# Medication Calculation Question

1. I've got this question and can't figure it out. Any of you math whizzes care to take a stab at it??

Ordered Bretytol 5mg/kg IV stat over 45 minutes. The drug is supplied as Bretyol 500 mg per 10ml ampule. The patient weighs 150lbs

Dilute the drug to 50ml. Using a microdrip set, what is the flow rate in gtt/min

I've figured out the patient gets 340.90 mg and at 10ml the patient gets 6.8ml

After that I'm lost.

The correct answer is 67gtts/min but I'm not sure how to get there.

Joined: Sep '05; Posts: 178; Likes: 166
SRNA; from US
Specialty: Anesthesia, CCRN, SRNA

3. Well yes, you have 6.8 ml but it tells you to dilute it in 50 ml, so maybe that is where you are confused.

volume x drip 50mlx60 gtt

--------------------------------------------------- = 66.6

time 45 min
4. That didn't post right.
volume x gtt divided by time.

50 ml x 60 divided by 45 min = 66.6 or 67 drops/min
5. believe it or not, all the information about the bretytol in this problem is really unnecessary. this problem boils down to a very simple ratio. the only important information that you are given is that you need to give 50cc of whatever complicated solution they are asking you to make over a 45 minute period of time. this is simply:
50ml / 45 minutes = xml / 60 minutes which when you cross multiply becomes 45x = 3000, or x = 66.67 or 67 (rounded off)
with microdrip tubing that is the same as 67 drops a minute.
6. to tell you the truth you have me confused. the above posters seem to be giving the pt the entire 50 ml (or 500mg of the drug) when the pt is only suppose to be getting 5mg/kg or the 341 mg of the drug (regardless of what the drug is diluted in). if i am wrong, please let me know i am on the wrong train of thought. i thought that the pt would need 341mg and the drug was being offered in 500mg/50ml.
7. don't the pt need just 6.8ml of medication from the ampule? then you inject it to the 50ml mini infusion bag to dilute it, right? then you piggyback it?
8. that makes perfect sense. i was thinking dilute first and then take out what you need. not sure why i thought that way, but sure did.
9. It says " dilute the drug to 50 ml". That is where the number came from to those who still are thining of the 6.8 ml.
10. Yes, well you see that is the red herring in this entire question. After you go through the trouble, as the OP did, of figuring out that you only need 6.8mL of the Bretylol solution, it tells you to then dilute it to a total solution of 50mL and deliver it over 45 minutes. That's the "trick" part of the question designed to really trip you up. If you really went ahead and calculated that out, you had to add 43.2mL of what to make the 50mL? That was the first thing that set up a red flag for me. Then, I realized that the Bretylol came in the same liquid amount as they wanted the final dose for the patient to be mixed in. Another red flag. Go ahead and try to work out the question if you like. You'll have calculations all over the place. However, it boils down to one simple thing that is being asked: You are to give a drug mixed into a total solution of 50mL over 45 minutes. What is the flow rate using a microdrip set? You have to read these problems carefully! Draw pictures to help explain what is being asked if you have to. My opinion: it's a poorly written problem designed to specifically trick the student.
Last edit by Daytonite on Oct 10, '06
11. Yes, you could do that, but then you'd have a total of 56.8mL of solution to deliver to the patient over 45 minutes making the infusion rate with microdrip tubing 76 gtts/minute which is not the correct answer. You have to work within the parameters of the question as it is asked.