PERCENTAGE PREPARATIONS

Dr. Amani M. Elsayed

Objectives

• Solve pharmaceutical calculation problems involving percentage strengths

PERCENTAGE PREPARATIONS

•Percentage means “by the hundred” or “in a hundred.” Percents (%) are just fractions, but fractions with a set denominator of 100.– Example: “50%” means “50 in a hundred” or

“50/100” or “1/2”.•Converting percentages to fractions– Write the number preceding the percent sign over

100 and simplify the resulting fraction– Example: 25%=25/100=1/4

PERCENTAGE PREPARATIONS

• Converting fractions to percentages1. Write the fraction in decimal form. (3/4=0.75)2.Write the decimal over one. (0.75/1)3.Multiply the numerator and denominator by 100.

(0.75/1 = 75/100)4.Because you already know the “divided by a

hundred” is the same as percent you can write 75/100 as 75%.

TYPES OF PERCENT

• a. W/W percent or Weight/Weight percent is defined as the number of grams in 100 grams of a solid preparation.

• • (1) Example #1 A 5 percent (w/w) boric acid

ointment would contain 5 grams of boric acid in each 100 grams of boric acid ointment.

• (2) Example #2:A 3 percent (w/w) vioform powder would contain 3grams of vioform in every 100 grams of the vioform powder.

TYPES OF PERCENT

• b. W/V of Weight/Volume percent is defined as the number of grams in 100 milliliters of solution.

• • (1) Example #1:A 10 percent (w/v) potassium

chloride (KCL) elixir would contain 10 grams of potassium chloride in every 100 milliliters of KC1 elixir.

• •

TYPES OF PERCENT

• c. V/V percent or Volume/Volume percent is defined as the number of milliliters in every 100 ml of solution.

• • (1) Example #1:A 70% (v/v) alcoholic solution would

contain 70 milliliters of alcohol in every 100 ml of solution.• • (2) Example #2:A 0.5% (v/v) glacial acetic acid solution

would contain 0.5 milliliters of glacial acetic acid in each 100 milliliters of solution.

•

Examples

1) How many grams of dextrose are required to prepare 4000 ml of a 5% solution?

2)How many grams of potassium permanganate should be used in compounding the following prescription?

℞ Potassium permanganate 0.02% Purified water ad 250 ml Sig. As directed

Answers

1) 5g 100 ml X g 4000 ml X = 5 * 4000 = 200 g 100 2) 0.02 g 100 ml X g 250 ml X = 0.02* 250 = 0.05 g 100

Examples

3) How many grams of aminobenzoic acid should be used in preparing 8 fluidounces of a 5% solution in 70% alcohol?

4) What is the percentage strength (w/v) of a

solution of urea, if 80 ml contain 12 g?

Answers

3) 8 fluidounces = 8 * 30 = 240 ml 5 g 100 ml X g 240 ml X = 5* 240 = 12 1004) 12 g 80 ml X g 100 ml X = 12* 100 = 15% 80

Examples

5) How many milliliters of a 3% solution can be made from 27 g of ephedrine sulfate?

6) How many milliliters of liquified phenol should be used in compounding the following prescription?

• ℞ Liquified phenol 2.5% Calamine lotion ad 240 ml Sig. For external use

Answers

5) 3 g 100 ml 27 g X ml X = 27* 100 = 900 ml 36) 2.5 ml 100 ml X ml 240 ml X = 2.5* 240 = 6 ml 100

Examples

7) In preparing 250 ml of a certain lotion, a pharmacist used 4 ml of liquified phenol. What was the percentage (v/v) of liquified phenol in the lotion?

8) Peppermint spirit contains 10% (v/v) of peppermint oil. What volume of the spirit will contain 75 ml of peppermint oil?

Answers

7) 4 ml 250 ml X ml 100 ml X = 4* 100 = 1.6% 2508) 10 ml 100 ml 75 ml X ml X = 75* 100 = 750 ml 10

Examples

9) What is the percentage strength (v/v) of a solution of 800 g of a liquid with specific gravity of 0.800 in enough water to make 4000 ml?

10) How many grams of phenol should be used to prepare 240 g of a 5% w/w solution in water?

Answers9) Weight/ sp.gr = Volume 800/ 0.800 = 1000 ml 1000 ml 4000 ml X ml 100 ml X = 1000* 100 = 25% 400010) 5 g 100 g X g 240 g X = 5* 240 = 12 g 100

Examples

11) How many grams of a drug substance are required to make 120 ml of a 20% (w/w) solution having a specific gravity of 1.15?

12) How many grams of a drug substance should be added to 240 ml of water to make a 4% (w/w) solution?

Answers11) Weight of solution = sp. gr. * Volume = 1.15 * 120 = 138 g 20 g 100 g X g 138 g X = 20* 138 = 27.6 g 10012) Weight of water = weight of solution- weight of drug = 100 g – 4 g = 96 g Weight of water = volume * Density = 240 * 1 = 240 g 4 g 96 g of water X g 240 g of water X = 4* 240 = 10 g 96

Bonus Questions

1) If 5 g of boric acid are added to 100 ml of water, what is the percentage strength (w/w) of the solution?

2) How many milligrams of hydrocortisone should be used in compounding the following prescription?

℞ Hydrocortisone 1/8 % Hydrophilic ointment ad 10 g Sig. Apply

Bonus Questions

3) How many grams of benzocaine should be used in compounding the following prescription?

℞ Benzocaine 2% Polyethylene Glycol base ad 2 g Make 24 such suppositories Sig. Insert one as directed

Bonus Questions

4) If ibuprofen tablets are permitted to contain not less than 90% and not more than 110% of the labeled amount of ibuprofen, what would be the permissible range in content of the drug, expressed in milligrams, for ibuprofen tablets labeled 200 mg each?

Homework

1) If 1500 g of a solution contain 75 g of a drug substance, what is the percentage strength (w/w) of the solution?

2) If 1000 ml of a syrup with a specific gravity of 1.313 contain 850 g of sucrose, what is the percentage strength (w/w)?

3) What weight of a 5% (w/w) solution can be prepared from 2 g of active ingredient?

Homework

4) If a veterinary liniment contain 30% (v/v) of dimethyl sulfoxide, how many milliliters of the liniment can be prepared from 1 lb of dimethylsulfoxide (sp. gr. 1.10)?