# Dosage Calculation Question

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I'm having a problem with the following question:

Order: Pepcid (famotidine) 20mg IVPB q. 12h.

The label on the 4ml. vial reads 10mg/mL. The manufacturer recommends adding the famotidine to 50mL of D5W and infusing the medication over 60 minutes. At how many microdrops per minute will you set the IVPB solution to infuse?

This is exactly how the question is written. I am at a total loss here. Do I first figure out how many mg need to be given in 60 min? Am I crazy in thinking that I need tubing calibration info in order to ultimately solve this problem?

I'm so lost

26 Posts

Ok, I think I may have figured it out. A microdrop set equals 60gtt/min. So I have taken 54ml x 60gtt/min and divided that by 60 min. to come with an answer of 54gtt/min. I'm still not 100% sure I'm correct because I'm thinking there is still more calculating to be done. I need to think about this some more.

10 Posts

Ok I'm not sure if this is right. But I used what I had on hand first. 10mg per 1ml over 50mls=500mg. Then u take the 500 total volume and divide by 60= 8.333333 rounded off to 8 drops per min. The 4ml is to throw u off. Let me know what you come up with.

4,104 Posts

Specializes in NICU. Has 8 years experience.

If you need 20 mg and the vial reads 10 mg/ mL, how many mL do you draw out of the via. HINT: the vial contains 4 mL which is 40 mg.

Take that number and add 50 mL for the D5W.

Divide that number by 60 to get ml/min

multiply that number by the tubing drop factor and you have your drops/min.

26 Posts

If you need 20 mg and the vial reads 10 mg/ mL, how many mL do you draw out of the via. HINT: the vial contains 4 mL which is 40 mg.

Take that number and add 50 mL for the D5W.

Divide that number by 60 to get ml/min

multiply that number by the tubing drop factor and you have your drops/min.

Thanks, Don! You hit on what I did eventually figure out, that your total mL will be 52, not 54 because the order is for 20mg, not 40mg. I knew there was something I was missing at first, it just took me a few extra minutes to figure out what it was.

phillygirl: The way I set up this problem is: total volume 52 x gtt factor 60 gtt/min divided by total time 60 min. to get a final answer of 52 gtt/min. Just like I learned on DosageHelp.com, which I discovered thanks to the helpful people of this site

gtt/min = total volume x gtt factor

total time---->

I can't get "total time" line up right, but I hope you get the idea.

1,204 Posts

just as a point of order --- please know that a microdrip set is 60 gtt/mL NOT 60 gtt/min.. :)

1 Article; 7,349 Posts

Specializes in Pedi. Has 16 years experience.
Ok I'm not sure if this is right. But I used what I had on hand first. 10mg per 1ml over 50mls=500mg. Then u take the 500 total volume and divide by 60= 8.333333 rounded off to 8 drops per min. The 4ml is to throw u off. Let me know what you come up with.

No. You don't have 10 mg/mL for all 50 mL of fluid. The medication is 10 mg/mL and OP needs to add 20 mg (2 mL) to 50 mL of fluid. The final concentration is WAAAAYYYY less than 10 mg/mL since she will have 20 mg/52 mL. 52 mL needs to be infused in one hour. Microdrip tubing is always 60 gtts/mL.

So your final problem would be:

52 mL/hr x 60 gtts/mL x 1 hr/60 min leaving you with 52 gtts/min. With microdrip tubing, the rate in mL/hr and gtts/min is always the same.

21 Posts

Specializes in Dialysis. Has 5 years experience.

--------------------'

1 20

----x. =2

10

50+2=52

52×60 gtt.

-------------------- = 52 gtt/min

60 min.

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