Hi there!
I have a question that came up during the development of the test method for N‑Nitroso Desmethyl Terbinafine.
For tablet formulations, the acceptable daily intake is clearly defined (for example, one time one tablet and two times per day).
However, for ointments or topical solutions, the daily usage amount is not clearly defined.(for example, Depending on the indication, it is applied once or twice daily)
I would appreciate your thoughts on what would be a reasonable approach to clearly determining the daily usage amount in milliliters or grams.
The cosmetics industry has guidelines around leave on creams and the total weight of product used. It may be worthwhile investigating those. I think there are some for full body and then some specific for face etc. From those you will then need to estimate a relative amount of the body that your consumer/patient is likely to cover with the product to estimate a total daily amount used, taking into account the number of applications per day.
It isn’t an exact science, compared to tablets, you need to be able to justify your calculations both internally and to potential authorities and assessors.
Terbinafine cream (typically 1%) is an antifungal medication used to treat common skin infections, including athlete’s foot (tinea pedis), jock itch (tinea cruris), ringworm (tinea corporis), and tinea versicolor. It kills fungi by destroying their cell membranes, relieving itching, cracking, and burning.
There is a way to calculate exposure. In pharma tox, we call it Finger Tip Unit, and cosmetics it is called as face cream application; however sicne it is an API and not a cosmetic or personal care ingredient, I would be using FTU, which is a standard across all industry for topical application (steroids and anti-microbials).