Reducing and enlarging formulas

1. Reducing and enlarging formulas Dr. Osama A. A. Ahmed

2. Reducing and enlarging formulas • Factor (F) = Amount desired/ amount of formula • From the following formula, calculate the quantity of each ingredient required to make 240 ml of calamine lotion: • Calamine 80 g • Zinc Oxide 80 g • Glycerin 20 ml • Bentonite magma 250 ml • Lime water (Calcium Hydroxide) to 1000 ml • Factor (F) = 240/1000 = 0.24 • X 0.24 • Calamine 80 g 19.2 g • Zinc Oxide 80 g 19.2 g • Glycerin 20 ml 4.8 ml • Bentonite magma 250 ml 60 ml • Lime water to 1000 ml to make 240 ml Dr. Osama A. A. Ahmed

3. Dilution, Concentration and Alligation • Factor (F) = Amount desired/ amount of formula • From the following formula, calculate the quantity of each ingredient required to make 1000 g of the ointment : • Coal tar 5 parts • Zinc Oxide 10 parts • Hydrophilic ointment 50 parts • Total number of parts = 65 • 1000 g will contain 65 parts • Factor (F) = 1000/65 = • X 1000/65 • Coal tar 5 parts 76.92 g • Zinc Oxide 10 parts 153.85 g • Hydrophilic ointment 50 parts 769.23 g Dr. Osama A. A. Ahmed

4. Selected calculation in contemporary compounding • Constitution of dry powders for oral solution or suspension • Some drugs as antibiotics lose their potency in a relatively short period when prepared in a liquid dosage form. • Example: the label of dry powder package of cefprozil (CEFZIL) for oral suspension directs the pharmacist to add 72 ml of purified water to prepare 100 ml of suspension. If the package contains 2.5 g of cefprozil, how many milligrams of the drug would be contained in each teaspoonful dose of the constituted suspension? • 2.5 g = 2500 mg • 2500 mg 100 ml • X mg 5ml X = 125 mg cefprozil Dr. Osama A. A. Ahmed

5. Selected calculation in contemporary compounding • Example: the label of a dry powder for oral suspension states that when 111 ml of water are added to the powder, 150 ml of a suspension containing 250 mg of ampicillin per 5 ml are prepared. How many milliliters of purified water should be used to prepare, in each 5 ml of product, the correct dose of ampicillin for a 60-lb. child based on the dose of 8 mg/kg of body weight? • 1 kg 2.2 lb • X kg 60 lb X = 60/2.2 = 27.273 kg • ampicillin dose = 27.273 X 8 = 218 mg • Total amount of ampicillin in the container • 250 mg 5 ml • X mg 150 ml X = 7500 mg • The new volume to be prepared • 218 mg 5 ml • 7500 mg X ml X = 172 ml • As the dry powder occupies 39 ml (150 ml – 111 ml ), so the amount of water added is • Amount of water = 172 – 39 ml = 133 ml Dr. Osama A. A. Ahmed

6. Selected calculation in contemporary compounding • Constitution of dry powders for parenteral solution • Example: Using a vial containing 200,000 units of penicillin G potassium, how many milliliters of solvent should be added to the dry powder in preparing a solution having a concentration of 25,000 units/ ml? • 25,000 units 1 ml • 200,000 units X ml X = 8 ml • Use of prefabricated dosage forms in compounding • Example: Only capsules, each containing 25 mg of indomethacin, are available. How many capsules should be used to obtain the amount of indomethacin needed in preparing the following prescription? • R/ Indomethacin 2 mg/ml • Cherry syrup ad 150 ml • Sig. 5 ml b.i.d • Amount of indomethacin needed in the prescription = 150 X 2 = 300 mg • 1 capsule 25 mg • X capsules 300 mg X = 12 capsules needed Dr. Osama A. A. Ahmed