part 5: DENSITY AND SPECIFIC GRAVITY, EXPRESSION AND CALCULATION OF DRUG AMOUNTS

Density

Mass per unit volume of substance (g/mL)

Specific gravity

Ratio of a weight of a substance to a weight of equal volume of standard

0.812 g/mL

If 250 mL of alcohol weighs 203 g, what is its density?

0.86

A pycnometer weighs 21.62 g. Filled with water, it weighs 46.71 g; filled with another liquid, it weighs 43.28 g. Calculate the specific gravity of the liquid.

w/v (%) = mass of solute (g)/volume of solution (mL) x 100

Formula of Percent weight-in-volume (%w/v)

200 g

How many g of dextrose are required to prepare 4000mL of a 5% solution?

15%

What is the percentage strength (w/v) of a solution of urea, if 80mL contain 12 g?

v/v (%) = volume of solute (mL)/volume of solution (mL) x 100

Formula of Percent volume-in-volume (%v/v)

6 mL

How many mL of liquefied phenol should be used in compounding the following prescription?

1. Rx Liquefied Phenol 2.5% (v/v)

a. Calamine Lotion ad 240.0 mL

b. Sig. for external use

1.6% v/v

In preparing 250mL of a certain lotion, a pharmacist used 4mL of liquefied phenol. What was the % v/v of liquefied phenol in the lotion?

w/w (%) = mass of solute (g)/mass of solution (g) x 100

Formula of Percent weight-in-weight (%w/w)

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

• True percentage or percentage by weight

• For mixtures of solids and semi-solids; also for liquid preparation

10 g

How many g of a drug substance should be dissolved in 240mL of water to make a 4% (w/w) solution?

5%

If 1500g of a solution contain 75g of a drug substance, what is the %w/w of the solution?

Ratio

• Relationship of a part to the whole

• Relate a quantity of liquid to a quantity of solution

• Used to calculate dosages of dry medication such as tablets

66.66%

Convert 2:3 to a percent

¼

Convert 25% to a ratio

1/5000

Express 0.02% as a ratio

0.025%

Express 1:4000 as a percentage strength

Parts Per Million (PPM)

• Parts per one million parts

• Used to express concentrations of dilute solutions

• Used to designate test limit

  • Limit of arsenic in zinc oxide is 6ppm or 0.0006%

0.0005%

Express 5ppm of iron in water in % strength and ratio strength

65 mg

The concentration of a drug additive in an animal feed is 12.5 ppm. How many mg of the drug should be used in preparing 5.2 kg of feed?

Parts Per Billion (PPB)

• Parts per one billion parts

• Used to express concentrations of dilute solutions

Proof Strength

• Expressed by taking 50% alcohol or proof spirit as 100 proof

• Always numerically twice as great as percentage strength (v/v)

  • 100% or absolute alcohol is 200 proof

  • 25% alcohol is 50% proof

Proof Gallon

Used to measure or evaluate alcohol of given quantities and strengths for purposed of taxation

1 wine gallon of 100 proof or 50% v/v

Proof Gallons = Wine Gallon x Strength of Solution / 50

Proof Gallon = Wine Gallon x Proof of Strength of Solution / 100 proof

Formulas of Proof Gallon

7.5 proof gallons

How many proof gallons are contained in 5 wine gallons of 75% (v/v) alcohol?

Unit of Potency

Measure of potency for some antibiotics, endocrine products, vitamins

Examples:

Insulin Solution or Suspension

• Most commonly used drug in units

• U-40, U-100, U-500 means 40, 100, 500 USP insulin per mL

Ampicillin Sodium

• 845-998 microgram per milligram

16.67 mg NS

If neomycin sulfate has potency of 60mcg of neomycin per mg, how many mg of neomycin sulfate would be equivalent in potency to 1mg of neomycin?

57.7 g

What is the weight of 60 mL of oil whose density is 0.9624 g/mL?

1:10,000

A vaginal foam contains 0.01% w/v of Dienestrol. Express this concentration as ratio strength.