Percentage and Ratio Strength Calculations

PercentagePercent weight-in-volume (w/v): The number of grams of a constituent in 100 ml of solution or liquid preparation.-The term used for solutions or suspensions of solids in liquids.

Percent volume-in-volume (v/v): The number of ml of a constituent in 100 ml of solution or liquid preparation.The term used for solutions of liquids in liquids.

Percent weight-in-weight (w/w): The number of grams of a constituent in 100 g of solution or mixture.-The term used for mixtures of solids and semisolids.

The term milligrams percent (mg%): The number of milligrams of a substance in 100 ml of liquid.The term used to denote the concentration of a drug or natural substance in a biological fluid, as in the blood.

Percentage and ratio strength (Cont.)Parts per million (ppm): The term used for very dilute solutions. It is used to designate test limits. e.g.the limit of arsenic in zinc oxide is 6 ppm.Examples

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

5 % w/v means : 5 gm 100 ml X gm 4000 ml

X = 200 gm

Percentage and ratio strength (Cont.)2- A sunscreen lotion contains 5 % (v/v) of menthyl salicylate. How many milliliters of menthyl salicylate should be used in preparing 5 pt of the lotion ??Answer 5 pt = 5 x 16 f-oz x 30 ml = 2400 ml 5 ml 100 ml lotion X ml 2400 ml X = 120 ml

Percentage and ratio strength (Cont.)3- If 1500 g of a solution contain 75 g of a drug substance, what is the percentage strength (w/w) of the solution ??

Answer75 g of drug 1500 gX g 100 g% = 75 x 100 / 1500 = 5 % w/w