Question about a question on dosage calculation test

hypocaffeinemia, BSN, RN · Dec 10, 2008

Grain is part of the outdated and soon to be (if not already) banned by JCAHO apothecary system.

One grain is equal to anywhere from 60-65 mg depending on your source. Now you see why it's being banned.

The way the problem was written, I have no idea what the 200 is in reference to: 1/200 of a grain (~0.3mg)? What it's diluted in? Dunno.

avahnel, ASN, RN · Dec 10, 2008

I had a similar question on my pharm exam I took yesterday

Doctor's order: atropine gr 1/150 IM now Available: atropine 0.4 mg/mL How many mL will you administer Correct answer: 1mL

I took 60/150 and got 0.4 then devided the 0.4/0.4=1mL

so for 1gr/200 (60/200=0.3) then devide ordered by have (0.3/30=0.1) if that is per 1ml then 0.1x1=0.1mL

So I think the answer would be 0.1 mL

Daytonite, BSN, RN · Dec 10, 2008

my friend had taken the dosage calculation test this morning and after she took it, she called me hysterical because there was a question on there she wasn't sure about. the doctor ordered 1 grain/200; availible is 30 mg,how much should you give the patient? i already took my test and got 100% on it, but being a prenursing student, i didn't know what this meant exactly. she said that there was no unit on the 200. was this a typo on the test or can you tell me how to figure this out. thanx alot!

there was a unit on the 200. it was a fraction (1/200). a unit label is never afixed to the denominator of a fraction; always to the numerator. in this case, the "1". thus, "1 grain/200". to do this by dimensional analysis the fraction needs to be flipped in order to cancel out both the "mg" and "grain" labels. i think that typing "1 grain/200" may have been a hint for the students doing the calculation that way.

200/1 grain

(dose on hand)

x 30 mg tablet/1

(dose to give)

x 1 grain/60 mg

(conversion factor)

=

100 tablets

(amount to give)

approaching this another way. . .1/200th grain is

0.005 grain

.

30 mg coverted to grains using 60mg/grain as a conversion is 30mg/60mg or

0.5 grains

. then, doing dose desired (0.5 grains) divided by dose on hand (0.005 grains), you get the same 100 tablets.

i would so not give this drug and be on the phone calling this doctor if this were a real life situation.

hypocaffeinemia, BSN, RN · Dec 10, 2008

there was a unit on the 200. it was a fraction (1/200). a unit label is never afixed to the denominator of a fraction; always to the numerator. in this case, the "1". thus, "1 grain/200". to do this by dimensional analysis the fraction needs to be flipped in order to cancel out both the "mg" and "grain" labels. i think that typing "1 grain/200" may have been a hint for the students doing the calculation that way.
200/1 grain
(dose on hand)
x 30 mg tablet/1
(dose to give)
x 1 grain/60 mg
(conversion factor)
=
100 tablets
(amount to give)

approaching this another way. . .1/200th grain is
0.005 grain
.
30 mg coverted to grains using 60mg/grain as a conversion is 30mg/60mg or
0.5 grains
. then, doing dose desired (0.5 grains) divided by dose on hand (0.005 grains), you get the same 100 tablets.
i would so not give this drug and be on the phone calling this doctor if this were a real life situation.

you had the dose ordered and the dose on hand backwards.

if the doc ordered 1gr/200, if you divide 60 by 200 to convert to milligrams, you see he ordered 0.3 mg. if the dose on hand is 30 mg, you're looking at the opposite problem: instead of 100 tablets you're needing 1/100th of a tablet- another impossibility.

either way, the problem doesn't add up.

Daytonite, BSN, RN · Dec 11, 2008

So, what does "The doctor ordered 1 grain/200" mean? OP, you want to clarify that, please.

RNJune2010 · Dec 11, 2008

How I did it:

(1/200)gr * 60mg/1gr*tablet/30mg = 0.01 tablet

Can't give 0.01 of a tablet