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Help with Dosage Calculations

I need help with this calculation. I did a cross multiplication, but am not sure that is the way to go with this question.

Calculate the dosage.

A patient with diabetes is receiving an insulin drip of 300 U Regular insulin in 150 mL NS at 10 mL/h. How many U/h of insulin is this patient receiving? U100 insulin: 100 U/mL


This is what i did:

300U/150mL X 10mL/ 1h = 1500/300= 5

TriciaJ, RN

Specializes in Psych, Corrections, Med-Surg, Ambulatory.

Is the insulin already mixed in the saline bag? And the pharmacy label states 300 units per 150 ml? Then I would do the math from there. U100 only matters if you're drawing it up for a subcutaneous injection. Hope this gets you on the right track.

How many units of insulin is there in each ML?

I believe it is. So I would just consider U100 as extra information? So I would determine the units per mL by dividing 150 by 300 and getting 0.5 u/mL. Would I then multiply it by the rate of 10ml/h to get 5 u/h?

If I divide 150u by 300, it would give me 0.5 u/ml I believe.

You've reversed things again. You need to divide the total dose by the volume. Try that and see what you get.

In that case, I would dived 300/150, giving me 2 right?

Boomer MS, RN

Specializes in Med Surg/ICU/Psych/Emergency/CEN/retired.

300 units in 150 ml = 300/150 = ?. The answer will be how many units are in one ml. The concentration is always determined by the amount of the drug (in mcg, mg, or grams or units, for example) divided by the volume of the solution. Then go from there to figure out the answer.

Correct! So if you have 2 units per ml how many units are in 10 mls?

That would give me 20 u/10ml at a rate of 10mL/h. Thank you so Much!!!

Our pleasure.

You are making this very complicated. You need to figure out how much insulin is in 1 mL of NS and go from there. They provided you with information to recognize that answer (or figure it out):

300 U Regular insulin in 150 mL NS

Think of it in everyday terms and I think you will see it is simple, for example :

- Divide $300 evenly amongst 150 people, how many $ would each person have?

Disregard! Glad you got it! :)

Mavrick, BSN, RN

Specializes in 15 years in ICU, 22 years in PACU.

Whatever it's called (dimensional analysis etc) when you do your calculations take the units with the number.

For example: instead of 150/300 write it out 150ml/300units. Then when you actually do the math you will see the result is 0.5ml/unit. NOT units/ml which is what you want to calculate.

Mavrick, BSN, RN

Specializes in 15 years in ICU, 22 years in PACU.

If I divide 150u by 300, it would give me 0.5 u/ml I believe.

Do you see where you got your calculation backwards? You didn't have 150u. "The pharmacy label states 300units per 150ml".

This may be old news. Sounds like you got it already.


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