Daytonite...Need your help with this calculation!

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We had three questions based on one label, so if you get the first wrong, you'll get all three wrong.

The label was Ancef 400 mg/5mL. Reconstitute with 90 mL. The vial said that there was 100 mL (when constituted).

The first question asked how many grams was in 5 mL once reconsituted. (I had 0.04g/5 mL)

The second asked how many 800 mg doses there was in this vial. (I had 1 dose)

The third asked how many mL per 200 mg. (I had 25 mL)

As you can see all of my answers are based on the fact that I had thought it was 800 mg/100 mL for the entire vial.

I had thought that the vial would actually be one dose:

For example, since the vial said that it was 100 mL reconstituted, I had subtracted the 90 mL (the amount added), leaving 10 mL @ 400 mg/5 mL. However, it seems as though I may have taken it too far and may have read too much into the label.

According to the instructor it would be 10 doses.

100 mL X 400 mg = 40,000 = 8,000 mg

1 5 mL 5

8,000 mg X 1 dose = 10 doses

800 mg

I'm just so confused about the reconstituting...did I read too much into it?

Any help is greatly appreciated.

Kris

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Students often get hung up on questions involving reconstituting drugs. In my experience, the problem is that they panic and make the problems/calculations more complicated than they need to be. The concentration of the drug (dosage) and the quantity in the vial are two entirely different things, and that's where you went awry. Also, reconstituting the solution and calculating dosages are two entirely different processes. Tthat 90 ml that you use to reconstitute has nothing to do with any dosage question and will just confuse you if you think about it, so put it right out of your mind!

The 400 mg/5ml is a constant, regardless of how much fluid you're talking about. When you reconstitute the Ancef and wind up with 100 ml of solution, each 5 ml of that 100 ml contains 400 mg of Ancef. The only numbers that matter are the dosage concentration (400 mg/5ml) and total quantity in the vial (100 ml).

Since 1000 mg = 1 Gm, 400 mg would = 0.4 Gm.

Since 400 mg = 5 ml, then 800 mg (400 mg x 2) would = 10 ml (5 ml x 2). Since there is 100 ml of solution in the vial, 100 ml/10 ml = 10 doses (of 800 mg) in the vial.

Again, if 5 ml = 400 mg (still the original, constant, concentration -- it never changes :)), and you want 200 mg of Ancef (1/2 of 400 mg), then 5 ml/2 (1/2 of 5 ml) = 2.5 ml.

Best wishes!

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Specializes in med/surg, telemetry, IV therapy, mgmt.
the label was ancef 400 mg/5ml. reconstitute with 90 ml. the vial said that there was 100 ml (when constituted).

how many grams was in 5 ml once reconsituted?

how many 800 mg doses there was in this vial?

how many ml per 200 mg?

elkpark explained it pretty well. here's the math:

how many grams was in 5 ml once reconsituted?

400 mg/5 ml
(dose on hand)
x 1 gram/1000 mg
(conversion factor)
=
0.4 grams/5 ml

how many 800 mg doses there was in this vial?

400 mg/5 ml = 800 mg /
x
ml,
cross multiply to get
x
=
10 ml
(amount per dose)

then, since each vial has 100ml (when constituted):

100 ml
(amount on hand)
/10 ml
(amount per dose)
=
10 doses

how many ml per 200 mg?

400 mg/5 ml = 200 ml/
x
ml,
cross multiply to get
x
=
2.5 ml

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THANK YOU BOTH VERY MUCH!:bowingpur:bowingpur...Yes, I did make it more complicated than it really was. I appreciate your working and explaining the problem. Looking at it makes me understand more of where I went wrong. Thanks again!

Kris

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Specializes in N/A.

Daytonite,

First of all, I am a new member to allnurses.com but have been viewing many post that have helped me out in my journey through nursing school. I am in my 4th semester and am having a rough time with pediatric medication calculations. I have two problems below that I can't figure out how to set up as to answer all four questions. Was wondering if you could assist?

1. Dr. order is Ampicillin 225mg IV every 4 hours. The pt weighs 16.6 kg. The recommended dose is 50-100 mg/kg/day. The guideline states 10 ml over 30 minutes. The pharmacy sends a vial with 250 mg Ampicillin in the vial. (Hint: after dilution you pull up 5cc of fluid).

A. Is this the appropriate dose for the pt?

B. How much will you prepare from the vial?

C. How much fluid will you have in the volume control device?

D. What rate will you set the pump for the medication and flush (flush is always 20 ml)?

2. Dr. Order is Gentamicin 78 mg IV every 8 hours. The pt weighs 26.4 kg. The recommended dose is 7-7.5 mg/kg/day. The guideline states 1mg/ml over 30 minutes. The pharmacy send a vial with 100mg/2ml.

A. Is this the appropriate dose for the pt?

B. How much will you prepare from the vial?

C. How much fluid will you have in the volume control device?

D. What rate will you set the pump for the medication and flush (flush is always 20 ml)?

Any help would be appreciated.

Thanks, Shaq23

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where does it say that the 400 gm/5 ml is POST reconstitution?

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Specializes in N/A.

Morte,

Thanks so much for your reply. Since I am knew to allnurses, I made a mistake in posting my problem on top of another students problem. Your question of "where does it say that the 400 gm/5 ml is POST reconstitution?" came from another students post. I am sorry for any confusion I may have caused.

MY problem is what I wrote below:

I am in my 4th semester and am having a rough time with pediatric medication calculations. I have two problems below that I can't figure out how to set up as to answer all four questions. Was wondering if anyone could assist?

1. Dr. order is Ampicillin 225mg IV every 4 hours. The pt weighs 16.6 kg. The recommended dose is 50-100 mg/kg/day. The guideline states 10 ml over 30 minutes. The pharmacy sends a vial with 250 mg Ampicillin in the vial. (Hint: after dilution you pull up 5cc of fluid).

A. Is this the appropriate dose for the pt?

B. How much will you prepare from the vial?

C. How much fluid will you have in the volume control device?

D. What rate will you set the pump for the medication and flush (flush is always 20 ml)?

2. Dr. Order is Gentamicin 78 mg IV every 8 hours. The pt weighs 26.4 kg. The recommended dose is 7-7.5 mg/kg/day. The guideline states 1mg/ml over 30 minutes. The pharmacy send a vial with 100mg/2ml.

A. Is this the appropriate dose for the pt?

B. How much will you prepare from the vial?

C. How much fluid will you have in the volume control device?

D. What rate will you set the pump for the medication and flush (flush is always 20 ml)?

Thank you so much Morte....I hope I cleared up any confusion I have caused in my post.

Shaq23

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