Compounding Corner – February 2017
Preparation of a Magistral Formulation

You receive a prescription in your pharmacy with the following details:

Patient’s name : Rose D
Age : 50
Sex: F

Prescription: External solution

Direction: Apply on the wart
Salicylic acid 8g
Lactic acid 8g
Alcohol 90% v/v qs dissolve
Collodion to 50g



1. What is the difference between a solution and a suspension?
2. What is the use of alcohol 90% v/v in this formulation?
3. You are asked to prepare this external solution. What should you check first?
4. How much alcohol 90% v/v (in grams) would be required to produce the 50g solution?
5. You have bottles of 30 ml, 60 ml, and 90 ml available in your pharmacy. Which size of bottle are you going to use and explain your choice?
6. Salicylic and lactic acids are active ingredients. What are their properties on the skin?
7. What is the use of collodion in this preparation?
8. Indicate two organoleptic properties of alcohol 90% v/v.
9. Alcohol is an excipient. Give the definition of an excipient.
10. What are the labelling considerations for this preparation?


Here are some indications to answer the questions:

– one gram of salicylic acid is dissolved in 2.2 mL of alcohol 90% v/v
– density of the solution: 0.89 g/ml
– density of alcohol 90% v/v: 0.83 g/ml
– note: density=mass/volume