University of Kerbala College of Pharmacy Department of Pharmaceutics Principles of Pharmacy Practice Lecture 3 PERCENTAGE and RATIO STRENGTH Assistant lecturer Zahraa Alaa Hasan MSc. Drug Delivery 2018-2019
Objectives To define the expressions percent weight-in-volume, percent volume-in -volume, and percent weight-in - weight. To define the expression ratio strength. To convert percent strength to ratio strength and vice versa. To calculate the percentage strength and ratio strength of pharmaceutical preparations. 2
Percentage The concentration of a solution may be expressed in terms of the quantity of solute per definite volume of solution or as the quantity of solute per definite weight of solution. The quantity (or amount) is an absolute value (e.g., 10 ml, 5 g, etc.), whereas concentration is the quantity of a substance in relation to a definite volume or weight of other substance (e.g., 2g/2mL, 2mL/5mL, 2g/5g, etc.). The percentage concentrations of active and inactive constituents in various types of pharmaceutical preparations are defined as follows by the United States Pharmacopeia: 3
Percentage Concentration Expressions Percent weight-in-volume: expresses the number of grams of a constituent in 100 ml of solution (it is used regardless of whether water or another liquid is the solvent). It expressed by the following symbol: (%w/v) Percent volume-in-volume: expresses the number of milliliters of a constituent in 100 ml of solution. Expressed as: (%v/v) Percent weight-in-weight: expresses the number of grams of a constituent in 100 g of a preparation. Expressed as: (%w/w) 4
Cont. Percentage Concentration Expressions In general, the nature of the ingredients in a pharmaceutical preparation determines the basis of the calculation. Therefore, when the term percent, or the symbol %, is used without determination of its type, the appropriate assumption must be made as below: For solutions or suspensions of solids in liquids, percent weight-in-volume. For solutions of liquids in liquids (emulsions), percent volume-in-volume. For mixtures of solids or semisolids (ointments, creams, and gels), percent weight-in-weight 5
Cont. Percentage Concentration Expressions In most instances, the use of percentage concentrations in the manufacture and labeling of pharmaceutical preparations is restricted to instances in which the dose of the active ingredient is not specific. For example, the active ingredients in ointments, creams and lotions may commonly be expressed in percent strength (e.g., 1% hydrocortisone ointment). 6
Cont. Percentage Concentration Expressions However, in most dosage forms, such as tablets, capsules, injections and syrups, the amounts of active ingredients are expressed in definitive units of measure, such as milligrams per capsule, milligrams per milliliter in syrups, or other terms. Additionally, many pharmaceutical formulations or pharmaceutical components such as flavoring agents, solvents, preservatives, and so on, may be expressed in terms of their percentage concentration. 7
Examples of Weight-in-Volume Calculations Example1: How many grams of dextrose are required to prepare 4000 ml of a 5% solution? Answer: 5 g 100 ml = X g 4000 ml X = 200 g. Example2: How many grams of aminobenzoic acid should be used in preparing 236.5 ml of a 5% solution in 70% alcohol? Answer: 5 g 100 ml = X g 236.5 ml X = 11.83 g. 8
Examples of Weight-in-Volume Calculations Example3: How many grams of potassium permanganate should be used in compounding the following prescription? Rx Potassium Permanganate 0.02% Purified Water ad 250 ml Sig. as directed. Answer: 0.02 g 100 ml = X g 250 ml X = 0.05 g. 9
Examples of Weight-in-Volume Calculations Example4: What is the percentage strength (w/v) of a solution of urea, if 80 ml contains 12 g? Answer: Percentage = part total 100 % 12 g = * 100 80 ml = 15 % w/v. 10
Examples of Volume-in-Volume Calculations Example5: How many milliliters of liquefied phenol should be used in compounding the following prescription? Rx Liquefied Phenol 2.5% Calamine Lotion ad 240 ml Sig. For external use. Answer: 2.5 ml 100 ml = X ml 240 ml X = 6 ml 11
Examples of Volume-in-Volume Calculations Example6: Peppermint spirit contains 10% v/v of peppermint oil. What volume of the spirit will contain 75 ml of peppermint oil? Answer: 10 ml 100 ml = 75 ml X ml X = 750 ml Example7: In preparing 250 ml of a certain lotion, a pharmacist used 4 ml of liquefied phenol. What was the percentage (v/v) of liquefied phenol in the lotion? Answer: Percentage = part total 100 % = 4 ml 250 ml * 100 = 1.6 % (v/v) 12
Examples of Weight-in-Weight Calculations Example8: How many grams of phenol should be used to prepare 240 g of a 5% (w/w) solution in water? Answer: 5 g = X g 100 g 240 g X = 12 g 13
Examples of Weight-in-Weight Calculations Example9: 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? Answer: Weight = volume * Sp. gr. Weight = 120 x 1.15 = 138 g 20 g = X g 100 g 138 g X = 27.6 g 14
Examples of Weight-in-Weight Calculations Example10: If 5 g of boric acid is added to 100 ml of water, what is the percentage strength (w/w) of the solution? Answer: (100 ml water = 100 g) Since 5 g is added to water, then: 5 + 100 = 105 g (total weight). Percentage = part total 100 % = 5 105 * 100 % = 4.76 % (w/w) 15
Ratio Strength A ratio indicates a relation or comparison of two like quantities. The concentrations of weak solutions are frequently expressed in terms of ratio strength. For example, 5% means 5 parts per 100 or 5:100. Ratios having the same values are equivalent. Ex: 4:5 = 12:15 : 16
Ratio strength practice Example1: Express 0.02% as a ratio strength. 0.02 % 100 % = 1 part X parts Ratio strength 1:5000 X= 5000 (Do not forget the colons) Example2: Express 1:4000 as a percentage strength. 1 part = X % 4000 parts 100 % X= 0.025% 17
Ratio strength practice Example3: How many grams of potassium permanganate should be used in preparing 500 ml of a 1:2500 solution? 1 g 2500 ml X= 0.2 g = X g 500 ml Example4: How many milligrams of 1:10,000 gentian violet should be used in preparing 500 ml solution? 1 g 10 000 ml = X g 500 ml X= 0.050 g * 1000 = 50 mg 18
Example5: How many milligrams of hexachlorophene should be used in compounding the following prescription? Rx Ratio strength practice Hexachlorophene 1:400 Hydrophilic Ointment Sig. Apply. Answer: 1 g = X g 400 g 10 g X= 0.025 g * 1000 = 25 mg ad 10 g 19
Learning outcomes Percentage strength and ratio strength were defined. Mathematically, percent strength was converted to ratio strength and ratio strength to percent strength. The percentage strength and ratio strength of pharmaceutical preparations were calculated successfully following the application of the learnt methods. 20
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