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Is surfactant necessary for my formulation?
Hello everyone. Could anyone tell me if surfactant is necessary for a transdermal formulation that includes 10% oleic acid, 20% transcutol, 10% ethanol, 2% hydroxyethylcellulose, the rest is water.
I plan to use phenoxyethanol/EHG as preservative.
Active ingredient is 5% pentoxifylline. This combination (oleic acid and transcutol) was successfully used in a study with caffeine, but there was no mention of a surfactant. Is Transcutol enough to hold oleic acid in suspension?
Any other advice?
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9 Replies
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Nope! Transcutol (ethoxydiglycol) is there as a glycol ether penetrating agent, also a nifty solvent, but has no surfactant properties. You will need either an alkali hydroxide to combine with all that oleic acid to form a soap or get rid of it altogether. Ethoxydiglycol is a nifty solvent as stated before plus the ethanol should help. Add a little water-soluble acid (lactic acid) to aid solvation with all those amino groups. This may not be creamy but will be a jelly.
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Hi, thank you very much for replying. Any reason not to use something like polysorbate 80?
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Polysorbate 80 is more often used for solubilizing when you have a low percentage of oil (~<1%). To try and use it with 10% of a fatty acid, I imagine you would need to use quite a bit (the general recommendation is 3-4x the oil level) and it will feel sticky/unpleasant. I’d stick with a more traditional emulsifier (but then you might have to move to hot process), or maybe replace HEC with a polymeric emulsifier (I don’t know if your active would cause any problems with one of those)
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Thank you, that’s very helpful. Could you give a few examples of emulsifiers that I could consider, both polymeric and more traditional?
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Traditional: depends on your preference but some of the classics are PEG-100 Stearate & Glyceryl Stearate combo (trade name Arlacel 165, amongst others), or Cetearyl Alcohol & Polysorbate 60 (Emulsifying wax). If ethoxylates are undesirable some other popular options are from the montanov series from Seppic (ex Montanov 68 Cetearyl Alcohol & Cetearyl Glucoside)
Polymeric: something from the Pemulen series from Lubrizol (Acrylates/ C10-30 Alkyl Acrylate Crosspolymer). The also have a more ‘natural’ oriented Pemupur Start, though I haven’t used it myself.
Some combinations are more or less preferred depending on the final desired appearance/feel of the product, availability, cost, etc. There are plenty of threads in this forum that also mention some popular choices. @chemicalmatt is an industry vet, you can also go the route he suggested and saponify.
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Thank you! I will consider my options! Is there a way to get a consultation (for a fee) from some of you guys in case I need more help?
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You can check out some of the contacts here:
chemistscorner.com
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It seems that saponification isn’t really used that often in transdermal preparations? I wonder why?
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@evchem2 do you think carbopol 940 would also work in this scenario? I’m also thinking about potentially replacing oleic acid with isopropyl myristate, but not necessarily.
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