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 g
Zinc Oxide g
Glycerin ml
Bentonite magma ml
Lime water (Calcium Hydroxide) to ml
Factor (F) = 240/1000 = 0.24 X
Calamine g g
Zinc Oxide g g
Glycerin ml ml
Bentonite magma ml ml
Lime water to 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 parts
Zinc Oxide parts
Hydrophilic ointment parts
Total number of parts = 65
1000 g will contain 65 parts
Factor (F) = 1000/65 =
X 1000/65
Coal tar parts g
Zinc Oxide parts g
Hydrophilic ointment parts 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 ml
X mg ml 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 lb
X kg lb X = 60/2.2 = kg
ampicillin dose = X 8 = 218 mg
Total amount of ampicillin in the container
250 mg ml
X mg ml X = 7500 mg
The new volume to be prepared
218 mg 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 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 mg/ml
Cherry syrup ad ml
Sig. 5 ml b.i.d
Amount of indomethacin needed in the prescription = 150 X 2 = 300 mg
1 capsule mg
X capsules mg X = 12 capsules needed
Dr. Osama A. A. Ahmed