Skin Cream with Lidocaine HCl

Anyone familiar with any parameters/interactions with formulating with lidocaine HCl or Lidocaine (base)?

Had a couple trials with lidocaine HCl and the cream developed minute grains.  Typical non-ionic emulsifiers used with xanthan.  pH~7.

Thank you

Comments

  • MicroformulationMicroformulation Member, Professional Chemist
    I have made this product but it most definitely is an OTC product.
    markfuller@microformulation.com Microformulation.com Microformulation Cosmetic Consulting provides Custom Formulations for both large Commercial accounts as well as smaller entrepreneurs. We can provide Naturally compliant Formulations under the NSF, NPA, Whole Foods and USDA Organic Certifications. BS.Pharm Albany College of Pharmacy, Union University.
  • @chickenskin ;I've used either Ultrez 30, Ultrez 20 or Pemulen TR-2 NF with the lidocaine HCL.  Also paired with simugel NS or simugel FL.  I used salonpas lidocaine products as a reference
  • chemicalmattchemicalmatt Member, Professional Chemist
    What Mark Fuller said...OTC Land here you come. The lidocaine base is only for lipid-based formulations or emulsions with high oil loads like the tattoo pain-relief applications. If you have a high oil load in there, switch out to the free base. 
  • Thank you for the comments.  I know this is OTC, I am familiar with the monograph.  I am trying to find the cause of the tiny grains 'barely visible' that form over time (2 days).  Anyone ever see this?  I am thinking it's a preservative interaction.  
  • PharmaPharma Member, Pharmacist
    Lidocain HCl is poorly penetrating skin and that's why the free base is usually used for topical applications (except for wounds and on mucosa).
    Solubility of lidocaine HCl is very good, there shouldn't be any grains forming unless you have a very small water phase, have incompatibilities, or it's something else which causes the issue.
    Mind, neutral pH will result in partial deprotonation of licodain HCl resulting in poorly soluble free base (which is often applied as suspension or else requires solubilisers, solvents, or eutectics).
  • Anyone familiar with any parameters/interactions with formulating with lidocaine HCl or Lidocaine (base)?

    Had a couple trials with lidocaine HCl and the cream developed minute grains.  Typical non-ionic emulsifiers used with xanthan.  pH~7.

    Thank you
    You have to dissolve the xanthan gum very welll
  • Sometimes, it is the technique of making the emulsion and/or the step you are adding Lidocaine Hcl.  Also, The pH of emulsion (Cream).  Usually for Cream: 5.5 - 6.0 unless you are using Salicylic Acid for Acne Cream or making Hair Conditioner.
    You ca dissolve Lidocaine HCL in D.I water at room temp (try to dissolve it in the least amount of water). Sometimes, You may warm the water to 35C - 40C (for faster dissolution), and dissolve Lidocaine HCL in it, then, add it (post-emulsification) to the emulsion at 40 C and Mixing Speed 500 - 600 RPM.  You need to look at the emulsion at this point, if you see it "grainy", you may homogenize it using Silverson Homogenizer at 5000 rpm for 3 min. at the same temp. (40C)
    Also, the thickener you are using and its concentration can be a reason for the "grainy" appearance.  You may try Xanthan Gum at 0.1% if you still have the same grainy effect at the end of the emulsion.  you may try Sodium Hyaluronate at 0.1% which can give a significantly smoother result.  It is recommended to make a slurry of either Xanthan Gum or Sodium Hyaluronate with Glycerin, then, add it to the water phase with moderate mixing till complete hydration.  You should make sure that you attained the complete hydration step and no more fisheyes.  If it still has fisheyes you don't notice, it may turn into small grains by the end of the emulsion or luckily the heat may dissolve these small fisheyes as long as you are using Natural Thickeners.  The case is different if you are using Synthetic thickener like carbopol (Acrylates/C10-30 Alkyl Acrylate Crosspolymer), you may not be able to get ride of these fisheyes by the end of the emulsion

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