Help with dosage calc problems!

sh1901 · Jan 28, 2009

In your post is gr grains or grams? That makes a difference. Usually if gr comes before the number (like gr 1/16) it is grain, and typically gm is for gram. But your question has the gr both before and after numbers, so I just want to be sure.

Thanks!

miss_c · Jan 28, 2009

It is grains I suppose I posted exactly how the question reads.

sh1901 · Jan 28, 2009

Ok, I only did the first problem and I got the same answer as you, so maybe someone needs to set both of us straight!! Here is what I factored (I rounded numbers where necessary):

I calculated that gr 1/16 would be equal to 4.1mg and that if I have 4.1mg in 1ml, then I would have to administer 61ml to give 250mg. There are approximately 5ml per tsp, so that would be 12 tsp, and then 3tsp per tablespoon, so 4 tablespoons, which is DOUBLE what your answer key is telling you.

UGH!! :banghead:

shrimpchips, LPN · Jan 28, 2009

Ok, I only did the first problem and I got the same answer as you, so maybe someone needs to set both of us straight!! Here is what I factored (I rounded numbers where necessary):
I calculated that gr 1/16 would be equal to 4.1mg and that if I have 4.1mg in 1ml, then I would have to administer 61ml to give 250mg. There are approximately 5ml per tsp, so that would be 12 tsp, and then 3tsp per tablespoon, so 4 tablespoons, which is DOUBLE what your answer key is telling you.
UGH!!

I also got the answer of 4 tablespoons. Maybe there was a misprint or a mistake?

Btw, are grains still used? I have yet to see that unit of measurement on a MAR/medication sheet.

miss_c · Jan 28, 2009

I also got the answer of 4 tablespoons. Maybe there was a misprint or a mistake?
Btw, are grains still used? I have yet to see that unit of measurement on a MAR/medication sheet.

I have found several other mistakes on our practice sheet. That makes the practice very :banghead:

I'm not sure if grains are still used or not! I just know they sometimes show up on our tests!

Thanks for taking the time to review my question!

Daytonite, BSN, RN · Jan 28, 2009

a medication comes in gr. 1/16 per ml. you are to give 250 mg. how many teaspoons will you administer. when i worked the problem i got 12 teaspoons. the answer key says 2 tb! i don't get it!

when i worked the problem as is, i get 4 tblsp as the answer. i worked the problem backwards. i think there was a typo and the problem probably should have read "a medication comes in

gr. 1/6

per ml." when i work the problem with that figure i get something close to the correct answer.

dose on hand: 1 grain/6 x 60 mg/grain x 1/1 ml = 10 mg/ml

dose desired: 250 mg

250 mg (dose desired)/10 mg (dose on hand) x 1 ml (amount dose on hand comes in) = 25 ml

25 ml/1 x 1 tblsp/15 ml = 1.666 tblsp, rounded up up to 2 tblsp

you are to administer 1/8 gr of a medication. available is 125 mg/5 ml. how many ml will you administer? i get .414 ml. the answer key says .325 ml.

they are using 1 grain = 65 mg as the conversion factor. also, before working the problem, turn the 1/8 grain into a decimal and save yourself a lot of headache. 1/8 grain = 0.125 grain as a decimal. now,

0.125 grain

(dose desired)

/125 mg

(dose on hand)

x 5 ml/1

(amount the dose on hand comes in)

x 65 mg/1 grain

(conversion factor)

=

0.325 ml

(amount to give)

sh1901 · Jan 29, 2009

My instructor for dosage calculations said that they do still use grains sometimes for narcotics because they are so strong and given in lower dosages. Who knows if that is the case in "real life" though.

Daytonite - Thank you so much for the post - if you got the same answer with the information given it makes me feel a bit better about my skills in that arena.

Oz2 · Jan 29, 2009

We learned that 1 grain was 60 mg. It's my dosage calculation book too. Weird.

1andrea1 · Jan 29, 2009

In our program we have to pass a math exam with a 92% each to semester to stay in. We just took ours and for both of the questions I would use:

Desired amount/Have on hand x Quantity

so for the first one you have 1/16 of a grain, I would convert that to mg first by taking 1/16 x 60 and you get 3.75 then take the 250mg and divide it by 3.75 then multiply by 1ml, I ended up with 67 ml, convert 67 ml to oz and you get 2.23 oz round down for 2 oz.

for the second question I converted the grains to mg by taking 1/8 x 60 and ended up with 7.5 mg. Take this and plug it into the problem

7.5/125 x 5ml = 0.3 ml.

I have found that using D/H x Q works for most problems after all of the conversions are done.

About the 60 or 65 mg for 1 grain, we were taught to use 65 for aspirin and 60 for everything else.

Sorry for the mistake, I actually converted the first problem to ounces instead of teaspoons, maybe that is why it is wrong on your sheet.

shrimpchips, LPN · Jan 29, 2009

We learned that 1 grain was 60 mg. It's my dosage calculation book too. Weird.

gr 1 can equal 60 or 65mg. In the clinical setting, call the pharmacy to verify this. It also depends on the medication; 65mg = gr 1 is the best conversion; the most noteable of these are Tylenol and aspirin (gr x = 650mg) (from Calculate With Confidence: 4th Ed. by Deborah Gray Morris).