# Dosage Calculation

1. We practiced in class for our dosage calculation exam coming up Mon Jan 31. We got the problems from "CLinical Dosage Calculations Made Easy." The problem is that the instuctor made a mistake of solving one of the prob. I didn't look at the answer key at the back of the book till I went home. I email back my instructor Friday night only to realize she doesn't answer emails after 3pm Friday and during the weekend. Please if you know how to do the steps please Help Me... thanks

The whole class has 1.25mL and the book has
1.33mL. Can you please tell me where to incorporate the fraction in the
problem.

"Order: morphine sulfate 10mg IM prn for pain. How many milliliters will you
give."

The dosage on the medication label is 8mg (1/8gr.)/mL.

gr=grain, 1grain = 60mg

Joined: May '04; Posts: 78; Likes: 1
Specialty: Oncology Unit

3. sorry - I got what you did. Must rethink this!
4. I think you have converted your grains to mg wrong. I got 7.5mg = 1/8gr. If you go by (desired/have)*quantity, you have this equation set up...
(10/7.5)*1=1.33mL

To convert my grains to mg, I did this equation...
((1/8)/1)*(60/1)=7.5

(1/8)*60=7.5, not 8.0

Hope that helps you!
5. okay = I don't understand the 8 mg - because gr1/8 is equal to 7.5 mg.

know gr1/60 mg = gr1/8 / x mg
cross multiply
1x = 60 x 1/8
1x = 7.5

so

have 7.5 mg/1ml = need 10 mg/ x ml
cross multiply 7.5x = 10
7.5x/7.5 = 10/7.5
x = 1.33
how's that? Sorry - it took me a while to type out!
6. Quote from WSU_Ally_RN2B
I think you have converted your grains to mg wrong. I got 7.5mg = 1/8gr. If you go by (desired/have)*quantity, you have this equation set up...
(10/7.5)*1=1.33mL

To convert my grains to mg, I did this equation...
((1/8)/1)*(60/1)=7.5

(1/8)*60=7.5, not 8.0

Hope that helps you!
WSU_Ally_RN2B vbmenu_register("postmenu_1054282", true); you have the right answer. The book did it the same way. I look at the answer key and it didn't use the 8mg from the label of the medication. I don't know why. Is anyone out here solving this problem like they do it in chemistry (dimensional analysis) rather than breaking it apart. Dimensional analysis is solving it all at one time
Last edit by Kristy_joyz on Jan 30, '05
7. Well, to do dimensional analysis, you would do it like this....
(10mg/1)*(1gr/60mg)*(1mL/(1/8)gr)=1.33mL

I personally think it's harder to do it this way. If you just convert your grains to mg in the beginning you can use the (desired/have)*quantity formula right away, and don't have to think how to set up dimensional analysis...
8. This may be a stupid question....why would you even mess with grains when on the bottle it states 8mg/ml and your order is for 10mg? I set this problem up at 8mg/ml = 10mg/x, then cross multiply, I came up with 1.25mg.
9. I agree with jamie.. this one is an old dose form that you wont ever see. About the only thing you see ordered in gr is asprin and tylenol. You wont find a morphine vial anywhere that is labeled in gr. If it is,, its probly to old to use safely. I wish they would update some of the math in these books too.
10. Both could be the answer, depending on the figures you use. If you use 8mg, the answer is 1.25.

If you use gr 1/8, which is really 7.5mg, the answer is 1.33. The book made the mistake of putting "8mg (gr 1/8)"....these things are not equal!
11. [QUOTE=Kristy_joyz]We practiced in class for our dosage calculation exam coming up Mon Jan 31. We got the problems from "CLinical Dosage Calculations Made Easy." The problem is that the instuctor made a mistake of solving one of the prob. I didn't look at the answer key at the back of the book till I went home. I email back my instructor Friday night only to realize she doesn't answer emails after 3pm Friday and during the weekend. Please if you know how to do the steps please Help Me... thanks

The whole class has 1.25mL and the book has
1.33mL. Can you please tell me where to incorporate the fraction in the
problem.

"Order: morphine sulfate 10mg IM prn for pain. How many milliliters will you
give."

The dosage on the medication label is 8mg (1/8gr.)/mL.

Ok - Dosage/on hand (x) ml available = X
so 10mg/8mg (x) 1ml = 1.25 rounded to 1.3 ml. The book probably made a misprint- but that is what I got too. My math book has some mistakes in it too.
12. This is how I did it...no reason to even convert the grains....

xml=10mg*1ml/8mg..mg's cancel= 10*1ml/8=1.25ml no rounding. I would bet that the book is wrong. I don't even know why you would have to touch the grains. Dimensional analysis is way to complicated.
13. We were taught that 1 gr = 60 mg for gr < 1; and 1 gr = 65 mg for gr >= 5
(and that we would not find any between 1 & 5). Now, by this, they should have used 1 gr = 60 mg. But, if they used the 1 gr = 65 mg, then you get closer to the 8mg = 1 gr. (Actually, 8.125 = 1 gr.) Looking on the net, it appears the more exact measure is 1 gr = 64.8 mg. (rounded to 100ths)

NurseFirst

[QUOTE=RNToobee]
Quote from Kristy_joyz
We practiced in class for our dosage calculation exam coming up Mon Jan 31. We got the problems from "CLinical Dosage Calculations Made Easy." The problem is that the instuctor made a mistake of solving one of the prob. I didn't look at the answer key at the back of the book till I went home. I email back my instructor Friday night only to realize she doesn't answer emails after 3pm Friday and during the weekend. Please if you know how to do the steps please Help Me... thanks

The whole class has 1.25mL and the book has
1.33mL. Can you please tell me where to incorporate the fraction in the
problem.

"Order: morphine sulfate 10mg IM prn for pain. How many milliliters will you
give."

The dosage on the medication label is 8mg (1/8gr.)/mL.

Ok - Dosage/on hand (x) ml available = X
so 10mg/8mg (x) 1ml = 1.25 rounded to 1.3 ml. The book probably made a misprint- but that is what I got too. My math book has some mistakes in it too.