Percents and Solutions


Percents in Pharmacy help us determine
the concentration of a solution.
What is concentration?
Concentration

“the strength of a solution as measured
by the weight-to-volume or volume to
volume of the substance being
measured”
Percents

In pharmacy this is indicated in the
following ways:


Weight to volume is: grams per 100 mL
Volume to volume is: mL per 100 mL
For example


If you have a solution of 50% dextrose
in a 1000 ml IV bag, how many grams
of dextrose are there in a bag? You can
solve this by developing a proportion
equation. Since 50% dextrose means
there are 50gms of dextrose in 100ml
the equation would be:
X g divided by 100 ml = 50 g divided by 100 ml
You could also. . .

Convert the percent to a decimal. In a
solution of 50% dextrose, there are .5 g
of dextrose per ml:


50 g/100 ml = 0.5 g/ml
You can then multiply 0.5g by the total
number of milliliters.

X=0.5 g times 1000= 500 g
Now. . .


Using the same bag of Dextrose,
How many ml will give you 10 gm of
Dextrose?
20 ml- WHY? Well. . .

The proportion equation is. . .

X ml/10 g = 100 ml/50g

Solve for X
Practice Problems- Percents

You have a 70% dextrose solution. How
many grams in:

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50 ml of solution=______
75 ml of solution=______
20 ml of solution=______
You have a 50% dextrose solution, how many
ml will give you:



25 g of dextrose = _______
35 g of dextrose = _______
10 g of dextrose =________
Answers
1.
2.
3.
4.
5.
6.
35 gms
52.5 gms
14 gms
50ml
70 ml
20 ml
Percents

You have a liquid that contains 12
mg/10ml. What percent is this liquid?
Percents

In pharmacy this is indicated in the
following ways:


Weight to volume is: grams per 100 mL
Volume to volume is: mL per 100 mL

Remember that 1 gram = how many
milliters?

1 gm= 1000 mg so . . .


0.012gm = 12 mg Right?
Which means the same concentration
has

0.012 gm/10 mL

But you need to find the percent and the
percent needs to be by 100 mL Right?



You can multiply the ratio by 10 and
then you have:
0.12gm/100 mL
Which would translate to 0.12%
solution or liquid.
Percents and Solutions

The Physician wants a 35 % solution of
dextrose 1000 mL. You have a 50%
solution of dextrose 1000 mL. How will
you make up what the physician wants?
Percents- TPN

This is common when administering
TPN (Total Parenteral Nutrition) to
patients.


(TPN is when you can give patients all of
their nutrition needs through an IV or
central line).
You would have =
x volume needed/ want %= volume Prescribed/ Have %
TPN problem






So . . .
Volume needed = x ml
Want % = 35 % dextrose
Volume Prescribed = 1000 ml
Have % = 50%
So the formula here is –

Xml/35%= 1000ml/50% (solve for x)
TPN problem

Which would mean 700 ml of dextrose
50% will give me the 350 g of dextrose
I will need in my solution. Howeverthe doctor ordered 35% in 1000 mL
what do I do?
TPN
You will still need to add sterile water qs
ad until you have a total solution of
1000 mL as ordered by the physician.
Milliequivalents: mEq


Electrolytes are substances that
conduct electrical currents and are
found in the body’s blood, tissue
fluids, and cells.
Some common electrolytes:






NaCl= Sodium Chloride
MgSO4= Magnesium Sulfate
KCl= Potassium Chloride
K Acetate= Potassium Acetate
Ca Gluconate= Calcium gluconate
Na Acetate= Sodium Acetate
mEq



Concentrations of Electrolytes are shown as
milliequivalents (mEq) per mL or mEq per L.
A mEq cannot be converted into the metric
system.
A 0.9% solution of one electrolyte will have a
different mEq value than a 0.9% solution of
another because mEq values are different for
different electrolytes.
Why are they different?

mEq are based on each electrolytes
atomic weight and electron properties
known as valence (the number of
positive or negative charges on an ion).
Example



A solution calls for 5mEq of Na that you
have in a 1.04mEq/ml solution of NaCl.
How many ml of it do you need?
What do you do?
Talk in your groups and see who can
get the answer.
Answer

4.8 mL, Why?
Common Saline Solutions




0.9% NaCl
0.45%
0.2%
3%
Example TPN

A TPN order calls for the amounts on
the left (including additives) to be made
from the items on the right on the next
slide. The total volume is to be 1000mL.
How much of each ingredient do ou
need to prepare this TPN?
TPN Example
TPN order
Aminosyn 4.25%
Dextrose 25%
On hand
Aminosyn 8.5% 1000ml
Dextrose 70% 1000mL


Additives:
KCl 20 mEq
MVI 10 ml
NaCl 24 mEq
KCl 2mEq/10ml
MVI 10 mL
NaCl 4.4mEq/ml 20 ml
We have to figure out each
one individually first



Aminosyn- Using the Percent solutions
Formula of volume wanted and volume
neededXml/4.25%=1000ml/8.5%
Which equals= 500ml of aminosyn
8.5% is needed.
Dextrose

Using the percent Solutions Formula:

Xml/25% =1000/70%
(x volume needed)/(want %) = (Volume prescribed)/(have %)

357 mL of dextrose 70% is needed
KCl


Use a proportion equationxml/20mEq = 1ml/2mEq

10 ml KCl are needed
MVI

You need 10 ml of MVI and you have 10
Ml of MVI so you add the 10 ml of MVI.
NaCl

Use a proportion equation:

Xml/24 mEq = 1 ml/4.4 mEq

5.45 ml of NaCl is needed
Sterile Water




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Add qs ad for volume of 1000 ml
Water needed = 1000 ml minus all other
ingredients
Aminosyn 500 ml
Dextrose 357 mL
KCl 10 ml
MVI 10ml
Na Cl 5.45 ml
TOTAL= 882.45 ml
Sterile Water

1000- 882.45=

117.55 ml of sterile water
Percents and Solutions

A TPN order calls for the amounts on
the left (including additives) to be made
from the items on the right. The total
volume is to be 250 ml. How much of
each ingredient do you need to prepare
this TPN?