10. Calculations II: Compounding

Question 1

Common IV Fluids: Normal Saline content

Answer 1

0.9% NaCl in water

Question 2

Common IV Fluids: 1/2 NS content

Answer 2

0.45% NaCl in water

Question 3

Common IV Fluids: 1/4 NS content

Answer 3

0.225% NaCl in water

Question 4

Common IV Fluids: D5W content

Answer 4

5% dextrose in water

Question 5

Common IV Fluids: D20W

Answer 5

20% dextrose in water

Question 6

Common IV Fluids: D5NS

Answer 6

5% dextrose and 0.9% NaCl in water

Question 7

Common IV Fluids: D51/2NS

Answer 7

5% dextrose and 0.45% NaCl in water

Question 8

Rx “Prepare a 3% w/w coal tar preparation; qs with petrolatum to 150g.”
How many grams of petrolatum is required to compound this prescription?

Answer 8

(0.03*150g) = 4.5g coal tar
150g - 4.5g = 145.5 g petrolatum

Question 9

Percent weight-in-volume (%w/v) units

Answer 9

g per 100 mL

Question 10

Percent volume-in-volume (%v/v) units

Answer 10

mL per 100mL

Question 11

Percent weight-in-weight (%w/w) units

Answer 11

g per 100 g

Question 12

Express 0.04% as a ratio strength

Answer 12

0.04 / 100 = 1 part / x
x = 100 / 0.04 = 2500
1:2500

Question 13

50mg of drug in 50mL of solution
Express conc as a ratio strength

Answer 13

50mg = 0.05g
0.05g/50mL = 0.1g / 100mL = 1 part / x
x = 100/0.1 = 1000
1:1000

Question 14

Ratio strength to percentage strength math

Answer 14

% strength = 100 / ratio strength

Question 15

Percent strength to ratio strength

Answer 15

Ratio strength = 100 / % strength

Question 16

Express 0.00022% (w/v) as part per million (PPM)

Answer 16

0.00022g/100mL = x parts / 1,000,000
X = 2.2 PPM

Question 17

Water has a specific gravity of ___

Answer 17

1; 1g water = 1mL water

Question 18

____ is the ratio of the density of a substance to the density of water

Answer 18

Specific gravity

Question 19

Substances with a specific gravity <1 are (lighter/heavier) than water

Answer 19

lighter

Question 20

Substances with a specific gravity >1 are (lighter/heavier) than water

Answer 20

heavier

Question 20

What is the specific gravity of 150mL of glycerin weighing 165g?

Answer 20

SG = 165g/150mL = 1.1

Question 21

Specific Gravity (SG) formula

Answer 21

SG = g/mL

Question 22

Q1C1 formula

Answer 22

Q1 x C1 = Q2 x C2
Q1 = old quantity
C1 = old conc
Q2 = new quantity
C2 = new conc

Question 23

Alligation example question
Prepare 80g of a 12.5% ichthammol ointment with 16% and 12% ichthammol ointments. How many grams of each?

Answer 23

16% - 12.5% = 3.5 parts of lower conc (12%)
12% - 12.5% = 0.5 parts of higher conc (16%)
80g/ 4 parts = 20g per part
0.5 parts of 16% = 10g of 16%
3.5 parts of 12% = 70g of 12%

Question 24

Alligation example question
Prepare 1% morphine sulfate oral solution. 120mL bottle of morphine sulfate labeled 20mg/5mL and a 240mL bottle of morphine sulfate labeled 100mg/5mL
How much of 100mg/5mL should be added to the 20mg/5mL bottle?

Answer 24

20mg/5mL = 0.4%
100mg/5mL = 2%
2%-1% = 1 part of lower conc (0.4%)
0.4-1% = 0.6 part of lower conc (2%)

120mL of 20mg/5mL bottle (0.4%) = 1 part
0.6 part of 120mL = 72mL of higher conc (2%)

Question 25

___ is the measure of total # of particles (or solutes) per L of solution

Answer 25

Osmolarity (Osmol/L or mOsmol/L)

Question 26

Osmolarity will always need to be normalized to a volume of ___

Answer 26

1L

Question 27

mOsmol/L Formula

Answer 27

mOsmol/L = (Wt of substance (g/L)) / (MW (g/mol)) * (# of particles) * 1000
1. Add up the # of particles when compound dissociates
2. Calculate $ of grams of compound present in 1 L
3. Use MW to solve problem

Note: milliosomole calculations do not normalize to 1 liter

Question 28

Dissociation factor (i) based on number of dissociated ions

Answer 28

i = 1 + 0.8 (for each additional dissociated ion)
Example
4 dissociated ions = 1 + (0.8*3) // i = 3.4

Question 29

Sodium chloride equivalent or “E value” formula

Answer 29

E = (58.5)(i) / (MW of drug)(1.8)

Question 30

Calculate E value for mannitol (MW=182g/mol)

Answer 30

58.5(1) / 182(1.8) = 0.18

Question 31

T/F: For monovalent species, the numeric value of the milliequivalent and millimole are identical

Answer 31

True

Question 32

mEQ formula

Answer 32

mEq = mg*valence / MW