Intravenous infusion is a calculation which ensures that the total medicine needed by the patient is given at the required rate.

So they are a few things we need to know:

• The total dose of medicine required by the patient?
• How much of the drug we need to add to the IV infusion bag?
• Is there is a maximum infusion rate the medicine can be given?
• What is the rate? That is to say, how many mLs per minute needs to be administered to the patient

Example 1

Drug Y is required by the patient at a rate of 1200mcg/Kg with the patient weighing 60kg.

250mg of Drug Y is reconstituted in 5mL then made up to a 250mL 0.9% sodium chloride infusion bag.

How many mLs of Drug Y infusion bag solution is required to treat this patient? Drug Y is given at a maximum infusion rate of 40mg/hour.  How many minutes will this be administered over?

Lets break this question down with the following:

Step 1: What is the total dose of Drug Y needed by the patient?

1200mcg/kg is the required dose. Which is the same as 1.2mg/kg.

The patient weighs 60 kg.

So, 1.2mg x 60 = 72mg

The total dose required by the patient will be 72mg of Drug Y

Step 2: What is the concentration of Drug Y in the infusion bag?

250mg of Drug Y is reconstituted in 5mL then made up to 250mL of 0.9% sodium chloride infusion bag.

So this will be 250mg in 250mL of 0.9% sodium chloride.

Note the 0.9% strength of sodium chloride is irrelevant here.

The infusion bag will therefore contain: 250mg/250ml which is the same as 1mg/1ml

Step 3: How many mLs of Drug Y solution is required to treat this patient?

As in step 1 the total dose required for the patient is 72mg and the infusion bag contains 1mg/1mL of Drug Z.

Therefore how many mLs of the infusion bag would we need to give the patient if the dose of Drug Z is 72mg ?

72mL of the infusion bag will contain 72 mg of drug Z.

The patient requires 72mLs of Drug Z solution

Step 4: How many minutes will this be administered over?

Drug Y maximum infusion rate is 40mg/hour same as 40mg/60mins.

We need to give 72mg to the patient.

40mg/60minutes can be simplified down to 10mg/15 mins

10mg/5mins X 70 =  70mg/105mins

10mg/15mins can be simplified down to 1mg/1.5minutes

so 2mg would be 2mg/3minutes

70mg/105min + 2mg/3mins = 72mg/108mins

Therefore the total time of Drug Y administration would be 108 minutes

If you need further help please post a comment below. You can also post any IV question you maybe struggling with.

Yasin Bhaiji

Managing Director

PreRegPharm.co.uk