I was after some help with figuring out what calculation to use when determine the MACO for topical products... I am trying to determine the surface limit (mg/100cm2) for 0.1% of the normal therapeutic dose of any product appearing in the maximum daily dose of the following product. I have 2 formulas but am not sure which one to use as they give different results...
First formula =
(0.1% x lowest therapeutic dose (A) x batch size (B) x swab area) / (maximum daily dose (B) x total equipment surface area)
Second forumla =
(0.1% x lowest available strenth of API in the product A (%) x batch size (B) x swab area) / (total equipment surface area)
The first formula is in terms of dosages (eg. 0.025g therapeutic dose) where as the second formula is in terms of the overall strength of API in the batch of A (eg. 5% API).
I have seen both formulas used before but am not clear on which one is the correct way to determine the 0.1% carry over limit.
If anyone could shed some light on this it would be great.