# What in the drug calculation is this???

Published

We were doing drug calculations in Pharm today and I think the instructor was dead wrong, but Im not the kind of student to correct an instructor's wrongs especially this one because she is EXTREMELY combative and defensive so I just sent all my classmates a note on Blackboard telling them that I think her calculation was wrong or she missed a step or something....I didn't tell them what yet because I wanted to be sure so here is the problem:

The suggested range for a medication is 3-5mg/kg/day. The client weighs 175 lbs. What would be the maximum dosage the client receives in 24 hours?

How I calculated it was: 79.55kg * 5 mg = 397.75mg / (three 8-hour intervals) 3 = 132.59 mg

I may be wrong but another instructor told us to calculate the time by breaking it down into intervals. Im not sure where that instructor got that from but it is what she gave us...now the two seem to be colliding and no one knows what the right answer is. Can anyone help? What is right here, what is wrong here?

I did the calculation and got the same answer you did.

Specializes in Utilization Management.

I'm not really sure what your question is - the problem asks for the maximum dose in a 24-hr period, which would be 397.75mg. If it asked for the maximum dose PER dose, then the answer would be 132.58mg.

Great Anna, Im glad! Man, I hope more people come in here and do it. Because the instructor left the answer at 397.75....I was like no that can't be right...what about the time? I have another one has well that I feel a step in calculations was left off. So Anna do u understand the whole concept behind the three 8-hour interval thing because I do not I just know it was what was told!

I'm not really sure what your question is - the problem asks for the maximum dose in a 24-hr period which would be 397.75mg. If it asked for the maximum dose PER dose, then the answer would be 132.58mg.[/quote']

Ok I think I get what you're saying.....gosh, we have two instructors telling us two different things and boy is it clashing!!!! But your calculation is right....I just did not understand the reason for the "three 8-hour intervals" when calculating a problem asking what the max dose would be in 24 hours.....

Oh my gosh guys, Im such a doof, lol! I went back and divided 397.75 by 79.55, my answer.....5. That's the max dose. @Boog'sGirl man that is a lot of breaking it down so I guess I am wrong! But hey this is what our co-instructor told us....to divide by the 8-hour intervals....

Specializes in CNA.
But hey this is what our co-instructor told us....to divide by the 8-hour intervals....

Your co-instructor is incorrect. If you run into this question on other tests, just answer the question and don't use your crazy instructor's interpretation.

What would be the maximum dosage the client receives in 24 hours?

The 24 hours part key. They want to know how much medication the pt is getting in a 24 hour period.

If someone asks, "what is the maximum single does if the pt receives the med tid?" then you break it down. Without knowing the dosage schedule (once, bid, tid, qid) how could you determine the maximum single dose?

Thanks guys and yes that does make sense...still it's so confusing. Well, here is one that I am just generally having problems with:

Zaroxolyn is on hand in gr 1/6 tablets. The prescribed dose is 20 mg.

Im not sure if I am supposed to be using the 1 mg=1/60 grain formula or what...if so I got 18, but somehow I feel it's wrong...any help on that one?

Specializes in CNA.
Thanks guys and yes that does make sense...still it's so confusing. Well, here is one that I am just generally having problems with:

Zaroxolyn is on hand in gr 1/6 tablets. The prescribed dose is 20 mg.

Im not sure if I am supposed to be using the 1 mg=1/60 grain formula or what...if so I got 18, but somehow I feel it's wrong...any help on that one?

Yeah, they like to use a couple different approximations for grains to mg and not explain why.

As you know, one conversion is gr I = 65 mg.

Hey, but there is another one. gr X = 600 mg

Those two don't really work out exactly. I just used 1/60 for all meds except aspirin and Tylenol then it's 1/65.

The only time you would divide your original problem by 3 is like they said...if it asked per DOSE and clearly stated the patient is getting it Q8H or TID. But since it just said for the whole day, multiply that 5 times the kg(weight of the pt) and you get your answer.

Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.
Thanks guys and yes that does make sense...still it's so confusing. Well, here is one that I am just generally having problems with:

Zaroxolyn is on hand in gr 1/6 tablets. The prescribed dose is 20 mg.

Im not sure if I am supposed to be using the 1 mg=1/60 grain formula or what...if so I got 18, but somehow I feel it's wrong...any help on that one?

They are still teaching the apothacary? You will NEVER use it. BUT......Here is a great drug calulation site http://www.dosagehelp.com/facebook_like.html

Specializes in Aspiring for a CCRN.

Q: Zaroxolyn is on hand in gr 1/6 tablets. The prescribed dose is 20 mg. How many tablets would you give to patient?

*gr i = 60 mg

1. Let's find out how many mg in a gr 1/6 tablet (some of you already did this in your head, but let's write this out):

(gr 1/6) x (60 mg/ gr i) = 10 mg *This tells us that grain 1/6 contains 10 mg

2. If one gr 1/6 tablet contains 10 mg, then how many tablets would you give to patient to fulfill the dosage of 20 mg? (again, let's write this out)

20 mg x (1 tablet/10 mg) = 2 tablets.

*For those who prefer a straight-shot DA:

tablets = (1 tablet / gr 1/6) x (gr i / 60 mg) x (20 mg) = 2 tablets