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Question

Posted on: March 6 2013

Calculations in the preparation of benzoyl peroxide and erythromycin TMF.

I had a further training yesterday due to TMF but I have problems with the calculations, which should be performed in the preparation of benzoyl peroxide and erythromycin TMF. According to the instructor, due to the instability of the products, 10% more should be weighed, a water content of 25% should be taken into account in benzoyl peroxide and all constituents should be weighed 10% more for the loss in the Ointment Grinder. For example, I find that for 50g ointment 1, 815g erythromycin should be weighed; According to the TMF and the teacher, this is 1, 98g. For benzoyl peroxide I find 3, 66g while the TMF and the instructor specify 4, 03g.
can you explain my difference please?

Answer

A. erythromycin (concentration = 3%)

  1. we foresee a loss of 10% by treatment with ointment grinder so we prepare 55g ointment instead of 50g
  2. for 55 g We need 55 X 0.03 = 1.65 erythromycin
  3. we foresee a breakdown and carry an overdose of 20% so 1.65 X 1.2 = 1, 98g haemoglobin.

B. Benzoyl peroxide (concentration = 5%)

  1. correction for water content of 25% gives 5/0.75
  2. also another correction of 10% for degradation (5/0.75) x 1.1 = 7.333%
  3. for 55 g = 4, 03g BzPO