15% Urea cream - Crystals forming in the tube opening

Hi

I developed a 15% urea foot cream 10 days back. Its stable at 40 C 75% RH, and 50 C for now. However, there are crystals formed in the tube orifice.
Need help on resolving this issue. 

Formula: 
LLP 10%
Butters 4%
Herbal extract (coconut oil based) 3% - Provided by client
Cetyl Palmitate 2.5%
Arlacel 165 3.5%
Cetyl alcohol 2.5%

DM Water Qs to 100
Carbopol 940 0.4%
Urea 15%

Preservative Qs
Perfume Qs
Color Qs


Should I be adding something else to stabilise urea? 

Please help!

Comments

  • PharmaPharma Member, Pharmacist
    edited September 2021
    ...
    Should I be adding something else to stabilise urea? 
    ...
    Yes. With 15% urea you should. Adjust pH to around 6.2 (rather lower than higher), use a buffer if possible, and add triethyl citrate or triacetin.
    BTW this only increases shelf life of urea but does not prevent crystal formation. Adding glycerin or another liquid diol/polyol might help with that.
  • The pH by itself is 6.28. So, I left it a such. Should I still do something to increase shelf life?

    I will try adding glycerin or polyols. 

    Thanks for the help :)



  • PharmaPharma Member, Pharmacist
    The issue with urea is that once it starts degrading it increases pH and that in turn accelerates degradation. A chemical vicious cycle. And that's wyh you're on the safer side with some additives which stop the pH from rising.
  • Pharma said:
    ...
    Should I be adding something else to stabilise urea? 
    ...
    Yes. With 15% urea you should. Adjust pH to around 6.2 (rather lower than higher), use a buffer if possible, and add triethyl citrate or triacetin.
    BTW this only increases shelf life of urea but does not prevent crystal formation. Adding glycerin or another liquid diol/polyol might help with that.
    I have a questIon regarding buffers and ph. If I wanted to use a buffer to get say a Urea containing product to a ph of 6.0 should the buffer itself have a ph of 6 or should the buffers ph be lower so as to effectively  reduce the ph of said urea containing product down to say a ph of 6?  
  • PharmaPharma Member, Pharmacist
    The buffer should be bring the product to the aimd at pH (i.e. 6.2ish). However, a good buffer will have its buffering range around pH 6 to 7 (and not, as an example, an upper limit at 6).
  • I'm actually surprised the product is stable at 40 C 75% RH and 50 C. 
  • we have 10% urea in foot cream & is stable.
  • @em88 Yes it is stable. But still there are crystals forming in the tube opening.
    @amitvedakar We re-formulated with 10% urea and its stable. 
  • our is bottle packing
  • @Padmavathi, Well,  what do you mean by stable? 
  • @em88 I meant that there was no separation (probably shouldn't have said stable?).
    We squeeze the tube to get the cream out and close the cap, and open it again the next day to get more cream.. there are crystals in the opening, which come out along with the cream. Just a tiny bit. This did not happen with 5% or 10% urea. 
    Haven't had time to work more on the 15% cream. 
Sign In or Register to comment.