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How to prevent gel evaporating too quickly?
I have made a gel with HEC, but it seems like the water evaporates too quickly and I’m left with white residue on the skin. My goal is transdermal absorption so I think I need to add something to prevent such quick dehydration so it last longer. I’m not sure if white residue is just HEC or my active as well. The formula is this:
5% pentoxifylline
10% propylene glycol
20% transcutol
1% phenoxyethanol/ethylhexylglycerin
Water up to 100%
Any ideas? What am I doing wrong?
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3 Replies
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HEC 2%
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@Creamycreamygel That is a lot of ethoxydiglycol there (Transcutol) which combined with all the propylene glycol may well be reducing the solubility of pentoxyfylline leading to the precipitate. I do not think it can be anything else. You should not need any more than 5.0% ethoxydiglycol to work for skin permeation. You may want to consider reducing the propylene glycol down too. Less is more here.
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@chemicalmatt thank you for your input. I have reviewed quite a few studies and seems like transcutol is most effective at higher concentrations, that’s why I’m using it this way. As for propylene glycol, maybe I should drop it altogether, because pentoxifylline solubility seems pretty low from my experiments.<div>
Solubility in transcutol seems to be the same as in water, around 50-60mg/ml.
I think I will probably have to move to an emulsion with oleic acid, because that would likely be much more effective than a gel anyways and maybe would prevent this problem altogether. It’s just that I’m not yet sure where to order a small amount of Lubrizol Pemulen TR-1 or TR-2.. since that seems like the easiest way for a DIY project with limited equipment.
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