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Question

Posted on: December 6 2018

Precipitation in a 0.025% Tretinoin solution

There are oblong crystals in the solution below, although after the preparation everything was nicely dissolved. Formula: 0.025 g tretinoin, 0.2 g Vitamin C, 10 g PG, 44.89 G, Aqua Purificata and 44,885 G Ethanol 96 ° for 100 gram Solution

Answer

You should use following compound: Tretinoin 0.025 g; Butylhydroxytolulene (BHT) 0.055 g; Propylene glycol 50 g and ethanol up to 96 ° to 100 G..  

I see in your composition vitamin C listed. You can use it even though BHT is the appropriate ant-Oxidance for Tretinoin, which is a lipophilic substance.  

This is the composition of the German Formularium. This is anhydrous

You have the advantage to first dissolve the Tretinoin in the largest part ethanol since the solubility of tretinoin in alcohol is much greater as in PG!!

  I do not exclude that when we change your composition A solution is also obtained in which there are no crystals

R: 0.025 g tretinoin, 0.2 g vitamin C,   44.89 g PG, 10 g   Aqua Purificata and 44,885 G Ethanol 96 ° for 100 gram solution