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Hi all! I have a question regarding an assignment for "Math for Meds." I have the answers, which are confirmed correct via a given answer key. While, I figured out how to do the calculation, I am confused/concerned about the rational.

Pt with CHF has an order for theophylline 300 mg in 50 mL D5W over 30 minutes. Pt weighs 68kg.

The lable provided states:

This is what I am confused/concerned about:

- the pt is supposed to get 300mg in 30 minutes....

so if I divide the 316.9 by 2 (to account for the 30 minute infusion time) I get 159.8mg

How and why is this safe? Yes 159.8mg is under 300mg (or 319.6 mg for that matter)... so they are not going to "OD" but how is it safe to not receive the 300mg (as ordered)... wouldn't this make the loading dose and/or order ineffective?

Thank you in advance! I am going to ask my professor in the morning, but this is kinda driving my mind bonkers, so I thought I would reach out to the allnurses community.

Again, thank you, I look forward to hearing back from the community.

1 Article; 4,383 Posts

Is the question asking if it's safe to give a 300 mg loading dose over 30 minutes?

And the right answer is "yes"?

(Want to make sure I give you a rationale for the right thing.)

1 Article; 4,383 Posts

Ok, reread, and I think I understand.

Loading dose should be 64.7 mg/kg which ends up being about 300mg, and we like to round.

So you've got 300mg, which is a safe dose.

That has NOTHING to do with the rate or the infusion time.

So in this problem completely forget about rate and time, there's no reason to even consider time unless this question is asking if that's a safe rate of infusion.

8 Posts

Specializes in Geriatrics, Oncology. Has 4 years experience.

the lable provided states:

the order doesn't say anything about it being per hour. the looading dose was ordered as 300mg. you figured 316. that is why the order is safe to give. do you see it. i know i always got hung up on labeling, looks like that is what is going on here.

86 Posts

Thank you so much! For curiosities sake... why does the infusion time not matter? Why does this not affect the effectiveness/ efficiency of the med?

My thoughts clouding my understanding... for example... a pt needs 1 unit of insulin for every 150 carbs ... but the pt only take .5 units... the insulin would not be effective...therefore, it would be an unsafe dose to treat the condition.

Thanks again!

1 Article; 4,383 Posts

Like most nursing students, you're overthinking it. :)

It didn't ask if it was a safe rate (600mg/hr).

1 Article; 4,383 Posts

My thoughts clouding my understanding... for example... a pt needs 1 unit of insulin for every 150 carbs ... but the pt only take .5 units... the insulin would not be effective...therefore, it would be an unsafe dose to treat the condition.

And actually there, it's not "unsafe" just possibly ineffective. Big difference. Not going to help doesn't necessarily equal going to hurt.

59 Posts

Specializes in Critical care (coronary care). Has 14 years experience.

aminophylline(80% theophylline)

infusion dose 500 mg in d5w 500 ml

drug interactions: cimetidine, ciprofloxacin, erythromycin,clarithromycin

safety dosage in special situation:

chf 0.3 mg/kg/h

normal 0.6 mg/kg/h

therapeutic levels: 10-20 mg/l

smoker 0.9 mg/kg/h

59 Posts

Specializes in Critical care (coronary care). Has 14 years experience.

reference:

AACN Essentials of Critical Care

Nursing—Pocket Handbook

2 Articles; 5,114 Posts

sounds like you're not clear on the concept of " loading dose." what's the purpose of theophylline? how does it work? does it need to be kept at a certain blood level (concentration) to be effective? how is that level achieved, and, most importantly, what would make it decrease over time?

when you can describe all these, you'll have a better idea if this concept, and you will understand why there was no time frame asked for or needed in your original question. and you'll never make that mistake again!

86 Posts

You each are so amazing! I am truly grateful for your time and help! I have a lot more to do tonight r/t med calculations and infusions rates... Are there any site you would recommend for a reference? Some of the problems are not covered in our text (how wonderful haha)!

Also, for the fun of it, what are you specialties? Why did you choose your area of practice?

I originally wanted to do OR until i did my clinical rotation. Now I am thinking Hospice... Regardless of where I end up... I know and I will specialize in wound care! I have had 30 knee surgeries on 1 leg. Hence the name "PayitForward"

I am SO excited to be on Allnurses.com!! :)

Take Care!

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