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 ≈ ml
X gm ≈ ml
X = 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 = ml
5 ml ≈ ml lotion
X ml ≈ 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 ≈ g
X g ≈ g
% = 75 x 100 / = 5 % w/w