How The Hell Do U Do Reconstitution Math Please Please Explain Please

My school was very fortunate to teach an entire class just on nursing Math. I have listed some forumulas to help you and if you know the formula, you cannot possibly screw it up.

First, you always start out with the ORDER of the physician. That's an easy number to pull from a problem:

Basic concept:

Amount of solusion x the Strength = The amount of pure drug.

Sample question:

How many grams of sodium chloride would you need to prepare 100 mL of a 20% solution?

First, you know you'll eventually need 100 mL...so you write that down first., then set up the second half of the problem like a percentage, as 20% of 100 is 20. The 20% will have the DRUG in it.

So calculate:

100 mL (which is your order) x 20 g/100 mL = 20g

So you write it out: You need 20 grams of sodium chloride to prepare a 100 mL of a 20% solution.

Tip: If you get something like mg, etc...all you do is convert it over to grams and use the SAME formula.

Now, for reconstitutions:

Just remember this formula:

amount prescribed x strength prescribed = amount of stock

Strength of stock

Again, start out with your order in this sample question:

How would you prepare 1,000 ml of a 25% solution from a 50% stock solution?

Tip: Use the same percentages, and plug it into your formula...divide out the denominator first, and then do the rest of the math:

1,000 ml x 25 ml/100 ml = Amount of stock

50 ml/ 100 ml

* This fraction is hard to write on this computer....when you write down 1,000 ml x 25 ml/100 ml draw a huge line under this entire thing, and then write 50 ml/100 ml....and divide 50 by 100 first.

So the calculation equals 500 ml.

The answer is:

You would take 500 ml of the 50% stock solution and add water (or whatever the problem calls for) to the level of a 1,000 ml.