title: Anhydrous Carbopol polymer gels for the topical delivery of oxygen/water sensitive compounds.
abstract: OBJECTIVE
  The purpose of this study was the development and evaluation of an anhydrous glycerin-based Carbopol gel in order to study the stability of the oxygen/water-sensitive agent epigallocatechin gallate (EGCG).
  
  
  METHODS
  Various Carbopol polymers were investigated rheologically at concentrations of 0.25-1% using a Brookfield viscometer in order to evaluate their ability to form anhydrous glycerin-based formulations. The addition of Transcutol P was evaluated in order to create a gel that can be utilized for the incorporation of more lipophilic compounds. The suitability of standard neutralizers and their useful concentrations were determined to develop guidelines for formulation optimization. An accelerated stability study was performed at 50 degrees C to evaluate the degradation of EGCG in an anhydrous glycerin gel.
  
  
  RESULTS
  It was found that Carbopol 974 is the most efficient thickener for anhydrous glycerin formulations. In contrast to aqueous gels, anhydrous gels are formed without the addition of neutralizers. The rank-order viscosity of the nonneutralized gels studied was 974 > 971 > 981 > Pemulen TR-2 approximately 980. The addition of neutralizers resulted in a further increase in gel viscosity, with a maximum being reached at a concentration of approximately 0.5% w/w. The incorporation of Transcutol P resulted in a concentration-dependent loss of gel viscosity. The stability data showed that no degradation of EGCG had occurred.
  
  
  CONCLUSIONS
  It was shown that anhydrous glycerin-based Carbopol gels can be prepared without the need for neutralization. Such vehicles are promising for the incorporation of oxygen/water-sensitive drugs.
authors.affiliation: Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, Tucson, AZ 85721, USA. stefanp@cimalabs.com
authors.forename: Stefan
authors.initials: S
authors.lastname: Proniuk
authors.forename: James
authors.initials: J
authors.lastname: Blanchard
mesh_terms: D000180:Acrylic Resins; D002392:Catechin / Q000008:administration & dosage* / Q000031:analogs & derivatives* / Q000737:chemistry; D002626:Chemistry, Pharmaceutical; D016503:Drug Delivery Systems; D004355:Drug Stability; D005782:Gels; D005990:Glycerol / Q000008:administration & dosage; D010100:Oxygen; D011145:Polyvinyls / Q000008:administration & dosage*; D014783:Viscosity; D014867:Water
chemical_list: D000180:Acrylic Resins; D005782:Gels; D011145:Polyvinyls; D014867:Water; C006912:carboxypolymethylene; D002392:Catechin; C045651:epigallocatechin gallate; D005990:Glycerol; D010100:Oxygen