# dosage calculations questions: Who's wrong, me or the study guide?

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Hi, I've never posted before, but I need help now. I am trying to test out of the dosage calculation course. I have a few answers that are different than the ones on the study guide and can't seem to contact anyone that can go over them w/me. Those of you who enjoy math and want to help, I would really appreciate it!

The first one is a two part question:

Order:Ampicillin 1g added to 50mL of NS q12hr. Infuse over 45 min

Supply: Ampicillin 5g/10mL

IV Tubing: 60gtt/mL

What volume will the nurse draw up to deliver ordered medication?

Answer: 2mL (I agree w/this)

What is the gtt/min? Answer: 66gtt/min

(Shouldn't the answer be 69gtt/min since the new volume is 52mL? My calculations are : 52mL/45min X 60gtts/1mL = 69gtts/min)

Please straighten me out if I'm wrong!!

Thanks ahead of time for anyone's input

105 Posts

Has 6 years experience.

Gee you sound right on that one, but I wouldn't worry about it too much because so many of the study guides are full of errors. Pay more attention to the examples that are worked through in the textbook instead.

105 Posts

You are right. Study guide is wrong. :)

6 Posts

Gee you sound right on that one, but I wouldn't worry about it too much because so many of the study guides are full of errors. Pay more attention to the examples that are worked through in the textbook instead.

I don't have a textbook. A friend who's in nursing suggested I challenge the course by taking the CCT test. I understand the abbreviations and know the conversions. If I can pass it (w/an 85 or better) that will be one less thing for me to worry about during clinicals. I heard there is a lot of homework involved and no credit is given for the course.

I have another if you or anyone else wants to look at it.

Order: Dephenhydramine 3 mg po q6h

Child's weight: 3,923 grams

Manufacture recommended dose is 1.2 mg/kg/qid not to exceed 200 mg/day total dose

Supply: Diphenhydramine 2.25 mg/5mL

What volume will the nurse administer?

Answer: 10mL (this seems to be calculated according to mfr dose)

My answer: since the ordered dose is 3mg that is what I used. My calculations are: 3mg x 5mL/2.25 mg = 6.7mL

82 Posts

Even the supposed "right" answer in the book is wrong...

60gtt/ml x 50ml/45min = 66.66666 or 67 gtt/min -not 66!

I agree with your answer though - and in reality, the difference is negligible.

And as far as the diphenhydramine - I would give the dose ordered unless it fell significantly above recommended dosage, in which case I would question the order. Obviously this one doesn't fall into that category! You are right.

Good for you for getting advanced credit! Good luck with your studies~

26,410 Posts

What ever book that you are using, throw it out.

How can it tell you that the answer is 10 ml when that would be giving the child 4.5 mg?

Forget that book, you are only going to get more confused. There are much better out there.

48 Posts

Hi, I've never posted before, but I need help now. I am trying to test out of the dosage calculation course. I have a few answers that are different than the ones on the study guide and can't seem to contact anyone that can go over them w/me. Those of you who enjoy math and want to help, I would really appreciate it!

The first one is a two part question:

Order:Ampicillin 1g added to 50mL of NS q12hr. Infuse over 45 min

Supply: Ampicillin 5g/10mL

IV Tubing: 60gtt/mL

What volume will the nurse draw up to deliver ordered medication?

Answer: 2mL (I agree w/this)

What is the gtt/min? Answer: 66gtt/min

(Shouldn't the answer be 69gtt/min since the new volume is 52mL? My calculations are : 52mL/45min X 60gtts/1mL = 69gtts/min)

Please straighten me out if I'm wrong!!

Thanks ahead of time for anyone's input

The difference between 66 and 69 gtt/min is completely negligable. When you are calculating drops per minute, do not add the mL's of Ampicillin you are adding to the NS, unless it is a very large amount (which probably would not happen).

The reason for this is that gtt/min are not a perfect science. You only use them if the IV is not on a pump (unlikely, unless you work ER). You monitor the gtt/min by eye, and the rate can change even if the patient so much as raises their arm. That is why the study guides never add in the extra amount that you will add, because it makes no difference in the long run.

Double check with your teacher just to be sure... but in general, if they ask you to calculate gtt/min on problems like this, calculate it from the original amount of fluid they gave you in the problem.

Don't throw your study guide out, that's what helped me pass the test!

I can't help you with the second question. I got the same answer you did. And even if they went by the mfr, the answer would be 10.5, not 10. Again, ask your teacher for help.

6 Posts

The difference between 66 and 69 gtt/min is completely negligable. When you are calculating drops per minute, do not add the mL's of Ampicillin you are adding to the NS, unless it is a very large amount (which probably would not happen).

The reason for this is that gtt/min are not a perfect science. You only use them if the IV is not on a pump (unlikely, unless you work ER). You monitor the gtt/min by eye, and the rate can change even if the patient so much as raises their arm. That is why the study guides never add in the extra amount that you will add, because it makes no difference in the long run.

Double check with your teacher just to be sure... but in general, if they ask you to calculate gtt/min on problems like this, calculate it from the original amount of fluid they gave you in the problem.

Don't throw your study guide out, that's what helped me pass the test!

I can't help you with the second question. I got the same answer you did. And even if they went by the mfr, the answer would be 10.5, not 10. Again, ask your teacher for help.

Thanks for your input everyone. It sounds like I'm being nitpicky about this stuff, but the test is computerized so it doesn't have room for error. And like I said before, I don't have a teacher or textbook because I'm challenging the class so I don't have to take it. I have a few more problems but I don't want to bore you all. Thanks again!

26,410 Posts

The difference between 66 and 69 gtt/min is completely negligable. When you are calculating drops per minute, do not add the mL's of Ampicillin you are adding to the NS, unless it is a very large amount (which probably would not happen).

The reason for this is that gtt/min are not a perfect science. You only use them if the IV is not on a pump (unlikely, unless you work ER). You monitor the gtt/min by eye, and the rate can change even if the patient so much as raises their arm. That is why the study guides never add in the extra amount that you will add, because it makes no difference in the long run.

Double check with your teacher just to be sure... but in general, if they ask you to calculate gtt/min on problems like this, calculate it from the original amount of fluid they gave you in the problem.

Don't throw your study guide out, that's what helped me pass the test!

I can't help you with the second question. I got the same answer you did. And even if they went by the mfr, the answer would be 10.5, not 10. Again, ask your teacher for help.

If there is 2.25 mg in 5ml, then how do you come up with 10 ml or higher for 3mg dose? That would be over 4.5 mg per dose.

Unfortunately, when it comes to taking an exam, there is a difference between 66 or 69 gtts. The instructors want to make sure that you are doing the calculations properly. There is only one correct answer, not a range when doing calculations, especially when it comes to trying to place out of a class.

26,410 Posts

There are also different study guides on the market.

48 Posts

If there is 2.25 mg in 5ml, then how do you come up with 10 ml or higher for 3mg dose? That would be over 4.5 mg per dose.

Unfortunately, when it comes to taking an exam, there is a difference between 66 or 69 gtts. The instructors want to make sure that you are doing the calculations properly. There is only one correct answer, not a range when doing calculations, especially when it comes to trying to place out of a class.

To clarify... it would be over the ordered dose... but I think the answer came from the manufacturer's recommendation, not from the doc's order. I would go with the doctor's order of course, and question him on it if necessary. Which is why I don't understand why the study guide said 10mL was the correct answer, because as you said then a dose of 4.5mg is administered.

No, there's not a range, and yes there is a difference on the test. But like I said all my teachers and clinical instructors have specifically told us to not add the 2mL (or whatever volume it may be) that you are adding to the original fluid. Just use the original amount. If you have 150mL of NS and you are adding 5mL of the prescribed medication, calculate the drip rate with 150mL, not 155.

Do you know any nursing instructors? Even if they're not your teacher you can ask them what they think about it, or maybe an advisor can put you in touch with someone who has already taken that test.

26,410 Posts

To clarify... it would be over the ordered dose... but I think the answer came from the manufacturer's recommendation, not from the doc's order. I would go with the doctor's order of course, and question him on it if necessary. Which is why I don't understand why the study guide said 10mL was the correct answer, because as you said then a dose of 4.5mg is administered.

No, there's not a range, and yes there is a difference on the test. But like I said all my teachers and clinical instructors have specifically told us to not add the 2mL (or whatever volume it may be) that you are adding to the original fluid. Just use the original amount. If you have 150mL of NS and you are adding 5mL of the prescribed medication, calculate the drip rate with 150mL, not 155.

Do you know any nursing instructors? Even if they're not your teacher you can ask them what they think about it, or maybe an advisor can put you in touch with someone who has already taken that test.

The question said to give 3 mg, you have to go by that number. Not the drug companies recommendation for claculations. It is only telling you that you should not be giving more than this amount taking into account the weight of the child.

And you are correct by saying that you calculate the drip factor on the original fluid amount, not when adding the drug. However, this can change in a critical care area with some very potent medications that you are titrating. To get the exact and specific factor, you can actually remove fluid from the bag to still give you the exact amount. Think of when you adding drugs to a buretrol for either a child or peds patient for dopamine or dobutamine. You add the drug and then fluid to make 100 ml...........Same as when using a bag with a larger amount of fluid, you just remove the fluid if the calculation is that critical to the patients survival. But you will always go by original mount of fluid.

(p.s. Ampicillin will never come as the question stated, it is not stable for more than one hour, so it will have NS added to the vial on the floor.)

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