Pharmacy Formulation Calculation Question

What is the percentage of Betamethasone Valerate in the following ointment? Liquid Paraffin 50g Emulsifying was 50mg Betamethasone Valerate 400mg Yellow soft paraffin to 200g.

1. 4%
2. 2%
3. 0.2%
4. 0.4%
5. 0.04%

Students working...?

1- 0.1g/100g
    0.4g     x                      = 0.4 x 0.1 / 100 = 400/200 = 2%

Where did you get 0.1g in 100g? It looks like you are using some sort of formula. You need to visualize what this requires. Writing it down often helps. When I attempted this I wrote down all of the ingredients (but you don't need to in the end as it is made up to 200g).

• Step 1: You need to figure how much betamethasone is in the total amount of the mix.The total weight is 200g as at the end it says it is made up to 200g and the amount in this is 400mg.
• Step 2: Convert to similar units ie 400mg is equivalent to 0.4g.
• Step 3: Create a percentage by now you know 0.4g/200g is what you need. This is quiet easy in your head just half it, giving 0.2g/100g which is your answer 0.2% which is 3.

*"Yellow soft paraffin to 200g" - this is a little ambiguously worded, however it remains as the questions in the exam will not be perfect.