Yewande Dayo Student Pharmacist Objectives Define percent weightinvolume percent volumeinvolume and percent weightinweight Define ratio strength Convert percent strength to ratio strength and ratio strength to percent strength ID: 549677
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Slide1
Percentage, Ratio Strength, and Other Expressions of Concentration
Yewande Dayo
Student PharmacistSlide2
Objectives
Define percent weight-in-volume, percent volume-in-volume, and percent weight-in-weight.
Define ratio strength.
Convert percent strength to ratio strength and ratio strength to percent strength.
Calculate the percent strength and ratio strength of a pharmaceutical preparation.
Apply percent strength and ratio strength to calculate the quantity of an ingredient present in a pharmaceutical preparation.
Apply percent strength and ratio strength to calculate the quantity of an ingredient to use in compounding a pharmaceutical preparation.Slide3
Percentage Strength
Percentage strength and its corresponding sign (%) means rate per hundred
50% = 50 parts in 100 = 0.50
The pharmacist usually encounters liquid preparations where the parts represent grams of ingredient in 100
mL
of liquid preparation.Slide4
Percentage Preparations
Percent Weight in Volume (
w/v
): number of grams in 100mL of solution. Expressed as: ______%
w/v
Percent Volume in Volume (
v/v
): number of milliliters in 100
mL
of solution. Expressed as: ______%
v/v
Percent weight in weight (
w/w
): number of grams in 100 grams of solution. Expressed as: ______%
w/w
Slide5
Assumptions
If the term % is used without qualification the following are assumed
:
mixtures of solids and semisolids (%
w/w
)
solutions or suspensions of solid in liquid (%
w/v
)
solutions of liquid in liquid (%
v/v
)Slide6
Example 1
How many milligrams of ephedrine sulfate should be used in preparing the following prescription
?
R
x
Sol. Ephedrine Sulfate ½% 30
mL
Sig. For the noseSlide7
Example 2
How many milligrams of certified red color should be used in preparing 5 liters of a 0.01% solution?Slide8
Example 3
If a pharmacist dissolves the contents of eight capsules containing 250 mg
clindamycin
HCl
per capsule into sufficient amount of astringent liquid to prepare 120
mL
of solution, what is the percentage strength (
w/v
) of
clindamycin
HCl
in the prescription? Slide9
Example 4
If 425
g
of sucrose
is
dissolved in enough water to make 500
mL
, what is the percentage strength of the solution?Slide10
Example 5
A sunscreen lotion contains 5% (
v/v
) of
methyl
salicylate
. How many milliliters of
methyl
salicylate
should be used in preparing 5 pints of the lotion?Slide11
Example 6
What is the percentage strength (
v/v
) if 225
g
of a liquid having a specific gravity of 0.8 are added to enough water to make 1.5 liters of the solution?Slide12
Example 7
How many grams of a drug substance should be dissolved in 1800
mL
of water to make a 10% (
w/w
) solution?Slide13
Example 8
How many grams of potassium permanganate should be used in compounding the following prescription
Rx
Potassium Permanganate 0.02%
Purified water ad 250
mLSlide14
Example 9
If 500
g
of dextrose are dissolved in 600
mL
of water with a resultant final volume of 1 liter, what is the percentage strength of dextrose in the solution on a
w/w
basis?Slide15
Example 10
One pound of fungicidal ointment contains 9.08
g
of
undecylenic
acid. Calculate the percentage
w/w
of
undecylenic
acid in the ointment.Slide16
Final volume in w/w
It is usually impossible to prepare a final specific volume of %
w/w
solution because the volume displaced by the active drug cannot be known in advance. Slide17
Example 11
How
w
ould
you prepare 100
mL
of a 2% (
w/w
) solution of a drug substance in a solvent having a specific gravity of 1.25?Slide18
Example 12
If 1500
mL
of a solvent with a specific gravity 0.85 are used to dissolve 75
g
of a drug substance, what is the percentage strength (
w/w
) of the solution?Slide19
Example 13
If 5
g
of boric acid
is
dissolved in 100
mL
of water, what is the percentage strength (
w/w
) of the solution?Slide20
Example 14
If 1000
mL
of syrup with a specific gravity of 1.313
contains
850
g
of sucrose, what is its percentage strength (
w/w
)?Slide21
Example 15
What weight of a 5% (
w/w
) solution can be prepared from 2
g
of active ingredient?Slide22
Ratio Strength
Solids in liquids = 1:1000 = 1
g
in 1000
mL
of solution
Liquids in liquids = 1:1000 = 1
mL
in 1000
mL
of solution.
Solids in solids = 1:1000 = 1
g
in 1000
g
of mixture.Slide23
Example 16
Express 0.02% as a ratio strength and 1:4000 as percentage strength.Slide24
Example 17
How many mg of gentian violet should be used in preparing the following solution?
R
x
Gentian violet solution 500
mL
1:10,000
Sig. Instill as directedSlide25
Example 18
How many mg of hexachlorophene should be used in compounding the following prescription?
R
x
Hexachlorophene 1:400
Hydrophilic
Oint
. ad 10
g
Sig. Apply.Slide26
Conversion to mg/mL
Convert 4% (
w/v
) to mg/
mLSlide27
Example 19
Convert 1:10,000 (
w/v
) to mg/
mL
Convert a product concentration of 1g per 250
mL
to mg/
mLSlide28
Parts per Million (PPM)
1 part of solute per 1 million part of the solution, e.g., 1:1,000,000Slide29
Example 20
Express 5
ppm
of iron in water in percent strength and ratio strength.Slide30
Problem 21
R
x
Gentamicin
(40 mg/
mL
) Inj. 2
mL
Gentamicin
(0.3%)
Oph
. Soln. 5
mL
Calculate the percent concentration of
gentamicin
in this
fortified ophthalmic solution.Slide31
Problem 22
Mellaril
-S Suspension contains 25 mg of
thioridazine
per 5
mL
of suspension. What is the percentage strength (
w/v
) of
thioridazine
in the suspension?Slide32
Rx
Ofloxacin
Opthalmic
Solution 0.3%
Disp
10
mL
Sig: 2 drops into eyes
q
4 hours
x
2days; then 2 drops
q
6 hours
x
4 days
How many grams of
Ofloxacin
should be used in preparing the prescription