Medicine Reconstitution, HELP!

Nursing Students General Students

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I am having a problem calculating reconstitution math problems. Here are two math problems that seem easy, I just do not understand the problems?

1. A vial of cefazolin contains 1.2 mL of powder. The total volume of the vial when the powder is reconstituted is 10 mL. What is the amount of sterile water needed to reconstitute the powder?

2. Cefazolin is supplied in 1 gram vials of powder which is reconstituted with 2.5 mL of NaCl for injection for a final volume of 3 mL. What is the approximate concentration of Cefazolin in each milliliter?

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Both of these problems use very basic math, but like most word problems you need to filter out the information you don't need. Some people go omg I need to know everything about this drug when in reality it is asking how many tablets you need to give. Just because it is involved in medication administration doesn't mean it comes into play on the math side of things. The first step is finding what the question is actually asking for. Look at the stuff directly in front of the question mark. What kind of units will your answer use based on the question? Examples include volume(2 L, 6 tsp), quantity(1 tablet), mass(mg, kg) ratio(g/kg) etc. If you don't know what the units could possibly be look at the numbers and units you have to go off of and it should give you an inkling.

I hope this helps if you are still confused please tell me which parts exactly are holding you up.

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Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.

Welcome to AN! We are Happy to help but we will not do it for you.what do you have so far?

DosageHelp.com - Helping Nursing Students Learn Dosage Calculations

If you have 1.2ml of powder how many cc's would you add to get 10 cc's?

If you have 1gram of drug in a total of 3 cc's........ how many mg's are there in each cc?

Before doing the calculation, convert units of measurement to one system.

  1. Basic Formula: Frequently used to calculate drug dosages.
    D (Desired dose) H (Dose on hand) Q (Quantity -tablet or liquid)
    [TABLE]
    [TR]
    D
    Hx Q = Amount to Give[/TR]
    [/TABLE]

    D = dose ordered or desired dose H = dose on container label or dose on hand Q = form and amount in which drug comes (tablet, capsule, liquid)

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1. I subtracted 1.2ml from 10ml. Leaving 8.8ml of water. Is this right?

2. I get 0.16 ml

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1) Yes!

2) You are almost there. When they say concentration they want to know the amount of drug per unit of volume. The amount is often in grams or mg and volume can be in liters teaspoons etc. To get the concentration of something the basic formula is amount of drug present over the amount of volume it has.

Ex: I have a 50 mg vial of medication and it is a 2 mL vial. I want to know what my drug concentration is so I take the amount of medication: 50mg and divide by the amount of space it takes up(volume). 50/2 = 25mg/mL

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The second question seems to be a big problem for me because I dont know where to start. When it says the final volume is 3ml, does that mean that cefazolin is 0.5ml?

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so would it be 1000 divided by 3? 333.3

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i think this is a terminology question, not a math problem.

the problem says you have one gram of cefazolin in three ml-- that's what final volume means. it's what you have when you've added the liquid to the powder, giving you a vial of liquid medication that is ready to draw up to inject. you have three ml of it.

so now, how do you know how much there is in one ml?

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yes, divide the 1000mg by three, giving you 333mg per ml.

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Are you sure? Question says in EACH milliliter. sounds like it should be 111 ml

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Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.

NO.....If you have 3 cc of solution that has 1000mg of medicine in it.......how much medicine(how many miligrams) would be in each 1cc.

So you have

1000mg

3cc

and you want to know how many X? mg per 1 cc

X? mg

1cc

How many mg do you have per 1 cc?

1000 divided by 3 equals........

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it says your final volume is 3ml. you have 1000mg in 3ml. therefore each ml has 333.3mg in it. you got it right in post #6.

in cases like this i always suggest drawing a picture to help you visualize your problem. or take 1000 pennies, ten bucks (in your imagination), and divide that by 3-- $3.33.

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