# Medication calculation problem

Published

I need help please working out how to answer this question. I'm happy for not being given the answer but a solution of working this out PLEASE. I have exam end of the week.

Your pt is prescribed Ampicillin 500mg IVI q6h as prophylactic antibiotic cover post operatively. Ampicillin is reconstituted within 10ml sterile water for injection. Ampicillin is diluted to 100ml of 0.9 norm saline IVI and infused over 30min

AU stock, 1000ml Ampicillin vial (powder) reconstituted the Ampicillin power with 10ml sterile water for injection. This makes a reconstituted strength of 1000mg/10ml.

calculate total vol of fluid in pt burette.

Here are some words of wisdom from my favorite clinical instructor from nursing school:

"Look it up."

Jojo489 - I wouldn't of asked for help if I hadn't already tried working out the answer. I've got every other question right in the mock test and got this one wrong and the answer doesn't match up to my calculations and I have gone over and over it. I know it's maybe as simple as 1,2,3 and again I'm not asking for the answer just help with the formula to see if I have been on the right track and maybe their answer is wrong I don't know.

Specializes in MICU.

can you show us what you got and how you set it up to see why you didnt get it right

Yes - my formula was SR./SS x V = 500x10=5000/ 5000 devide by 1000 = 5. 5ml is my answer but their answer is either a,95 b,90 c,100 d,50ml so I'm defiantly missing something in my working out.

Reread your problem. What is the volume of ampicillin that you have? What is the final volume that you need to dilute to?

You're on the right track.. you would withdraw 5mL from the vial for the correct dose.. but then what would you do with it?

Would you give those 5mL IVP over the 30 min OR would you add it to some other fluid to infuse over 30 min?

Specializes in NICU.

In the problem you have 3 things: 500 mg vial of Ampicillin, 10ml sterile water, and bag of 100ml normal saline. Once you get the proper dose of Ampicillin in your syringe, what do you do with the syringe and the normal saline?

Specializes in Acute Care, Rehab, Palliative.

You need to get rid of the information that doesn't matter. How much NS containing ampicillin are you infusing? Think about it carefully. They want the total volume of fluid. It wouldn't be 5 ml.

Eliminating all the (literally) useless, extraneous information, we have:

Ampicillin is diluted to 100ml of 0.9 norm saline IVI and infused over 30min

calculate total vol of fluid in pt burette.

Looks like the answer is right there staring you in the face. :)

See, this is the problem with memorizing bunch of formulas for med arithmetic. You have a whole bunch of slots to plug numbers into, but if you don't know what the question is asking, you think you have to put something in all of them, and maybe you don't.

There's actually no calculation to do here at all. All you had to do was .... read and think.

I will grant you that it's possible that they are referring to the amount of NS in the burette before you add the ampicillin, in which case it's 95cc of saline and 5cc of the drug as reconsitituted. But the question SAYS, "total volume of fluid in burette." That's 100cc, isn't it? Because it says the stuff is usually diluted to (not "added to")(whatever mg it is) in 100cc.

Yep, sometimes it is that simple. This is a question designed to find out whether you can read, not whether you can do multiplication and division. :)

You will find that you will often be asked test questions (on actual tests and in actual life) that look like they're asking you one thing but they're really asking you something else entirely. Nursing is like that. Count this as your first lesson in critical thinking, that is, putting it all together before you answer. As Swami Beyondananda says, "Don't just do something, sit there!"

Specializes in Pedi.
Yes - my formula was SR./SS x V = 500x10=5000/ 5000 devide by 1000 = 5. 5ml is my answer but their answer is either a,95 b,90 c,100 d,50ml so I'm defiantly missing something in my working out.

You have 5 mL of medication that you have to draw up, that's correct. But since your original problem says that the Ampicillin has to be diluted to 100 mL, what would you do with this 5 mL of medication? What will your total volume be once you've done this?