Percentage and Ratio Strength Calculations

1. Percentage and Ratio Strength Calculations

2. Percentage Percent 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.

3. 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

4. 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

5. 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 ?? Answer 75 g of drug ≈ 1500 g X g ≈ 100 g % = 75 x 100 / 1500 = 5 % w/w