Dosing question help =)

[Kuriin, BSN, RN]

I have a medication calculation exam coming up and I would like some input from my fellow students, as well as the expertise of the knowledgable nurses! The question itself is simple; however, the use of rounding is throwing me off! I was told to never round weight and to use the calculations from the exact weight to continue the problem. In any case, here is the question:

Order: Granisetron (Kytril) 10mcg/kg, 30 minutes before chemo

Infuse: 1mg over 60 seconds

Patient weights 140lbs

The weight comes out to 63.63 repeating. Without removing the numbers, I multiply by 10 to get 636.36 repeating. I do my formula of 1000/60*636.4 (rounded)/x.

I get 38 seconds.

The book has me round the weight up to 64, which would be an even (and clean) 640mcg.

But, this comes to my predicament in that I was told to NEVER round weight. I would love some input. :)

The book also has me round down the medication from 640mcg to 600mcg. I've never personally seen this, so I would love some help.

[RN403, BSN, RN]

The way the book has you round may just differ from the way your instructor wants you to round. The book has you round the weight up to the nearest whole # while your instructor does not want you to round the weight at all.

This is how I was taught as well and my answers always differed from the book. You might just c

clarify the answers you are getting with your instructor just to ensure those are the answers they are looking for.

I know all of these rounding rules are frustrating, hang in there and good luck on your exam.

[Kuriin, BSN, RN]

Have you seen the latter part, as well? The book rounded the actual ordered medication from 640mcg to 600mcg, which then the answer would be 36 seconds.

[RN403, BSN, RN]

Hmm, I have personally never seen an answer rounded like that. I am a fairly new nurse and cannot think of a rationale behind their rounding. I even just Googled it and could not reach an answer. I'm stumped. Hopefully someone will come along with an answer for us, I say us, because I am now interested to know their reasoning as well.

If I come across an answer to your question or think of anything I will let you know.

[Kuriin, BSN, RN]

I just asked one of my classmates and she got it, so it must be because (and I do apologize for not putting this info down) of part B of the question:

b: How many milligrams is the order?

She rounded the 636mcg down to 600mcg (0.636 -> 0.6). Part C then uses the 0.6mg for the entire answer. I STILL don't understand why, lol, because that would change the actual order by 36mcg and have a decrease of 2 seconds in terms of infusion time.

[RN403, BSN, RN]

Oh, that makes much more sense then.

Okay, so if you were to round by the book's standards:

140lbs/2.2kg = 63.636 kg

then you would take the 63.636kg (or 64kg per the book) x 10mcg and get 636.36 mcg (640mcg )

This would round to 640 mcg per the book's rounding

you would take the 640mcg/1000mcg = 0.64 mg * 60 seconds which would give you 38.4 (38) seconds.

If you round it how your instructor wants you to round it:

then you would take the 63.636kg x 10mcg and get 636.36 mcg which would round to 636 mcg per your instructor's rounding

you would then take the 636 mcg / 1000 mcg = 0.636 mg * 60 which would still give you 38 (38.16) seconds.

The 0.636mg would actually round to 0.64mg in the end and you would still end up with 38 seconds. I'm not sure about the reasoning behind rounding to 0.6mg unless you are supposed to round the nearest tenth per your instructor's rounding rules?

[Kuriin, BSN, RN]

Honestly, no idea. LOL. I am going based on what the book shows and it rounds the 0.636 to 0.6.