Per Cent concentration drug calculations

[8jimi8]

Doing my P2 homework has unearthed a weakness in my drug calculation prowess.


The question: If you have a 4% solution of medication how many mls do you add to 500cc if you want a final concentration of 4mg/ ml


here's my rationale: 1% solution = 1 gram / 100 cc

to arrive at a final concentration of 4 mg/ml i need a total of 2000mg over the 500 ml.

typing it out it seems pretty simple that the answer is 50cc, right?!

 

[Sandog]

Is that all the info given? Seems like we need to know what molarity the solution is, in other words, what is the concentration of the solution, 4% of what?

How did you get 1%= 1 gram? 1 gram is quite a large amount of solute.

Maybe I am thinking too much like chemistry here, but something seems missing.

 

[8jimi8]

Is that all the info given? Seems like we need to know what molarity the solution is, in other words, what is the concentration of the solution, 4% of what?

How did you get 1%= 1 gram? 1 gram is quite a large amount of solute.

Maybe I am thinking too much like chemistry here, but something seems missing.

That is a number i pulled off of the internet. we'll see if its right.

My instructions are " dosages must be perfect."

 

[Sandog]

Lets examine this, you are saying 1% = 1 gram per 100cc or 1g/100ml since 1cc=1ml. 1 molar = 1 mole per liter and 1 mole = 1 gram so at 1g/100ml means we have 10g at 1 liter or a 10 molar solution which seems like a real strong solution. In all fairness I am not a medic or nurse so I am not familiar with all the dosing issues but I do know gen chemistry and I keep thinking 4% of what?

Since no one else spoke up I thought I would interject. Just trying to get the full picture as I am fairly good with stoichiometry...

 

[8jimi8]

i dont know about your molar conversion,

from what I found on the internet the constant is 1 gram / 100 cc = 1% solution.

further reduced to 10mg / 1 ml.

MedicRob found some website backing up that number, so i'm gonna roll with it.

if that supposed number is correct, my calculations shouldn't be wrong.


the equation is actually pretty simple if you have the 1% solution figure memorized

 

[Sandog]

I am certain my molar conversion is correct:
1 molar = 1 M = 1 mole/liter and moles = 1g/mol, 100cc = 100 ml so 1000ml = 1 liter thus if you have 1g/100cc then 1000cc(1 liter)/10g is 10 moles or a 10 molar solution.

My only assumption can be is that the 4% is a standard percentage that should be known otherwise I think the question is bogus. I am sure someone will set me straight so I am ready for mud in my face :sad:

 

[Aidey]

While chemistry is not one of my strong areas, I think you are misapplying moles in this situation.

1 gram = 1 mole of a pure substance. Since medications aren't pure substances 1g =/= 1 mole.

I think.

 

[Sandog]

While chemistry is not one of my strong areas, I think you are misapplying moles in this situation.

1 gram = 1 mole of a pure substance. Since medications aren't pure substances 1g =/= 1 mole.

I think.

Molarity = moles of solute/1 liter of solution

1 mole of a substance means there is 1 gram of substance, a 1 molar solution means there is 1g of substance dissolved in a 1 liter of solution eg.
1g of poop/1L = 1 molar of poop solution.

 

[8jimi8]

Molarity = moles of solute/1 liter of solution

1 mole of a substance means there is 1 gram of substance, a 1 molar solution means there is 1g of substance dissolved in a 1 liter of solution eg.
1g of poop/1L = 1 molar of poop solution.

the misapplication being that the mole is 10x the amount of solvent we are talking about.

1% solution is equal to 1 gram in 100 Milliliters.


if a mole = 1gram / 1liter...

 

[medicRob]

Percent solutions all are 1000mg/100cc.

2% = 20mg/cc,
5% = 50mg/cc,
5.5% = 55mg/cc,
etc...

4% = 40 mg/cc

 

[Sandog]

the misapplication being that the mole is 10x the amount of solvent we are talking about.

1% solution is equal to 1 gram in 100 Milliliters.


if a mole = 1gram / 1liter...

Now I think I got myself confused... Arggg

 

[Sandog]

Percent solutions all are 1000mg/100cc.

2% = 20mg/cc,
5% = 50mg/cc,
5.5% = 55mg/cc,
etc...

4% = 40 mg/cc

Okay, I see, that was the magic number I was not aware of.

So that would imply a 1 molar solution? 100% = 1000mg = 1g yes?



Thanks ...

 

[8jimi8]

Okay, I see, that was the magic number I was not aware of.

Thanks ...

It took him a long time to tell me the same thing. I've been bugging him about that for like 6 hours.

apparently i'm to be "rickrolled" for even suggesting the theme tonight.

 

[Aidey]

Stolen from Wikipedia's article on saline.

The solution is 9 grams of sodium chloride (NaCl) dissolved in 1 liter of water. The mass of 1 milliliter of normal saline is 1.0046 grams at 22°C [3][4]. The molecular weight of sodium chloride is approximately 58 grams per mole, so 58 grams of sodium chloride equals 1 mole. Since normal saline contains 9 grams of NaCl, the concentration is 9 grams per liter divided by 58 grams per mole, or 0.154 moles per liter.

If you post below applies to medications saline would have 9 moles per liter, which it doesn't.

I am certain my molar conversion is correct:
1 molar = 1 M = 1 mole/liter and moles = 1g/mol, 100cc = 100 ml so 1000ml = 1 liter thus if you have 1g/100cc then 1000cc(1 liter)/10g is 10 moles or a 10 molar solution.

My only assumption can be is that the 4% is a standard percentage that should be known otherwise I think the question is bogus. I am sure someone will set me straight so I am ready for mud in my face :sad:

 

[Sandog]

Yes, you are right, I see my chem has gotten rusty, I think I will get some sleep now, obviously I need it.

 

[mgr22]

Doing my P2 homework has unearthed a weakness in my drug calculation prowess.


The question: If you have a 4% solution of medication how many mls do you add to 500cc if you want a final concentration of 4mg/ ml


here's my rationale: 1% solution = 1 gram / 100 cc

to arrive at a final concentration of 4 mg/ml i need a total of 2000mg over the 500 ml.

typing it out it seems pretty simple that the answer is 50cc, right?!

To go from a 4% solution (40mg/cc) to 4mg/cc (0.4%), you're decreasing the concentration by a factor of 10, which means you'd need 10 times the solvent (5,000cc). Of course, we'd never do that -- just as we'd never put 20,000mg (20g) of a med in a 500cc bag (well, maybe if Rev. Jim Jones were a nurse... . This sounds like an incredibly contrived problem, or someone made a mistake.

 

[medicRob]

It took him a long time to tell me the same thing. I've been bugging him about that for like 6 hours.

apparently i'm to be "rickrolled" for even suggesting the theme tonight.

In my defense, I was drinking... I was being attacked with dosage calculation during my drinking hour!

 

[8jimi8]

In my defense, I was drinking... I was being attacked with dosage calculation during my drinking hour!

Fair enough, but you know i'll have to pay it forward to someone we treat at bonnaroo.

 

[medicRob]

Fair enough, but you know i'll have to pay it forward to someone we treat at bonnaroo.

Get ready, cause it is gonna be crazy. You'll love it though.

 

[8jimi8]

Get ready, cause it is gonna be crazy. You'll love it though.

I freaking tried to contact the Tennessee Board of Nursing. Those lame-os are closed for the holiday...