Help! The teacher's answers are different from mine?

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Erythromysin 250 mg in 100 ccD5W to infuse over 1 hour. The I.V. tubing delivers 20 gtt/ml. Calculate gtt/min? I got 83.3 but her answer that she gave us was 33.

I am so afraid of failing drug cal tomorrow. We had only 2 days of class where she went over chapter 7 and 8, which is on Monday and Tuesday. Friday she handed out calculation worksheet to us while we were in fundamentals. The test is on Tuesday (tomorrow). We actually were in Fundamentals, not her class so barely got to ask questions. This seems unfair. we needed another day to review.

Specializes in Behavioral Health/Psychiatric Nursing.

This is kind of late for your test, but for what it's worth:

100mL ÷ 60min = 1.6666 mL/min

1.666mL/min x 10gtt/mL = 33.333 gtt/min

Round to 33gtt/min

Convert cc to mL first. Convert hours to minutes. The 250mg is not relevant to this question, they sometimes do this to test how well you can pick out the important details. Do not round until you have your answer, and drops are always calculated to the nearest whole number.

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mg (wt) and ml (volume)are not the same. 250 mg is unnecessary info to solve the problem, the dilute solution d5w is another unnecessary info, but that is how questions are constructed to exercise not only math skills but critical thinking.That being said, cc to ml can be the same. To solve the problem use ml unit. Don't sweat it

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You are letting yourself get flustered. The strength of the medication has already been added to the bag so is therefore not part of your calculation. This is what the posters above are trying to get you to see.

100ml of fluid divided by 60 minutes X drip rate of 20.

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I hate dosage calcs!

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3 hours ago, TyCo2015 said:

I hate dosage calcs!

Why? Don't let the fact that you're doing dosage calculations, medication math, or whatever else you want to call it make these problems harder than they are. When you remove the descriptors, dosage calculations are nothing more than basic math.

You will hear and read much about formulae to solve these, and there are formulae to solve most of these, you would be best served to learn dimensional analysis (DA), as there are no problems that can't be solved using DA. If you are unfamiliar with, or just want more information on DA, Brad, a retired pharmacist, has written a book on dosage calculations. Although this book was primarily written for pharmacy technicians the process is the same. The book is included as an attachment to the following post:

Best wishes.

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Specializes in being a Credible Source.
On 1/20/2020 at 3:08 PM, Beaue said:

Erythromysin 250 mg in 100 ccD5W to infuse over 1 hour. The I.V. tubing delivers 20 gtt/ml. Calculate gtt/min? I got 83.3 but her answer that she gave us was 33.

I am so afraid of failing drug cal tomorrow. We had only 2 days of class where she went over chapter 7 and 8, which is on Monday and Tuesday. Friday she handed out calculation worksheet to us while we were in fundamentals. The test is on Tuesday (tomorrow). We actually were in Fundamentals, not her class so barely got to ask questions. This seems unfair. we needed another day to review.

As stated, the answer is 33

Did you perhaps use the 250mg somewhere? If so, take another look because that's irrelevant to the question.

Before you start busting out formulae or consider dimensional analysis, think about what's actually happening *physically* in the real word.

Think about it like this...

  1. Start by considering only the volume (cc or mL... same exact thing... 1 cubic centimeter = 1 milliliter...)
  2. Now think about how many drops it takes to make up that volume (I really loathe the "gtt" abbreviation because it's just one more thing to create a bit of cognitive dissonance)
  3. Now consider the timing... that is, the duration of the infusion
  4. Now think about the rate of the infusion that will get the intended volume infused over the requisite duration.

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This is a stupid easy problem made more complicated by extra info. Here is literally the easiest way to calculate these:

1) Always first calculate how many TOTAL gtts you will be infusing. Well, you're doing 20gtts in each mL and the med you're giving is in a solution of 100mL total. So, 20 x 100 = 2000 gtts

2) Now, how much time does the doc want for the infusion? 1 hr? Great. But the DRIP RATE is given in MINUTES. We all know there are 60 minutes in 1 hr.

Divide 2000total gtts by 60 total minutes = 33.33...

Note: Drip rates are almost always in MINUTES. Sometimes the total time will be over 8 hours. In this case you would first need to divide by total # of hours THEN divide that by 60 to get the total MINUTES.

Lastly, you can't have 0.33 of a drop, so you have to ROUND to 33. The correct answer is 33.

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The answer is 33.3333. Your Teacher is correct. 100cc/60min X 20tt = 33.3

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Specializes in NICU.

stop blaming the teacher and open your books and figure it out.Take it step by step,you have to know this, so try again.

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On 1/20/2020 at 3:08 PM, Beaue said:

Erythromysin 250 mg in 100 ccD5W to infuse over 1 hour. The I.V. tubing delivers 20 gtt/ml. Calculate gtt/min? I got 83.3 but her answer that she gave us was 33

250mg is the concentration of the drug in 100cc. Do not use the drug concentration because that's not the problem is asking for. It's asking for the solution.

1cc =1mL

----> 100cc=100mL

(100mL/60minuted)(20gtt/mL)=33.3333=33 gtt/minute.



You wanna do extra work, look at this and please don't freak out.

https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_Chemistry_-_The_Central_Science_(Brown_et_al.)/04._Reactions_in_Aqueous_Solution/4.5%3A_Concentration_of_Solutions

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Your 250mg is already mixed in the 100cc or 100mL solvent.

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Specializes in Psych, Corrections, Med-Surg, Ambulatory.

My brain does not do formulas. So I just break down the problem to bare bones. How many millilitres do I want to infuse? How many drops does that work out to? How many minutes do I have to infuse all those drops?

1000ml x 20gtts = 2000gtts. Divide those 2000gtts by 60 minutes and you get 33.3333. Round it up or down.

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