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Pharmacy IV drip calculation

by John D
(Indio, CA)

An IV has been ordered to run for 4 hours at 10gtt/min with a drop factor of 20 gtt/ml. The solution in the bag is 750mg of active drug dissolved in .5L of D5NS. How many mg of the active drug will the patient receive in two hours?
A. 45 mg
B. 60 mg
C. 90 mg
D. 120 mg

Reply :
by Jerry

This is question #1 from free quiz #4. It has a fair amount of fluff to de-code thru. It's a good example of what you coud expect on the PTCB or ExCPT exam. So, first write down all necessary factors, and then work toward the unknown variable.

Here's one way to do it:

First, convert hours to minutes:

2 Hours = 120 Min

Then, Figure out how many drips will drop in that time :

120 Min x 10gtt/min = 1200gtt/duration

Next Divide the drips by how many make up an mL :

1200gtt ÷ 20gtt/mL = 60mL

Lastly, Set-up a quick conversion against the IV solution :

750mg - - - - X
-------- = ---------- cross-multiply for X
500mL - - - 60mL

Now, your turn...

X =

Comments for Pharmacy IV drip calculation

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IV Drip Calculation
by: Brad Wojcik, Pharm D

Here is another way. Remember, all you are being asked to do is change the units of the given into the units of the answer using ratios which are equal to 1.

2 h(60 min/h)(750 mg/500 ml)(10 gtt/min)(1 mL/20 gtt) = 90 mg.

You might ask how 10 gtt/min equals 1. If someone asked you to put 10 drops of the IV solution into a container, you would simply count out 10 drops and put it in the container. If they asked you to run the IV for 1 min into another container, you would end up with 10 gtts also. 10 gtt/10 gtt = 1.

by: Anonymous

i'm still confused on where the 500 mL came from?

reply to 500 mL question
by: Brad Wojcik

The 500 mL came from the 0.5L in the problem.

by: Anonymous

When converting hours to minutes why did you convert 2 hours and it says 4 hours???

Reply to 2 hours question
by: Anonymous

We used 2 hours because the question was how much drug would the patient receive in 2 hours.

by: Anonymous


Another way to answer
by: Dr Sheikh

Time / Volume = 10 gtt/ min ÷ 20gtt/ml = 0.5 ml/min

750mg / 500ml x 0.5 ml / min = 0.75 mg / min

0.75 mg / min x 120 min = 90 mg

Is the IV bag not emptied after 4 hours?
by: Anonymous

Isn't the question asking for mg of the drug? If the patient only gets 90 mg in 2 hours, then that's only 180 mg in 4 hours (the duration of the bag.) Doesn't the IV contain 750 mg total?

by: Anonymous

I worked out the problem I came out to 900 as the answer when it should be 90 I worked as shown here .(750mg/500ml)(10gtt/min)(1ml/20gtt)2hr(60min/1hr)

error de cálculo
by: Anonymous

90 mg

Another way to answer:
by: Chelsey

The answer is 90mg, C.

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