = 10mL

17. SECTION 4: Duration of Infusion
Stated rate (dose per min)
Infusion rate (mL/hr)
Stated Rate – dose per min
Dose (mg) = Time
Rate (mg/min)

18. Furosemide must be administered at a rate no faster than
4mg/minute. How many minutes would it take to give 200mg
of this drug?
Furosemide Time
0700-0900

1200-1400
Dose
200mg
Route
IV
Start Date
18.05.07
End
Date
1600-1800
2200-2400
Other Time
Signature of
Doctor
Additional
Comments
P.Rescriber
Rate of
4mg/minute
Furosemide
250mg/10mL
Rate
(mg/min)
DOSE
(mg)

19. Answer
Dose (mg) = Time
Rate (mg/min)
200mg
4mg/min
= 50 minutes

20. Infusion rate – mL/hr
Volume (mL) = Rate (mL/min)
Time (Min)
X 60 = Rate (mL/Hr)
* Tip if rate is in hours omit “X 60”

21. Omeprazole
40mg/100mL
Omeprazole (Losec ®) 40mg is diluted in 100mL of
compatible infusion fluid. This infusion has to be given over
20 minutes. What rate should you set the infusion pump at,
in ml/hr, to deliver this dose?

22. Answer
Volume (mL) = Time (mL/hr) x 60
Rate (hr)
100ml
20 mins x 60
= 300mL/hr

23. Acetylcysteine
7.5g/1000mL
Acetylcysteine (Parvolex ®) 7.5g is diluted in 1000mL of
compatible infusion fluid. This infusion has to be given over
16 hours. What rate should you set the infusion pump at, in
ml/hr, to deliver this dose?

24. Answer
Dose (mL) = Time (mL/hr)
Rate (hr)
1000
16
= 62.5 mL/hr

25. SECTION 5: Infusion Rate Calculations
What you WANT x 60 (60 mins per hr)
What you have GOT X what it is IN
= the volume you want to administer

26. Glyceryl Trinitrate Time
0700-
0900
1200-
1400
Dose
25 micrograms/
minute
Route
IV
Start Date
18.05.07
End
Date
1600-
1800
2200-
2400
Other
Time
Signature of Doctor
Additional
Comments
P.Rescriber
Continuous
Infusion
You are required to give a patient Glyceryl Trinitrate as a
continuous I.V infusion at 25 micrograms/minute. You have
prepared a 50mg in 50mL infusion. What rate should you set the
infusion pump at, in ml/hr, to deliver this dose?
What we
WANT Glyceryl
Trinitrate
50mg/50mL
What we
have
GOT
What
its IN
60 mins
per hr

27. Answer
What you WANT x 60 (60 mins per hr)
What you have GOT X what it is IN
25 micrograms x 60 = 1500 micrograms/hr
1500 ÷ 1000
= 1.5 mg
1.5 mg x 50mL
50 mg
= 1.5 mL/hr

28. Any Questions?
Assessment time……