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Dosage Calc Format Problem

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by S.Christopher S.Christopher (New Member) New Member

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Howdy!

My friend asked for some help with dosage calculation problems, but the format of the last two questions are throwing me off.

Could anyone give me a hand setting up these problems please?

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34 Visitors; 6 Posts

I see that the second to last problem needs grams of calcium, and they forgot to convert mg to grams.

Would it be?
3L x 8.3mg x 1gm = grams
1      1L         1000mg

=40grams?

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34 Visitors; 6 Posts

The last one I think it is asking for me to find the gm/kg.

I have 2.2kb / 230lb = 104.5kg

Then

2tabs x 250mg x 1gm     = grams

             1tab       1000gm

=2 grams

Then I am confused as to what is next.

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2 hours ago, S.Christopher said:

The last one I think it is asking for me to find the gm/kg.

I have 2.2kb / 230lb = 104.5kg

Then

2tabs x 250mg x 1gm     = grams

             1tab       1000gm

=2 grams

Then I am confused as to what is next.

Your friend didn't pay attention to their units when doing the problem. 

For example, they divided 230 lbs by 2.2 lbs and came up with 104.55 lbs.  The patient weighed 104.5 kg not 104.5 lbs.

The correct way to do the problem would be

230 lbs x 1 kg/2.2 lbs = 104.5 kg

Because lbs appears in both the numerator and denominator, you can eliminate lbs in the equations.  You are left with kg in the numerator.

Now you know that a 104.5 kg patient was given 500 mg of the med. 

Another way to say that is the dose was 500mg/104.5kg. 

The question is asking what was the dose in grams/kilogram.  

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3 hours ago, S.Christopher said:

I see that the second to last problem needs grams of calcium, and they forgot to convert mg to grams.

Would it be?
3L x 8.3mg x 1gm = grams
1      1L         1000mg

=40grams?

When you work this type of problem the first thing you should do is to write what you are given (calcium, 8.3 mg/L) on the far left hand side of your worksheet.  Then write what you are asked to solve (g calcium present in the blood) on the far right side of your worksheet.  What steps do you think you need to do to solve this?

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How much calcium is present in the patients 3L on blood. Calcium is measured in the problem in mg, and the answer needs to be in grams.

8.3mg x 3L divided by 1000.

0.0249 grams.

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1 hour ago, Anonymous865 said:

Your friend didn't pay attention to their units when doing the problem. 

For example, they divided 230 lbs by 2.2 lbs and came up with 104.55 lbs.  The patient weighed 104.5 kg not 104.5 lbs.

The correct way to do the problem would be

230 lbs x 1 kg/2.2 lbs = 104.5 kg

Because lbs appears in both the numerator and denominator, you can eliminate lbs in the equations.  You are left with kg in the numerator.

Now you know that a 104.5 kg patient was given 500 mg of the med. 

Another way to say that is the dose was 500mg/104.5kg. 

The question is asking what was the dose in grams/kilogram.  

104.5kg and she takes two 250mg tablets a day.

500mg (2 tabs of 250mg) in grams is 0.5 grams.

So 0.5 grams divided by 104.5 = 4.78

I can't see the rounding instructions, but is that the way to go about that problem?

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12 minutes ago, S.Christopher said:

[...]

So 0.5 grams divided by 104.5 = 4.78

[...]

This isn't correct.  You're not consistent in your units of measure.

ETA: I'm not sure how you're setting these problems up, but if your not using dimensional analysis you really should try and learn it.  And don't try and concert units in your head, or make multiple conversions simultaneously; this leads to the possibility of making a 10 fold mistake, which can be fatal depending upon the medication or patient population. 

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1kg      x  230lbs


2.2lbs

Cancel out the lbs and divide 230 by 2.2 and get 104.5 kg


2tabs   x  250mg  x  1gm   =gm  


               1tab   x 1000mg  

 

tabs and mg cancels out. Reduce 250 to 1, and 1000 to 4.

reduce the left over   2/4 to   2grams.

I am left with 2grams and 104.5kg, but I don't understand what to do from this point on.

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12 hours ago, S.Christopher said:

 

[...]

2tabs   x  250mg  x  1gm   =gm  


               1tab   x 1000mg  

[...]

Rather than starting with 2 tabs, I would start with the total dose 500 mg.  Also, when you post here, rather than posting all in line as you did here, consider posting it as:

(2 tabs / 1) * (250 mg / 1 tab) * (1 g / 1000 mg) = X g

This makes it much easier to follow as you lose alignment when you post in line.

 

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12 hours ago, S.Christopher said:

[...]

I am left with 2grams and 104.5kg, but I don't understand what to do from this point on.

Recheck your calculations.

Once you have the correct dose and patient weight, what do you think you could convert the total dose to g/kg?

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21 hours ago, S.Christopher said:

104.5kg and she takes two 250mg tablets a day.

500mg (2 tabs of 250mg) in grams is 0.5 grams.

So 0.5 grams divided by 104.5 = 4.78

I can't see the rounding instructions, but is that the way to go about that problem?

Use a calculator to divide 0.5g by 104.5.  You won't get 4.78.  You are off by a factor of 1000.

When doing math ask yourself if it makes sense that by dividing 0.5 by 104 that you would get a number BIGGER than you started with.  Of course not.  If you have 1/2 and divide it by 104, your answer is going to be a lot SMALLER than the 0.5g that you started with.

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