Drug calculation issue

This is a standard Dose/Have X Quantity problem. Or, D/H X Q. It is confusing. The reconstitution part. The problem isn't meant to confuse you. The problem is simply confusing. Eventually, you'll have to look at slip of paper that comes with the drug during clinical. You'll have to figure this out. You've seen them. The hand outs that come with drugs. Tiny lettering. And, plain confusing. Anyway.

To make it easier, consider the concentration of the drug/mL after you add the normal saline. Your focus when determining how much to administer is the following:

The dose the doctor orders

The concentration of drug/mL after you reconstitute. Or, the drug/mL (Have) is the number that will be used to figure out how much you'll administer

And, the quantity. Both problems below have 1 mL as quantity.

Problem 1

Order (Dose): Ancef 500 mg

Have: 330 mg/mL after reconstituted

Quantity: 1 mL

Following the standard: D/H X Q format

500 mg / 330 mg/mL = what?

Then multiply the above answer by 1.

The final answer is how many mL you administer.

Problem 2

Order (Dose): Ampicilline 500 mg

Have: 250 mg/mL after reconstituted

Quantity: 1 mL

Following the standard: D/H X Q format

500 mg/ 250 mg/mL = what?

Then multiply the above answer by 1.

The final answer is how many mL you administer.

I hope this helps.

I use formulas, and the fomula for this would be:

total drug.....ordered drug

_________ = _________

total volume...ordered volume

1000mg.......500mg

_______ = ________

3ml................X

cross multiple to get 1000x=1500

x=1.5

sorry about the ....'s, it wouldn't post in the right place without them

I just answered this question yesterday when you posted it in another thread: https://allnurses.com/general-nursing-student/reconstitution-drug-calculation-526988.html#post6434452

You need to ignore how much is available and the volume you use to reconstitute. The only things you need to know are the ordered dose, and the concentration of the medication.

order: Ampicillin 500 mg

available: Ampicillin 500 mg

Directions: Reconstitute with 1.8 mL sterile water for a concentration of 250 mg/ml

their answer is 2ml.

All you need is the information in bold. Forget everything else. So then your question reads: Ampicillin is supplied as 250mg/mL. How many mL's do you give if the ordered dose is 500mg?

Then you just follow your standard medication formula: Desired dose / Available concentration x available volume.

500mg (desire dose) / 250mg (available concentration) x 1mL (available volume) = 2mL of medication

For your second problem the only information you need is:

order ancef 500 mg

concentration of 330 mg/mL

500mg (desired dose) / 330 mg (available concentration) x 1mL (available volume) = 1.5 mL

Thank you all SO MUCH !

I am really lost on a particular type of problem, and have looked all over the place and can not seem to find a formula that fits these problems. No matter how I set these problems up I can not get the answers that the worksheet says are correct. I suspect that some of the info in the question is thrown in to confuse, and man has it ever worked in my case. All help GREATLY appreciated

a) order : Ancef 500 mg

on hand: 1 G

reconstitute with 2.5 mL normal saline to

yield 3 ml worth of a concentration of 330 mg/ml

answer is 1.5ml

You may try a little visualization.

You receive an order for 500 mg of Ancef. Wise nurse that you are, you know the Ancef is on the med cart. You see a bottle of Ancef with the following lable on it:

------------------------------|

ANCEF 1G |

|

add 2.5 mL of normal saline |

Reconstitution: 330 mg/1mL |

------------------------------|

After you read the label, you know that the Ancef must be reconstituted by adding 2.5 mL of normal saline. After you reconstitute the Ancef, the bottle contains a total concentration of 330 mg/mL.

You now ready to solve your problem with the concentration in the Ancef bottle of 330 mg per 1 mL

The order is 500 mg. The reconstituted Ancef is 330 mg per 1 ml Ancef. So, how would you solve it?

You may try a little visualization.

This is sooo important in drug calculations. Yet so many students get caught up in the numbers, and not what they mean.

I hate the dose ordered/on hand way of solving problems...i always get confused when people use that.

500mg X 1mL

_____ ____ = 1.5mL/dose.......................................................................................

1 dose 330mg

I just find this way much simpler than thinking of what goes where....maybe im weird like that?